[v10,1/3] ipmi: ssif_bmc: Add SSIF BMC driver

The SMBus system interface (SSIF) IPMI BMC driver can be used to perform
in-band IPMI communication with their host in management (BMC) side.

Thanks Dan for the copy_from_user() fix in the link below.

Link: https://lore.kernel.org/linux-arm-kernel/20220310114119.13736-4-quan@os.amperecomputing.com/
Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
---
v10:
  + None

v9:
  + Fix dependence with I2C subsystem                            [Randy]
  + Remove useless error handling path                              [CJ]
  + Update comment for SSIF_ABORTING state                          [CJ]
  + Fix "unknown type name --u8"                     [kernel test robot]
  + Fix ssif_bmc_remove() to return void to align with recent kernel
    change                                                        [Quan]

v8:
  + Dropped ssif_bmc.h file and move its content to ssif_bmc.c   [Corey]
  + Add struct ipmi_ssif_msg to include/uapi/linux/ipmi_ssif_bmc.h
  header file                                                    [Corey]
  + Use unsigned int for len field in struct ipmi_ssif_msg       [Corey]
  + Avoid using packed structure                                 [Corey]
  + Add comment to clarify the logic flow                        [Corey]
  + Fix multipart read end with len=0 issue                      [Corey]
  + Refactor code handle the too big request message             [Corey]
  + Fix code indentation issue                                   [Corey]
  + Clean buffer before receiving request to avoid garbage        [Quan]
  + Fix the license to SPDX-License-Identifier: GPL-2.0-only      [Quan]

v7:
  + Remove unneccessary del_timer() in response_timeout()        [Corey]
  + Change compatible string from "ampere,ssif-bmc" to "ssif-bmc"  [Jae]
  + Add MODULE_DEVICE_TABLE(of, ssif_bmc_match), fix blank line    [Jae]
  + Dropped the use of ssif_msg_len() macro, use the len directly [Quan]
  + Solve possible issue if both response timer and ssif_bmc_write()
  occurred at the same time                                      [Corey]
  + Fix wrong return type of ssif_bmc_poll()         [kernel robot test]
  + Refactor and introduce ssif_part_buffer struct to replace the
  response_buf to manage each send/receive part of ssif           [Quan]
  + Change SSIF_BAD_SMBUS state to SSIF_ABORTING state           [Corey]
  + Support abort feature to skip the current bad request/response and
  wait until next new request                                    [Corey]
  + Refactor the PEC calculation to avoid the re-calculate the PEC on
  each I2C_SLAVE_WRITE_RECEIVED event                             [Quan]
  + Fix the use of error-proned idx                              [Corey]
  + Defer the test for valid SMBus command until the read/write part
  is determined                                                   [Quan]
  + Change/split unsupported_smbus_cmd() to
  supported_[write|read]_cmd()                                   [Corey]
  + Abort the request if somehow its size exceeded 255 bytes      [Quan]

v6:
  + Drop the use of slave_enable()                             [Wolfram]
  + Make i2c-aspeed to issue RxCmdLast command on all
  I2C_SLAVE_WRITE_REQUESTED event to assert NAK when slave busy   [Quan]
  + Make i2c slave to return -EBUSY when it's busy                [Quan]
  + Drop the aborting feature as return Completion Code 0xFF may stop
  host to retry and make ipmi_ssif.so fails to load               [Quan]
  + Add timer to recover slave from busy state when no response   [Quan]
  + Clean request/response buffer appropriately                   [Quan]
  + Add some minor change on error and warning messages           [Quan]

v5:
  + None

v4:
  + Send response with Completion code 0xFF when aborting         [Quan]
  + Added bounding check on SMBus writes and the whole request     [Dan]
  + Moved buffer to end of struct ssif_bmc_ctx to avoid context
    corruption if somehow buffer is written past the end           [Dan]
  + Return -EINVAL if userspace buffer too small, dont
    silence truncate                                       [Corey, Joel]
  + Not necessary to check NONBLOCK in lock                      [Corey]
  + Enforce one user at a time                                    [Joel]
  + Reject write with invalid response length from userspace     [Corey]
  + Add state machines for better ssif bmc state handling         [Quan]
  + Drop ssif_bmc_aspeed.c and make ssif_bmc.c is generic
    SSIF BMC driver                                               [Quan]
  + Change compatible string "aspeed,ast2500-ssif-bmc" to
    "ampere,ssif-bmc"                                             [Quan]
  + Abort current request with invalid SMBus write or
    invalid command                                               [Quan]
  + Abort all request if there is pending response                [Quan]
  + Changed validate_pec() to validate_request()                  [Quan]
  + Add unsupported_smbus_cmd() to handle unknown SMBus command   [Quan]
  + Print internal state string for ease investigating issue      [Quan]
  + Move to READY state on SLAVE_STOP event                       [Quan]
  + Change initilize_transfer() to process_smbus_cmd()            [Quan]
  + Introduce functions for each slave event                      [Quan]

v3:
  + Removed redundant license info                                [Joel]
  + Switched to use traditional if-else                           [Joel]
  + Removed unused ssif_bmc_ioctl()                               [Joel]
  + Made handle_request()/complete_response() to return void      [Joel]
  + Refactored send_ssif_bmc_response() and
  receive_ssif_bmc_request()                                     [Corey]
  + Removed mutex                                                [Corey]
  + Use spin_lock/unlock_irqsave/restore in callback             [Corey]
  + Removed the unnecessary memset                               [Corey]
  + Switch to use dev_err()                                      [Corey]

v2:
  + Fixed compiling error with COMPILE_TEST for arc
---
 drivers/char/ipmi/Kconfig          |  10 +
 drivers/char/ipmi/Makefile         |   1 +
 drivers/char/ipmi/ssif_bmc.c       | 873 +++++++++++++++++++++++++++++
 include/uapi/linux/ipmi_ssif_bmc.h |  18 +
 4 files changed, 902 insertions(+)
 create mode 100644 drivers/char/ipmi/ssif_bmc.c
 create mode 100644 include/uapi/linux/ipmi_ssif_bmc.h

On 04/10/2022 10:31, Quan Nguyen wrote:
> The SMBus system interface (SSIF) IPMI BMC driver can be used to perform
> in-band IPMI communication with their host in management (BMC) side.
>
> Thanks Dan for the copy_from_user() fix in the link below.
>
> Link: https://lore.kernel.org/linux-arm-kernel/20220310114119.13736-4-quan@os.amperecomputing.com/
> Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>

I have been testing this on our hardware and I don't seem to be able to 
get this driver working. I was using an older version.

I have hacked ssifbridged to deal with the change in len from u8 to 
unsigned int.

It works as long as I only ever send SSIF commands, any attempt to read 
a response crashes the state machine and the driver never recovers. No 
further SSIF comms is possible! (slave doesnt even ACK writes).

A couple of comments below on possible state machine errors.

Its possible I am doing something wrong!

> ---
> v10:
>    + None
>
> v9:
>    + Fix dependence with I2C subsystem                            [Randy]
>    + Remove useless error handling path                              [CJ]
>    + Update comment for SSIF_ABORTING state                          [CJ]
>    + Fix "unknown type name --u8"                     [kernel test robot]
>    + Fix ssif_bmc_remove() to return void to align with recent kernel
>      change                                                        [Quan]
>
> v8:
>    + Dropped ssif_bmc.h file and move its content to ssif_bmc.c   [Corey]
>    + Add struct ipmi_ssif_msg to include/uapi/linux/ipmi_ssif_bmc.h
>    header file                                                    [Corey]
>    + Use unsigned int for len field in struct ipmi_ssif_msg       [Corey]
>    + Avoid using packed structure                                 [Corey]
>    + Add comment to clarify the logic flow                        [Corey]
>    + Fix multipart read end with len=0 issue                      [Corey]
>    + Refactor code handle the too big request message             [Corey]
>    + Fix code indentation issue                                   [Corey]
>    + Clean buffer before receiving request to avoid garbage        [Quan]
>    + Fix the license to SPDX-License-Identifier: GPL-2.0-only      [Quan]
>
> v7:
>    + Remove unneccessary del_timer() in response_timeout()        [Corey]
>    + Change compatible string from "ampere,ssif-bmc" to "ssif-bmc"  [Jae]
>    + Add MODULE_DEVICE_TABLE(of, ssif_bmc_match), fix blank line    [Jae]
>    + Dropped the use of ssif_msg_len() macro, use the len directly [Quan]
>    + Solve possible issue if both response timer and ssif_bmc_write()
>    occurred at the same time                                      [Corey]
>    + Fix wrong return type of ssif_bmc_poll()         [kernel robot test]
>    + Refactor and introduce ssif_part_buffer struct to replace the
>    response_buf to manage each send/receive part of ssif           [Quan]
>    + Change SSIF_BAD_SMBUS state to SSIF_ABORTING state           [Corey]
>    + Support abort feature to skip the current bad request/response and
>    wait until next new request                                    [Corey]
>    + Refactor the PEC calculation to avoid the re-calculate the PEC on
>    each I2C_SLAVE_WRITE_RECEIVED event                             [Quan]
>    + Fix the use of error-proned idx                              [Corey]
>    + Defer the test for valid SMBus command until the read/write part
>    is determined                                                   [Quan]
>    + Change/split unsupported_smbus_cmd() to
>    supported_[write|read]_cmd()                                   [Corey]
>    + Abort the request if somehow its size exceeded 255 bytes      [Quan]
>
> v6:
>    + Drop the use of slave_enable()                             [Wolfram]
>    + Make i2c-aspeed to issue RxCmdLast command on all
>    I2C_SLAVE_WRITE_REQUESTED event to assert NAK when slave busy   [Quan]
>    + Make i2c slave to return -EBUSY when it's busy                [Quan]
>    + Drop the aborting feature as return Completion Code 0xFF may stop
>    host to retry and make ipmi_ssif.so fails to load               [Quan]
>    + Add timer to recover slave from busy state when no response   [Quan]
>    + Clean request/response buffer appropriately                   [Quan]
>    + Add some minor change on error and warning messages           [Quan]
>
> v5:
>    + None
>
> v4:
>    + Send response with Completion code 0xFF when aborting         [Quan]
>    + Added bounding check on SMBus writes and the whole request     [Dan]
>    + Moved buffer to end of struct ssif_bmc_ctx to avoid context
>      corruption if somehow buffer is written past the end           [Dan]
>    + Return -EINVAL if userspace buffer too small, dont
>      silence truncate                                       [Corey, Joel]
>    + Not necessary to check NONBLOCK in lock                      [Corey]
>    + Enforce one user at a time                                    [Joel]
>    + Reject write with invalid response length from userspace     [Corey]
>    + Add state machines for better ssif bmc state handling         [Quan]
>    + Drop ssif_bmc_aspeed.c and make ssif_bmc.c is generic
>      SSIF BMC driver                                               [Quan]
>    + Change compatible string "aspeed,ast2500-ssif-bmc" to
>      "ampere,ssif-bmc"                                             [Quan]
>    + Abort current request with invalid SMBus write or
>      invalid command                                               [Quan]
>    + Abort all request if there is pending response                [Quan]
>    + Changed validate_pec() to validate_request()                  [Quan]
>    + Add unsupported_smbus_cmd() to handle unknown SMBus command   [Quan]
>    + Print internal state string for ease investigating issue      [Quan]
>    + Move to READY state on SLAVE_STOP event                       [Quan]
>    + Change initilize_transfer() to process_smbus_cmd()            [Quan]
>    + Introduce functions for each slave event                      [Quan]
>
> v3:
>    + Removed redundant license info                                [Joel]
>    + Switched to use traditional if-else                           [Joel]
>    + Removed unused ssif_bmc_ioctl()                               [Joel]
>    + Made handle_request()/complete_response() to return void      [Joel]
>    + Refactored send_ssif_bmc_response() and
>    receive_ssif_bmc_request()                                     [Corey]
>    + Removed mutex                                                [Corey]
>    + Use spin_lock/unlock_irqsave/restore in callback             [Corey]
>    + Removed the unnecessary memset                               [Corey]
>    + Switch to use dev_err()                                      [Corey]
>
> v2:
>    + Fixed compiling error with COMPILE_TEST for arc
> ---
>   drivers/char/ipmi/Kconfig          |  10 +
>   drivers/char/ipmi/Makefile         |   1 +
>   drivers/char/ipmi/ssif_bmc.c       | 873 +++++++++++++++++++++++++++++
>   include/uapi/linux/ipmi_ssif_bmc.h |  18 +
>   4 files changed, 902 insertions(+)
>   create mode 100644 drivers/char/ipmi/ssif_bmc.c
>   create mode 100644 include/uapi/linux/ipmi_ssif_bmc.h
>
> diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig
> index 39565cf74b2c..b6c0d35fc1a5 100644
> --- a/drivers/char/ipmi/Kconfig
> +++ b/drivers/char/ipmi/Kconfig
> @@ -169,6 +169,16 @@ config ASPEED_BT_IPMI_BMC
>   	  found on Aspeed SOCs (AST2400 and AST2500). The driver
>   	  implements the BMC side of the BT interface.
>   
> +config SSIF_IPMI_BMC
> +	tristate "SSIF IPMI BMC driver"
> +	depends on I2C && I2C_SLAVE
> +	help
> +	  This enables the IPMI SMBus system interface (SSIF) at the
> +	  management (BMC) side.
> +
> +	  The driver implements the BMC side of the SMBus system
> +	  interface (SSIF).
> +
>   config IPMB_DEVICE_INTERFACE
>   	tristate 'IPMB Interface handler'
>   	depends on I2C
> diff --git a/drivers/char/ipmi/Makefile b/drivers/char/ipmi/Makefile
> index 7ce790efad92..cb6138b8ded9 100644
> --- a/drivers/char/ipmi/Makefile
> +++ b/drivers/char/ipmi/Makefile
> @@ -30,3 +30,4 @@ obj-$(CONFIG_ASPEED_BT_IPMI_BMC) += bt-bmc.o
>   obj-$(CONFIG_ASPEED_KCS_IPMI_BMC) += kcs_bmc_aspeed.o
>   obj-$(CONFIG_NPCM7XX_KCS_IPMI_BMC) += kcs_bmc_npcm7xx.o
>   obj-$(CONFIG_IPMB_DEVICE_INTERFACE) += ipmb_dev_int.o
> +obj-$(CONFIG_SSIF_IPMI_BMC) += ssif_bmc.o
> diff --git a/drivers/char/ipmi/ssif_bmc.c b/drivers/char/ipmi/ssif_bmc.c
> new file mode 100644
> index 000000000000..a7bb4b99000e
> --- /dev/null
> +++ b/drivers/char/ipmi/ssif_bmc.c
> @@ -0,0 +1,873 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * The driver for BMC side of SSIF interface
> + *
> + * Copyright (c) 2022, Ampere Computing LLC
> + *
> + */
> +
> +#include <linux/i2c.h>
> +#include <linux/miscdevice.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/poll.h>
> +#include <linux/sched.h>
> +#include <linux/mutex.h>
> +#include <linux/spinlock.h>
> +#include <linux/timer.h>
> +#include <linux/jiffies.h>
> +#include <linux/ipmi_ssif_bmc.h>
> +
> +#define DEVICE_NAME                             "ipmi-ssif-host"
> +
> +#define GET_8BIT_ADDR(addr_7bit)                (((addr_7bit) << 1) & 0xff)
> +
> +/* A standard SMBus Transaction is limited to 32 data bytes */
> +#define MAX_PAYLOAD_PER_TRANSACTION             32
> +/* Transaction includes the address, the command, the length and the PEC byte */
> +#define MAX_TRANSACTION                         (MAX_PAYLOAD_PER_TRANSACTION + 4)
> +
> +#define MAX_IPMI_DATA_PER_START_TRANSACTION     30
> +#define MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION    31
> +
> +#define SSIF_IPMI_SINGLEPART_WRITE              0x2
> +#define SSIF_IPMI_SINGLEPART_READ               0x3
> +#define SSIF_IPMI_MULTIPART_WRITE_START         0x6
> +#define SSIF_IPMI_MULTIPART_WRITE_MIDDLE        0x7
> +#define SSIF_IPMI_MULTIPART_WRITE_END           0x8
> +#define SSIF_IPMI_MULTIPART_READ_START          0x3
> +#define SSIF_IPMI_MULTIPART_READ_MIDDLE         0x9
> +
> +/*
> + * IPMI 2.0 Spec, section 12.7 SSIF Timing,
> + * Request-to-Response Time is T6max(250ms) - T1max(20ms) - 3ms = 227ms
> + * Recover ssif_bmc from busy state if it takes up to 500ms
> + */
> +#define RESPONSE_TIMEOUT                        500 /* ms */
> +
> +struct ssif_part_buffer {
> +	u8 address;
> +	u8 smbus_cmd;
> +	u8 length;
> +	u8 payload[MAX_PAYLOAD_PER_TRANSACTION];
> +	u8 pec;
> +	u8 index;
> +};
> +
> +/*
> + * SSIF internal states:
> + *   SSIF_READY         0x00 : Ready state
> + *   SSIF_START         0x01 : Start smbus transaction
> + *   SSIF_SMBUS_CMD     0x02 : Received SMBus command
> + *   SSIF_REQ_RECVING   0x03 : Receiving request
> + *   SSIF_RES_SENDING   0x04 : Sending response
> + *   SSIF_ABORTING      0x05 : Aborting state
> + */
> +enum ssif_state {
> +	SSIF_READY,
> +	SSIF_START,
> +	SSIF_SMBUS_CMD,
> +	SSIF_REQ_RECVING,
> +	SSIF_RES_SENDING,
> +	SSIF_ABORTING,
> +	SSIF_STATE_MAX
> +};
> +
> +struct ssif_bmc_ctx {
> +	struct i2c_client       *client;
> +	struct miscdevice       miscdev;
> +	int                     msg_idx;
> +	bool                    pec_support;
> +	/* ssif bmc spinlock */
> +	spinlock_t              lock;
> +	wait_queue_head_t       wait_queue;
> +	u8                      running;
> +	enum ssif_state         state;
> +	/* Timeout waiting for response */
> +	struct timer_list       response_timer;
> +	bool                    response_timer_inited;
> +	/* Flag to identify a Multi-part Read Transaction */
> +	bool                    is_singlepart_read;
> +	u8                      nbytes_processed;
> +	u8                      remain_len;
> +	u8                      recv_len;
> +	/* Block Number of a Multi-part Read Transaction */
> +	u8                      block_num;
> +	bool                    request_available;
> +	bool                    response_in_progress;
> +	bool                    busy;
> +	bool                    aborting;
> +	/* Buffer for SSIF Transaction part*/
> +	struct ssif_part_buffer part_buf;
> +	struct ipmi_ssif_msg    response;
> +	struct ipmi_ssif_msg    request;
> +};
> +
> +static inline struct ssif_bmc_ctx *to_ssif_bmc(struct file *file)
> +{
> +	return container_of(file->private_data, struct ssif_bmc_ctx, miscdev);
> +}
> +
> +static const char *state_to_string(enum ssif_state state)
> +{
> +	switch (state) {
> +	case SSIF_READY:
> +		return "SSIF_READY";
> +	case SSIF_START:
> +		return "SSIF_START";
> +	case SSIF_SMBUS_CMD:
> +		return "SSIF_SMBUS_CMD";
> +	case SSIF_REQ_RECVING:
> +		return "SSIF_REQ_RECVING";
> +	case SSIF_RES_SENDING:
> +		return "SSIF_RES_SENDING";
> +	case SSIF_ABORTING:
> +		return "SSIF_ABORTING";
> +	default:
> +		return "SSIF_STATE_UNKNOWN";
> +	}
> +}
> +
> +/* Handle SSIF message that will be sent to user */
> +static ssize_t ssif_bmc_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
> +	struct ipmi_ssif_msg msg;
> +	unsigned long flags;
> +	ssize_t ret;
> +
> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
> +	while (!ssif_bmc->request_available) {
> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +		if (file->f_flags & O_NONBLOCK)
> +			return -EAGAIN;
> +		ret = wait_event_interruptible(ssif_bmc->wait_queue,
> +					       ssif_bmc->request_available);
> +		if (ret)
> +			return ret;
> +		spin_lock_irqsave(&ssif_bmc->lock, flags);
> +	}
> +
> +	if (count < min_t(ssize_t,
> +			  sizeof_field(struct ipmi_ssif_msg, len) + ssif_bmc->request.len,
> +			  sizeof(struct ipmi_ssif_msg))) {
> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +		ret = -EINVAL;
> +	} else {
> +		count = min_t(ssize_t,
> +			      sizeof_field(struct ipmi_ssif_msg, len) + ssif_bmc->request.len,
> +			      sizeof(struct ipmi_ssif_msg));
> +		memcpy(&msg, &ssif_bmc->request, count);
> +		ssif_bmc->request_available = false;
> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +
> +		ret = copy_to_user(buf, &msg, count);
> +	}
> +
> +	return (ret < 0) ? ret : count;
> +}
> +
> +/* Handle SSIF message that is written by user */
> +static ssize_t ssif_bmc_write(struct file *file, const char __user *buf, size_t count,
> +			      loff_t *ppos)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
> +	struct ipmi_ssif_msg msg;
> +	unsigned long flags;
> +	ssize_t ret;
> +
> +	if (count > sizeof(struct ipmi_ssif_msg))
> +		return -EINVAL;
> +
> +	if (copy_from_user(&msg, buf, count))
> +		return -EFAULT;
> +
> +	if (!msg.len || count < sizeof_field(struct ipmi_ssif_msg, len) + msg.len)
> +		return -EINVAL;
> +
> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
> +	while (ssif_bmc->response_in_progress) {
> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +		if (file->f_flags & O_NONBLOCK)
> +			return -EAGAIN;
> +		ret = wait_event_interruptible(ssif_bmc->wait_queue,
> +					       !ssif_bmc->response_in_progress);
> +		if (ret)
> +			return ret;
> +		spin_lock_irqsave(&ssif_bmc->lock, flags);
> +	}
> +
> +	/*
> +	 * The write must complete before the response timeout fired, otherwise
> +	 * the response is aborted and wait for next request
> +	 * Return -EINVAL if the response is aborted
> +	 */
> +	ret = (ssif_bmc->response_timer_inited) ? 0 : -EINVAL;
> +	if (ret)
> +		goto exit;
> +
> +	del_timer(&ssif_bmc->response_timer);
> +	ssif_bmc->response_timer_inited = false;
> +
> +	memcpy(&ssif_bmc->response, &msg, count);
> +	ssif_bmc->is_singlepart_read = (msg.len <= MAX_PAYLOAD_PER_TRANSACTION);
> +
> +	ssif_bmc->response_in_progress = true;
> +
> +	/* ssif_bmc not busy */
> +	ssif_bmc->busy = false;
> +
> +	/* Clean old request buffer */
> +	memset(&ssif_bmc->request, 0, sizeof(struct ipmi_ssif_msg));
> +exit:
> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +
> +	return (ret < 0) ? ret : count;
> +}
> +
> +static int ssif_bmc_open(struct inode *inode, struct file *file)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
> +	int ret = 0;
> +
> +	spin_lock_irq(&ssif_bmc->lock);
> +	if (!ssif_bmc->running)
> +		ssif_bmc->running = 1;
> +	else
> +		ret = -EBUSY;
> +	spin_unlock_irq(&ssif_bmc->lock);
> +
> +	return ret;
> +}
> +
> +static __poll_t ssif_bmc_poll(struct file *file, poll_table *wait)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
> +	__poll_t mask = 0;
> +
> +	poll_wait(file, &ssif_bmc->wait_queue, wait);
> +
> +	spin_lock_irq(&ssif_bmc->lock);
> +	/* The request is available, userspace application can get the request */
> +	if (ssif_bmc->request_available)
> +		mask |= POLLIN;
> +
> +	spin_unlock_irq(&ssif_bmc->lock);
> +
> +	return mask;
> +}
> +
> +static int ssif_bmc_release(struct inode *inode, struct file *file)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
> +
> +	spin_lock_irq(&ssif_bmc->lock);
> +	ssif_bmc->running = 0;
> +	spin_unlock_irq(&ssif_bmc->lock);
> +
> +	return 0;
> +}
> +
> +/*
> + * System calls to device interface for user apps
> + */
> +static const struct file_operations ssif_bmc_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= ssif_bmc_open,
> +	.read		= ssif_bmc_read,
> +	.write		= ssif_bmc_write,
> +	.release	= ssif_bmc_release,
> +	.poll		= ssif_bmc_poll,
> +};
> +
> +/* Called with ssif_bmc->lock held. */
> +static void complete_response(struct ssif_bmc_ctx *ssif_bmc)
> +{
> +	/* Invalidate response in buffer to denote it having been sent. */
> +	ssif_bmc->response.len = 0;
> +	ssif_bmc->response_in_progress = false;
> +	ssif_bmc->nbytes_processed = 0;
> +	ssif_bmc->remain_len = 0;
> +	ssif_bmc->busy = false;
> +	memset(&ssif_bmc->part_buf, 0, sizeof(struct ssif_part_buffer));
> +	wake_up_all(&ssif_bmc->wait_queue);
> +}
> +
> +static void response_timeout(struct timer_list *t)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = from_timer(ssif_bmc, t, response_timer);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
> +
> +	/* Do nothing if the response is in progress */
> +	if (!ssif_bmc->response_in_progress) {
> +		/* Recover ssif_bmc from busy */
> +		ssif_bmc->busy = false;
> +		ssif_bmc->response_timer_inited = false;
> +		/* Set aborting flag */
> +		ssif_bmc->aborting = true;
> +	}
> +
> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +}
> +
> +/* Called with ssif_bmc->lock held. */
> +static void handle_request(struct ssif_bmc_ctx *ssif_bmc)
> +{
> +	/* set ssif_bmc to busy waiting for response */
> +	ssif_bmc->busy = true;
> +	/* Request message is available to process */
> +	ssif_bmc->request_available = true;
> +	/* Clean old response buffer */
> +	memset(&ssif_bmc->response, 0, sizeof(struct ipmi_ssif_msg));
> +	/* This is the new READ request.*/
> +	wake_up_all(&ssif_bmc->wait_queue);
> +
> +	/* Armed timer to recover slave from busy state in case of no response */
> +	if (!ssif_bmc->response_timer_inited) {
> +		timer_setup(&ssif_bmc->response_timer, response_timeout, 0);
> +		ssif_bmc->response_timer_inited = true;
> +	}
> +	mod_timer(&ssif_bmc->response_timer, jiffies + msecs_to_jiffies(RESPONSE_TIMEOUT));
> +}
> +
> +static void calculate_response_part_pec(struct ssif_part_buffer *part)
> +{
> +	u8 addr = part->address;
> +
> +	/* PEC - Start Read Address */
> +	part->pec = i2c_smbus_pec(0, &addr, 1);
> +	/* PEC - SSIF Command */
> +	part->pec = i2c_smbus_pec(part->pec, &part->smbus_cmd, 1);
> +	/* PEC - Restart Write Address */
> +	addr = addr | 0x01;
> +	part->pec = i2c_smbus_pec(part->pec, &addr, 1);
> +	part->pec = i2c_smbus_pec(part->pec, &part->length, 1);
> +	if (part->length)
> +		part->pec = i2c_smbus_pec(part->pec, part->payload, part->length);
> +}
> +
> +static void set_singlepart_response_buffer(struct ssif_bmc_ctx *ssif_bmc)
> +{
> +	struct ssif_part_buffer *part = &ssif_bmc->part_buf;
> +
> +	part->address = GET_8BIT_ADDR(ssif_bmc->client->addr);
> +	part->length = (u8)ssif_bmc->response.len;
> +
> +	/* Clear the rest to 0 */
> +	memset(part->payload + part->length, 0, MAX_PAYLOAD_PER_TRANSACTION - part->length);
> +	memcpy(&part->payload[0], &ssif_bmc->response.payload[0], part->length);
> +}
> +
> +static void set_multipart_response_buffer(struct ssif_bmc_ctx *ssif_bmc)
> +{
> +	struct ssif_part_buffer *part = &ssif_bmc->part_buf;
> +	u8 part_len = 0;
> +
> +	part->address = GET_8BIT_ADDR(ssif_bmc->client->addr);
> +	switch (part->smbus_cmd) {
> +	case SSIF_IPMI_MULTIPART_READ_START:
> +		/*
> +		 * Read Start length is 32 bytes.
> +		 * Read Start transfer first 30 bytes of IPMI response
> +		 * and 2 special code 0x00, 0x01.
> +		 */
> +		ssif_bmc->nbytes_processed = 0;
> +		ssif_bmc->block_num = 0;
> +		part->length = MAX_PAYLOAD_PER_TRANSACTION;
> +		part_len = MAX_IPMI_DATA_PER_START_TRANSACTION;
> +		ssif_bmc->remain_len = ssif_bmc->response.len - part_len;
> +
> +		part->payload[0] = 0x00; /* Start Flag */
> +		part->payload[1] = 0x01; /* Start Flag */
> +
> +		memcpy(&part->payload[2], &ssif_bmc->response.payload[0], part_len);
> +		break;
> +
> +	case SSIF_IPMI_MULTIPART_READ_MIDDLE:
> +		/*
> +		 * IPMI READ Middle or READ End messages can carry up to 31 bytes
> +		 * IPMI data plus block number byte.
> +		 */
> +		if (ssif_bmc->remain_len <= MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION) {
> +			/*
> +			 * This is READ End message
> +			 *  Return length is the remaining response data length
> +			 *  plus block number
> +			 *  Block number 0xFF is to indicate this is last message
> +			 *
> +			 */
> +			/* Clean the buffer */
> +			memset(&part->payload[0], 0, MAX_PAYLOAD_PER_TRANSACTION);
> +			part->length = ssif_bmc->remain_len + 1;
> +			part_len = ssif_bmc->remain_len;
> +			ssif_bmc->block_num = 0xFF;
> +			part->payload[0] = ssif_bmc->block_num;
> +		} else {
> +			/*
> +			 * This is READ Middle message
> +			 *  Response length is the maximum SMBUS transfer length
> +			 *  Block number byte is incremented
> +			 * Return length is maximum SMBUS transfer length
> +			 */
> +			part->length = MAX_PAYLOAD_PER_TRANSACTION;
> +			part_len = MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
> +			part->payload[0] = ssif_bmc->block_num;
> +			ssif_bmc->block_num++;
> +		}
> +
> +		ssif_bmc->remain_len -= part_len;
> +		memcpy(&part->payload[1], ssif_bmc->response.payload + ssif_bmc->nbytes_processed,
> +		       part_len);
> +		break;
> +
> +	default:
> +		/* Do not expect to go to this case */
> +		dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus command 0x%x\n",
> +			__func__, part->smbus_cmd);
> +		break;
> +	}
> +
> +	ssif_bmc->nbytes_processed += part_len;
> +}
> +
> +static bool supported_read_cmd(u8 cmd)
> +{
> +	if (cmd == SSIF_IPMI_SINGLEPART_READ ||
> +	    cmd == SSIF_IPMI_MULTIPART_READ_START ||
> +	    cmd == SSIF_IPMI_MULTIPART_READ_MIDDLE)
> +		return true;
> +
> +	return false;
> +}
> +
> +static bool supported_write_cmd(u8 cmd)
> +{
> +	if (cmd == SSIF_IPMI_SINGLEPART_WRITE ||
> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_START ||
> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_MIDDLE ||
> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_END)
> +		return true;
> +
> +	return false;
> +}
> +
> +/* Process the IPMI response that will be read by master */
> +static void handle_read_processed(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	struct ssif_part_buffer *part = &ssif_bmc->part_buf;
> +
> +	/* msg_idx start from 0 */
> +	if (part->index < part->length)
> +		*val = part->payload[part->index];
> +	else if (part->index == part->length && ssif_bmc->pec_support)
> +		*val = part->pec;
> +	else
> +		*val = 0;
> +
> +	part->index++;
> +}
> +
> +static void handle_write_received(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	/*
> +	 * The msg_idx must be 1 when first enter SSIF_REQ_RECVING state
> +	 * And it would never exceeded 36 bytes included the 32 bytes max payload +
> +	 * the address + the command + the len and the PEC.
> +	 */
> +	if (ssif_bmc->msg_idx < 1  || ssif_bmc->msg_idx > MAX_TRANSACTION)
> +		return;
> +
> +	if (ssif_bmc->msg_idx == 1) {
> +		ssif_bmc->part_buf.length = *val;
> +		ssif_bmc->part_buf.index = 0;
> +	} else {
> +		ssif_bmc->part_buf.payload[ssif_bmc->part_buf.index++] = *val;
> +	}
> +
> +	ssif_bmc->msg_idx++;
> +}
> +
> +static bool validate_request_part(struct ssif_bmc_ctx *ssif_bmc)
> +{
> +	struct ssif_part_buffer *part = &ssif_bmc->part_buf;
> +	bool ret = true;
> +	u8 cpec;
> +	u8 addr;
> +
> +	if (part->index == part->length) {
> +		/* PEC is not included */
> +		ssif_bmc->pec_support = false;
> +		ret = true;
> +		goto exit;
> +	}
> +
> +	if (part->index != part->length + 1) {
> +		ret = false;
> +		goto exit;
> +	}
> +
> +	/* PEC is included */
> +	ssif_bmc->pec_support = true;
> +	part->pec = part->payload[part->length];
> +	addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
> +	cpec = i2c_smbus_pec(0, &addr, 1);
> +	cpec = i2c_smbus_pec(cpec, &part->smbus_cmd, 1);
> +	cpec = i2c_smbus_pec(cpec, &part->length, 1);
> +	/*
> +	 * As SMBus specification does not allow the length
> +	 * (byte count) in the Write-Block protocol to be zero.
> +	 * Therefore, it is illegal to have the last Middle
> +	 * transaction in the sequence carry 32-byte and have
> +	 * a length of ‘0’ in the End transaction.
> +	 * But some users may try to use this way and we should
> +	 * prevent ssif_bmc driver broken in this case.
> +	 */
> +	if (part->length)
> +		cpec = i2c_smbus_pec(cpec, part->payload, part->length);
> +
> +	if (cpec != part->pec)
> +		ret = false;
> +
> +exit:
> +	return ret;
> +}
> +
> +static void process_request_part(struct ssif_bmc_ctx *ssif_bmc)
> +{
> +	struct ssif_part_buffer *part = &ssif_bmc->part_buf;
> +	unsigned int len;
> +
> +	switch (part->smbus_cmd) {
> +	case SSIF_IPMI_SINGLEPART_WRITE:
> +		/* save the whole part to request*/
> +		ssif_bmc->request.len = part->length;
> +		memcpy(ssif_bmc->request.payload, part->payload, part->length);
> +
> +		break;
> +	case SSIF_IPMI_MULTIPART_WRITE_START:
> +		ssif_bmc->request.len = 0;
> +
> +		fallthrough;
> +	case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
> +	case SSIF_IPMI_MULTIPART_WRITE_END:
> +		len = ssif_bmc->request.len + part->length;
> +		/* Do the bound check here, not allow the request len exceed 254 bytes */
> +		if (len > IPMI_SSIF_PAYLOAD_MAX) {
> +			dev_warn(&ssif_bmc->client->dev,
> +				 "Warn: Request exceeded 254 bytes, aborting");
> +			/* Request too long, aborting */
> +			ssif_bmc->aborting =  true;
> +		} else {
> +			memcpy(ssif_bmc->request.payload + ssif_bmc->request.len,
> +			       part->payload, part->length);
> +			ssif_bmc->request.len += part->length;
> +		}
> +		break;
> +	default:
> +		/* Do not expect to go to this case */
> +		dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus command 0x%x\n",
> +			__func__, part->smbus_cmd);
> +		break;
> +	}
> +}
> +
> +static void process_smbus_cmd(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	/* SMBUS command can vary (single or multi-part) */
> +	ssif_bmc->part_buf.smbus_cmd = *val;
> +	ssif_bmc->msg_idx = 1;
> +	memset(&ssif_bmc->part_buf.payload[0], 0, MAX_PAYLOAD_PER_TRANSACTION);
> +
> +	if (*val == SSIF_IPMI_SINGLEPART_WRITE || *val == SSIF_IPMI_MULTIPART_WRITE_START) {
> +		/*
> +		 * The response maybe not come in-time, causing host SSIF driver
> +		 * to timeout and resend a new request. In such case check for
> +		 * pending response and clear it
> +		 */
> +		if (ssif_bmc->response_in_progress)
> +			complete_response(ssif_bmc);
> +
> +		/* This is new request, flip aborting flag if set */
> +		if (ssif_bmc->aborting)
> +			ssif_bmc->aborting = false;
> +	}
> +}
> +
> +static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	if (ssif_bmc->state == SSIF_READY ||
Is this actually correct? The state machine seems to set this as the 
default state and in my testing we seem to always reach here with the 
state == SSIF_READY?
> +	    ssif_bmc->state == SSIF_START ||
> +	    ssif_bmc->state == SSIF_REQ_RECVING ||
> +	    ssif_bmc->state == SSIF_RES_SENDING) {
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s unexpected READ REQUESTED in state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));
> +		ssif_bmc->state = SSIF_ABORTING;
> +		*val = 0;
> +		return;
> +
> +	} else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
> +		if (!supported_read_cmd(ssif_bmc->part_buf.smbus_cmd)) {
> +			dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus read command=0x%x",
> +				 ssif_bmc->part_buf.smbus_cmd);
> +			ssif_bmc->aborting = true;
> +		}
> +
> +		if (ssif_bmc->aborting)
> +			ssif_bmc->state = SSIF_ABORTING;
> +		else
> +			ssif_bmc->state = SSIF_RES_SENDING;
> +	}
> +
> +	ssif_bmc->msg_idx = 0;
> +
> +	/* Send 0 if there is nothing to send */
> +	if (!ssif_bmc->response_in_progress || ssif_bmc->state == SSIF_ABORTING) {
> +		*val = 0;
> +		return;
> +	}
> +
> +	if (ssif_bmc->is_singlepart_read)
> +		set_singlepart_response_buffer(ssif_bmc);
> +	else
> +		set_multipart_response_buffer(ssif_bmc);
> +
> +	calculate_response_part_pec(&ssif_bmc->part_buf);
> +	ssif_bmc->part_buf.index = 0;
> +	*val = ssif_bmc->part_buf.length;
> +}
> +
> +static void on_read_processed_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	if (ssif_bmc->state == SSIF_READY ||
Same comment as above?
> +	    ssif_bmc->state == SSIF_START ||
> +	    ssif_bmc->state == SSIF_REQ_RECVING ||
> +	    ssif_bmc->state == SSIF_SMBUS_CMD) {
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s unexpected READ PROCESSED in state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));
> +		ssif_bmc->state = SSIF_ABORTING;
> +		*val = 0;
> +		return;
> +	}
> +
> +	/* Send 0 if there is nothing to send */
> +	if (!ssif_bmc->response_in_progress || ssif_bmc->state == SSIF_ABORTING) {
> +		*val = 0;
> +		return;
> +	}
> +
> +	handle_read_processed(ssif_bmc, val);
> +}
> +
> +static void on_write_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	if (ssif_bmc->state == SSIF_READY || ssif_bmc->state == SSIF_SMBUS_CMD) {
> +		ssif_bmc->state = SSIF_START;
> +
> +	} else if (ssif_bmc->state == SSIF_START ||
> +		   ssif_bmc->state == SSIF_REQ_RECVING ||
> +		   ssif_bmc->state == SSIF_RES_SENDING) {
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s unexpected WRITE REQUEST in state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));
> +		ssif_bmc->state = SSIF_ABORTING;
> +		return;
> +	}
> +
> +	ssif_bmc->msg_idx = 0;
> +	ssif_bmc->part_buf.address = *val;
> +}
> +
> +static void on_write_received_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	if (ssif_bmc->state == SSIF_READY ||
> +	    ssif_bmc->state == SSIF_RES_SENDING) {
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s unexpected WRITE RECEIVED in state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));
> +		ssif_bmc->state = SSIF_ABORTING;
> +
> +	} else if (ssif_bmc->state == SSIF_START) {
> +		ssif_bmc->state = SSIF_SMBUS_CMD;
> +
> +	} else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
> +		if (!supported_write_cmd(ssif_bmc->part_buf.smbus_cmd)) {
> +			dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus write command=0x%x",
> +				 ssif_bmc->part_buf.smbus_cmd);
> +			ssif_bmc->aborting = true;
> +		}
> +
> +		if (ssif_bmc->aborting)
> +			ssif_bmc->state = SSIF_ABORTING;
> +		else
> +			ssif_bmc->state = SSIF_REQ_RECVING;
> +	}
> +
> +	/* This is response sending state */
> +	if (ssif_bmc->state == SSIF_REQ_RECVING)
> +		handle_write_received(ssif_bmc, val);
> +	else if (ssif_bmc->state == SSIF_SMBUS_CMD)
> +		process_smbus_cmd(ssif_bmc, val);
> +}
> +
> +static void on_stop_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	if (ssif_bmc->state == SSIF_READY ||
> +	    ssif_bmc->state == SSIF_START ||
> +	    ssif_bmc->state == SSIF_SMBUS_CMD ||
> +	    ssif_bmc->state == SSIF_ABORTING) {
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s unexpected SLAVE STOP in state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));
> +		ssif_bmc->state = SSIF_READY;
> +
> +	} else if (ssif_bmc->state == SSIF_REQ_RECVING) {
> +		if (validate_request_part(ssif_bmc)) {
> +			process_request_part(ssif_bmc);
> +			if (ssif_bmc->part_buf.smbus_cmd == SSIF_IPMI_SINGLEPART_WRITE ||
> +			    ssif_bmc->part_buf.smbus_cmd == SSIF_IPMI_MULTIPART_WRITE_END)
> +				handle_request(ssif_bmc);
> +			ssif_bmc->state = SSIF_READY;
> +		} else {
> +			/*
> +			 * A BMC that receives an invalid request drop the data for the write
> +			 * transaction and any further transactions (read or write) until
> +			 * the next valid read or write Start transaction is received
> +			 */
> +			dev_err(&ssif_bmc->client->dev, "Error: invalid pec\n");
> +			ssif_bmc->aborting = true;
> +		}
> +	} else if (ssif_bmc->state == SSIF_RES_SENDING) {
> +		if (ssif_bmc->is_singlepart_read || ssif_bmc->block_num == 0xFF)
> +			/* Invalidate response buffer to denote it is sent */
> +			complete_response(ssif_bmc);
> +		ssif_bmc->state = SSIF_READY;
> +	}
> +
> +	/* Reset message index */
> +	ssif_bmc->msg_idx = 0;
> +}
> +
> +/*
> + * Callback function to handle I2C slave events
> + */
> +static int ssif_bmc_cb(struct i2c_client *client, enum i2c_slave_event event, u8 *val)
> +{
> +	unsigned long flags;
> +	struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
> +	int ret = 0;
> +
> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
> +
> +	switch (event) {
> +	case I2C_SLAVE_READ_REQUESTED:
> +		on_read_requested_event(ssif_bmc, val);
> +		break;
> +
> +	case I2C_SLAVE_WRITE_REQUESTED:
> +		on_write_requested_event(ssif_bmc, val);
> +		break;
> +
> +	case I2C_SLAVE_READ_PROCESSED:
> +		on_read_processed_event(ssif_bmc, val);
> +		break;
> +
> +	case I2C_SLAVE_WRITE_RECEIVED:
> +		on_write_received_event(ssif_bmc, val);
> +		break;
> +
> +	case I2C_SLAVE_STOP:
> +		on_stop_event(ssif_bmc, val);
> +		break;
> +
> +	default:
> +		dev_warn(&ssif_bmc->client->dev, "Warn: Unknown i2c slave event\n");
> +		break;
> +	}
> +
> +	if (!ssif_bmc->aborting && ssif_bmc->busy)
> +		ret = -EBUSY;
> +
> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +
> +	return ret;
> +}
> +
> +static int ssif_bmc_probe(struct i2c_client *client, const struct i2c_device_id *id)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc;
> +	int ret;
> +
> +	ssif_bmc = devm_kzalloc(&client->dev, sizeof(*ssif_bmc), GFP_KERNEL);
> +	if (!ssif_bmc)
> +		return -ENOMEM;
> +
> +	spin_lock_init(&ssif_bmc->lock);
> +
> +	init_waitqueue_head(&ssif_bmc->wait_queue);
> +	ssif_bmc->request_available = false;
> +	ssif_bmc->response_in_progress = false;
> +	ssif_bmc->busy = false;
> +	ssif_bmc->response_timer_inited = false;
> +
> +	/* Register misc device interface */
> +	ssif_bmc->miscdev.minor = MISC_DYNAMIC_MINOR;
> +	ssif_bmc->miscdev.name = DEVICE_NAME;
> +	ssif_bmc->miscdev.fops = &ssif_bmc_fops;
> +	ssif_bmc->miscdev.parent = &client->dev;
> +	ret = misc_register(&ssif_bmc->miscdev);
> +	if (ret)
> +		return ret;
> +
> +	ssif_bmc->client = client;
> +	ssif_bmc->client->flags |= I2C_CLIENT_SLAVE;
> +
> +	/* Register I2C slave */
> +	i2c_set_clientdata(client, ssif_bmc);
> +	ret = i2c_slave_register(client, ssif_bmc_cb);
> +	if (ret)
> +		misc_deregister(&ssif_bmc->miscdev);
> +
> +	return ret;
> +}
> +
> +static void ssif_bmc_remove(struct i2c_client *client)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
> +
> +	i2c_slave_unregister(client);
> +	misc_deregister(&ssif_bmc->miscdev);
> +}
> +
> +static const struct of_device_id ssif_bmc_match[] = {
> +	{ .compatible = "ssif-bmc" },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, ssif_bmc_match);
> +
> +static const struct i2c_device_id ssif_bmc_id[] = {
> +	{ DEVICE_NAME, 0 },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(i2c, ssif_bmc_id);
> +
> +static struct i2c_driver ssif_bmc_driver = {
> +	.driver         = {
> +		.name           = DEVICE_NAME,
> +		.of_match_table = ssif_bmc_match,
> +	},
> +	.probe          = ssif_bmc_probe,
> +	.remove         = ssif_bmc_remove,
> +	.id_table       = ssif_bmc_id,
> +};
> +
> +module_i2c_driver(ssif_bmc_driver);
> +
> +MODULE_AUTHOR("Quan Nguyen <quan@os.amperecomputing.com>");
> +MODULE_AUTHOR("Chuong Tran <chuong@os.amperecomputing.com>");
> +MODULE_DESCRIPTION("Linux device driver of the BMC IPMI SSIF interface.");
> +MODULE_LICENSE("GPL");
> diff --git a/include/uapi/linux/ipmi_ssif_bmc.h b/include/uapi/linux/ipmi_ssif_bmc.h
> new file mode 100644
> index 000000000000..1c6a753dad08
> --- /dev/null
> +++ b/include/uapi/linux/ipmi_ssif_bmc.h
> @@ -0,0 +1,18 @@
> +/* SPDX-License-Identifier: GPL-2.0-only WITH Linux-syscall-note*/
> +/*
> + * Copyright (c) 2022, Ampere Computing LLC.
> + */
> +
> +#ifndef _UAPI_LINUX_IPMI_SSIF_BMC_H
> +#define _UAPI_LINUX_IPMI_SSIF_BMC_H
> +
> +#include <linux/types.h>
> +
> +/* Max length of ipmi ssif message included netfn and cmd field */
> +#define IPMI_SSIF_PAYLOAD_MAX         254
> +struct ipmi_ssif_msg {
> +	unsigned int len;
> +	__u8    payload[IPMI_SSIF_PAYLOAD_MAX];
> +};
> +
> +#endif /* _UAPI_LINUX_IPMI_SSIF_BMC_H */

On 07/10/2022 20:26, Graeme Gregory wrote:
> 
> On 04/10/2022 10:31, Quan Nguyen wrote:
>> The SMBus system interface (SSIF) IPMI BMC driver can be used to perform
>> in-band IPMI communication with their host in management (BMC) side.
>>
>> Thanks Dan for the copy_from_user() fix in the link below.
>>
>> Link: 
>> https://lore.kernel.org/linux-arm-kernel/20220310114119.13736-4-quan@os.amperecomputing.com/
>> Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
> 
> I have been testing this on our hardware and I don't seem to be able to 
> get this driver working. I was using an older version.
> 
> I have hacked ssifbridged to deal with the change in len from u8 to 
> unsigned int.
> 
> It works as long as I only ever send SSIF commands, any attempt to read 
> a response crashes the state machine and the driver never recovers. No 
> further SSIF comms is possible! (slave doesnt even ACK writes).
> 
> A couple of comments below on possible state machine errors.
> 
> Its possible I am doing something wrong!
> 

Thanks Graeme for the test and the comments.

What's your testing hardware?

This was tested with Aspeed ast2500 and ast2600 with the patch series 
[1] below applied.

If you use the same hw, could you pick the series and see if any thing 
improve ?

[1] 
https://lore.kernel.org/all/20210616031046.2317-1-quan@os.amperecomputing.com/

>> ---
>> v10:
>>    + None
>>
>> v9:
>>    + Fix dependence with I2C subsystem                            [Randy]
>>    + Remove useless error handling path                              [CJ]
>>    + Update comment for SSIF_ABORTING state                          [CJ]
>>    + Fix "unknown type name --u8"                     [kernel test robot]
>>    + Fix ssif_bmc_remove() to return void to align with recent kernel
>>      change                                                        [Quan]
>>
>> v8:
>>    + Dropped ssif_bmc.h file and move its content to ssif_bmc.c   [Corey]
>>    + Add struct ipmi_ssif_msg to include/uapi/linux/ipmi_ssif_bmc.h
>>    header file                                                    [Corey]
>>    + Use unsigned int for len field in struct ipmi_ssif_msg       [Corey]
>>    + Avoid using packed structure                                 [Corey]
>>    + Add comment to clarify the logic flow                        [Corey]
>>    + Fix multipart read end with len=0 issue                      [Corey]
>>    + Refactor code handle the too big request message             [Corey]
>>    + Fix code indentation issue                                   [Corey]
>>    + Clean buffer before receiving request to avoid garbage        [Quan]
>>    + Fix the license to SPDX-License-Identifier: GPL-2.0-only      [Quan]
>>
>> v7:
>>    + Remove unneccessary del_timer() in response_timeout()        [Corey]
>>    + Change compatible string from "ampere,ssif-bmc" to "ssif-bmc"  [Jae]
>>    + Add MODULE_DEVICE_TABLE(of, ssif_bmc_match), fix blank line    [Jae]
>>    + Dropped the use of ssif_msg_len() macro, use the len directly [Quan]
>>    + Solve possible issue if both response timer and ssif_bmc_write()
>>    occurred at the same time                                      [Corey]
>>    + Fix wrong return type of ssif_bmc_poll()         [kernel robot test]
>>    + Refactor and introduce ssif_part_buffer struct to replace the
>>    response_buf to manage each send/receive part of ssif           [Quan]
>>    + Change SSIF_BAD_SMBUS state to SSIF_ABORTING state           [Corey]
>>    + Support abort feature to skip the current bad request/response and
>>    wait until next new request                                    [Corey]
>>    + Refactor the PEC calculation to avoid the re-calculate the PEC on
>>    each I2C_SLAVE_WRITE_RECEIVED event                             [Quan]
>>    + Fix the use of error-proned idx                              [Corey]
>>    + Defer the test for valid SMBus command until the read/write part
>>    is determined                                                   [Quan]
>>    + Change/split unsupported_smbus_cmd() to
>>    supported_[write|read]_cmd()                                   [Corey]
>>    + Abort the request if somehow its size exceeded 255 bytes      [Quan]
>>
>> v6:
>>    + Drop the use of slave_enable()                             [Wolfram]
>>    + Make i2c-aspeed to issue RxCmdLast command on all
>>    I2C_SLAVE_WRITE_REQUESTED event to assert NAK when slave busy   [Quan]
>>    + Make i2c slave to return -EBUSY when it's busy                [Quan]
>>    + Drop the aborting feature as return Completion Code 0xFF may stop
>>    host to retry and make ipmi_ssif.so fails to load               [Quan]
>>    + Add timer to recover slave from busy state when no response   [Quan]
>>    + Clean request/response buffer appropriately                   [Quan]
>>    + Add some minor change on error and warning messages           [Quan]
>>
>> v5:
>>    + None
>>
>> v4:
>>    + Send response with Completion code 0xFF when aborting         [Quan]
>>    + Added bounding check on SMBus writes and the whole request     [Dan]
>>    + Moved buffer to end of struct ssif_bmc_ctx to avoid context
>>      corruption if somehow buffer is written past the end           [Dan]
>>    + Return -EINVAL if userspace buffer too small, dont
>>      silence truncate                                       [Corey, Joel]
>>    + Not necessary to check NONBLOCK in lock                      [Corey]
>>    + Enforce one user at a time                                    [Joel]
>>    + Reject write with invalid response length from userspace     [Corey]
>>    + Add state machines for better ssif bmc state handling         [Quan]
>>    + Drop ssif_bmc_aspeed.c and make ssif_bmc.c is generic
>>      SSIF BMC driver                                               [Quan]
>>    + Change compatible string "aspeed,ast2500-ssif-bmc" to
>>      "ampere,ssif-bmc"                                             [Quan]
>>    + Abort current request with invalid SMBus write or
>>      invalid command                                               [Quan]
>>    + Abort all request if there is pending response                [Quan]
>>    + Changed validate_pec() to validate_request()                  [Quan]
>>    + Add unsupported_smbus_cmd() to handle unknown SMBus command   [Quan]
>>    + Print internal state string for ease investigating issue      [Quan]
>>    + Move to READY state on SLAVE_STOP event                       [Quan]
>>    + Change initilize_transfer() to process_smbus_cmd()            [Quan]
>>    + Introduce functions for each slave event                      [Quan]
>>
>> v3:
>>    + Removed redundant license info                                [Joel]
>>    + Switched to use traditional if-else                           [Joel]
>>    + Removed unused ssif_bmc_ioctl()                               [Joel]
>>    + Made handle_request()/complete_response() to return void      [Joel]
>>    + Refactored send_ssif_bmc_response() and
>>    receive_ssif_bmc_request()                                     [Corey]
>>    + Removed mutex                                                [Corey]
>>    + Use spin_lock/unlock_irqsave/restore in callback             [Corey]
>>    + Removed the unnecessary memset                               [Corey]
>>    + Switch to use dev_err()                                      [Corey]
>>
>> v2:
>>    + Fixed compiling error with COMPILE_TEST for arc
>> ---
>>   drivers/char/ipmi/Kconfig          |  10 +
>>   drivers/char/ipmi/Makefile         |   1 +
>>   drivers/char/ipmi/ssif_bmc.c       | 873 +++++++++++++++++++++++++++++
>>   include/uapi/linux/ipmi_ssif_bmc.h |  18 +
>>   4 files changed, 902 insertions(+)
>>   create mode 100644 drivers/char/ipmi/ssif_bmc.c
>>   create mode 100644 include/uapi/linux/ipmi_ssif_bmc.h
>>
>> diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig
>> index 39565cf74b2c..b6c0d35fc1a5 100644
>> --- a/drivers/char/ipmi/Kconfig
>> +++ b/drivers/char/ipmi/Kconfig
>> @@ -169,6 +169,16 @@ config ASPEED_BT_IPMI_BMC
>>         found on Aspeed SOCs (AST2400 and AST2500). The driver
>>         implements the BMC side of the BT interface.
>> +config SSIF_IPMI_BMC
>> +    tristate "SSIF IPMI BMC driver"
>> +    depends on I2C && I2C_SLAVE
>> +    help
>> +      This enables the IPMI SMBus system interface (SSIF) at the
>> +      management (BMC) side.
>> +
>> +      The driver implements the BMC side of the SMBus system
>> +      interface (SSIF).
>> +
>>   config IPMB_DEVICE_INTERFACE
>>       tristate 'IPMB Interface handler'
>>       depends on I2C
>> diff --git a/drivers/char/ipmi/Makefile b/drivers/char/ipmi/Makefile
>> index 7ce790efad92..cb6138b8ded9 100644
>> --- a/drivers/char/ipmi/Makefile
>> +++ b/drivers/char/ipmi/Makefile
>> @@ -30,3 +30,4 @@ obj-$(CONFIG_ASPEED_BT_IPMI_BMC) += bt-bmc.o
>>   obj-$(CONFIG_ASPEED_KCS_IPMI_BMC) += kcs_bmc_aspeed.o
>>   obj-$(CONFIG_NPCM7XX_KCS_IPMI_BMC) += kcs_bmc_npcm7xx.o
>>   obj-$(CONFIG_IPMB_DEVICE_INTERFACE) += ipmb_dev_int.o
>> +obj-$(CONFIG_SSIF_IPMI_BMC) += ssif_bmc.o
>> diff --git a/drivers/char/ipmi/ssif_bmc.c b/drivers/char/ipmi/ssif_bmc.c
>> new file mode 100644
>> index 000000000000..a7bb4b99000e
>> --- /dev/null
>> +++ b/drivers/char/ipmi/ssif_bmc.c
>> @@ -0,0 +1,873 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * The driver for BMC side of SSIF interface
>> + *
>> + * Copyright (c) 2022, Ampere Computing LLC
>> + *
>> + */
>> +
>> +#include <linux/i2c.h>
>> +#include <linux/miscdevice.h>
>> +#include <linux/module.h>
>> +#include <linux/of.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/poll.h>
>> +#include <linux/sched.h>
>> +#include <linux/mutex.h>
>> +#include <linux/spinlock.h>
>> +#include <linux/timer.h>
>> +#include <linux/jiffies.h>
>> +#include <linux/ipmi_ssif_bmc.h>
>> +
>> +#define DEVICE_NAME                             "ipmi-ssif-host"
>> +
>> +#define GET_8BIT_ADDR(addr_7bit)                (((addr_7bit) << 1) & 
>> 0xff)
>> +
>> +/* A standard SMBus Transaction is limited to 32 data bytes */
>> +#define MAX_PAYLOAD_PER_TRANSACTION             32
>> +/* Transaction includes the address, the command, the length and the 
>> PEC byte */
>> +#define MAX_TRANSACTION                         
>> (MAX_PAYLOAD_PER_TRANSACTION + 4)
>> +
>> +#define MAX_IPMI_DATA_PER_START_TRANSACTION     30
>> +#define MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION    31
>> +
>> +#define SSIF_IPMI_SINGLEPART_WRITE              0x2
>> +#define SSIF_IPMI_SINGLEPART_READ               0x3
>> +#define SSIF_IPMI_MULTIPART_WRITE_START         0x6
>> +#define SSIF_IPMI_MULTIPART_WRITE_MIDDLE        0x7
>> +#define SSIF_IPMI_MULTIPART_WRITE_END           0x8
>> +#define SSIF_IPMI_MULTIPART_READ_START          0x3
>> +#define SSIF_IPMI_MULTIPART_READ_MIDDLE         0x9
>> +
>> +/*
>> + * IPMI 2.0 Spec, section 12.7 SSIF Timing,
>> + * Request-to-Response Time is T6max(250ms) - T1max(20ms) - 3ms = 227ms
>> + * Recover ssif_bmc from busy state if it takes up to 500ms
>> + */
>> +#define RESPONSE_TIMEOUT                        500 /* ms */
>> +
>> +struct ssif_part_buffer {
>> +    u8 address;
>> +    u8 smbus_cmd;
>> +    u8 length;
>> +    u8 payload[MAX_PAYLOAD_PER_TRANSACTION];
>> +    u8 pec;
>> +    u8 index;
>> +};
>> +
>> +/*
>> + * SSIF internal states:
>> + *   SSIF_READY         0x00 : Ready state
>> + *   SSIF_START         0x01 : Start smbus transaction
>> + *   SSIF_SMBUS_CMD     0x02 : Received SMBus command
>> + *   SSIF_REQ_RECVING   0x03 : Receiving request
>> + *   SSIF_RES_SENDING   0x04 : Sending response
>> + *   SSIF_ABORTING      0x05 : Aborting state
>> + */
>> +enum ssif_state {
>> +    SSIF_READY,
>> +    SSIF_START,
>> +    SSIF_SMBUS_CMD,
>> +    SSIF_REQ_RECVING,
>> +    SSIF_RES_SENDING,
>> +    SSIF_ABORTING,
>> +    SSIF_STATE_MAX
>> +};
>> +
>> +struct ssif_bmc_ctx {
>> +    struct i2c_client       *client;
>> +    struct miscdevice       miscdev;
>> +    int                     msg_idx;
>> +    bool                    pec_support;
>> +    /* ssif bmc spinlock */
>> +    spinlock_t              lock;
>> +    wait_queue_head_t       wait_queue;
>> +    u8                      running;
>> +    enum ssif_state         state;
>> +    /* Timeout waiting for response */
>> +    struct timer_list       response_timer;
>> +    bool                    response_timer_inited;
>> +    /* Flag to identify a Multi-part Read Transaction */
>> +    bool                    is_singlepart_read;
>> +    u8                      nbytes_processed;
>> +    u8                      remain_len;
>> +    u8                      recv_len;
>> +    /* Block Number of a Multi-part Read Transaction */
>> +    u8                      block_num;
>> +    bool                    request_available;
>> +    bool                    response_in_progress;
>> +    bool                    busy;
>> +    bool                    aborting;
>> +    /* Buffer for SSIF Transaction part*/
>> +    struct ssif_part_buffer part_buf;
>> +    struct ipmi_ssif_msg    response;
>> +    struct ipmi_ssif_msg    request;
>> +};
>> +
>> +static inline struct ssif_bmc_ctx *to_ssif_bmc(struct file *file)
>> +{
>> +    return container_of(file->private_data, struct ssif_bmc_ctx, 
>> miscdev);
>> +}
>> +
>> +static const char *state_to_string(enum ssif_state state)
>> +{
>> +    switch (state) {
>> +    case SSIF_READY:
>> +        return "SSIF_READY";
>> +    case SSIF_START:
>> +        return "SSIF_START";
>> +    case SSIF_SMBUS_CMD:
>> +        return "SSIF_SMBUS_CMD";
>> +    case SSIF_REQ_RECVING:
>> +        return "SSIF_REQ_RECVING";
>> +    case SSIF_RES_SENDING:
>> +        return "SSIF_RES_SENDING";
>> +    case SSIF_ABORTING:
>> +        return "SSIF_ABORTING";
>> +    default:
>> +        return "SSIF_STATE_UNKNOWN";
>> +    }
>> +}
>> +
>> +/* Handle SSIF message that will be sent to user */
>> +static ssize_t ssif_bmc_read(struct file *file, char __user *buf, 
>> size_t count, loff_t *ppos)
>> +{
>> +    struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +    struct ipmi_ssif_msg msg;
>> +    unsigned long flags;
>> +    ssize_t ret;
>> +
>> +    spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +    while (!ssif_bmc->request_available) {
>> +        spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +        if (file->f_flags & O_NONBLOCK)
>> +            return -EAGAIN;
>> +        ret = wait_event_interruptible(ssif_bmc->wait_queue,
>> +                           ssif_bmc->request_available);
>> +        if (ret)
>> +            return ret;
>> +        spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +    }
>> +
>> +    if (count < min_t(ssize_t,
>> +              sizeof_field(struct ipmi_ssif_msg, len) + 
>> ssif_bmc->request.len,
>> +              sizeof(struct ipmi_ssif_msg))) {
>> +        spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +        ret = -EINVAL;
>> +    } else {
>> +        count = min_t(ssize_t,
>> +                  sizeof_field(struct ipmi_ssif_msg, len) + 
>> ssif_bmc->request.len,
>> +                  sizeof(struct ipmi_ssif_msg));
>> +        memcpy(&msg, &ssif_bmc->request, count);
>> +        ssif_bmc->request_available = false;
>> +        spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +
>> +        ret = copy_to_user(buf, &msg, count);
>> +    }
>> +
>> +    return (ret < 0) ? ret : count;
>> +}
>> +
>> +/* Handle SSIF message that is written by user */
>> +static ssize_t ssif_bmc_write(struct file *file, const char __user 
>> *buf, size_t count,
>> +                  loff_t *ppos)
>> +{
>> +    struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +    struct ipmi_ssif_msg msg;
>> +    unsigned long flags;
>> +    ssize_t ret;
>> +
>> +    if (count > sizeof(struct ipmi_ssif_msg))
>> +        return -EINVAL;
>> +
>> +    if (copy_from_user(&msg, buf, count))
>> +        return -EFAULT;
>> +
>> +    if (!msg.len || count < sizeof_field(struct ipmi_ssif_msg, len) + 
>> msg.len)
>> +        return -EINVAL;
>> +
>> +    spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +    while (ssif_bmc->response_in_progress) {
>> +        spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +        if (file->f_flags & O_NONBLOCK)
>> +            return -EAGAIN;
>> +        ret = wait_event_interruptible(ssif_bmc->wait_queue,
>> +                           !ssif_bmc->response_in_progress);
>> +        if (ret)
>> +            return ret;
>> +        spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +    }
>> +
>> +    /*
>> +     * The write must complete before the response timeout fired, 
>> otherwise
>> +     * the response is aborted and wait for next request
>> +     * Return -EINVAL if the response is aborted
>> +     */
>> +    ret = (ssif_bmc->response_timer_inited) ? 0 : -EINVAL;
>> +    if (ret)
>> +        goto exit;
>> +
>> +    del_timer(&ssif_bmc->response_timer);
>> +    ssif_bmc->response_timer_inited = false;
>> +
>> +    memcpy(&ssif_bmc->response, &msg, count);
>> +    ssif_bmc->is_singlepart_read = (msg.len <= 
>> MAX_PAYLOAD_PER_TRANSACTION);
>> +
>> +    ssif_bmc->response_in_progress = true;
>> +
>> +    /* ssif_bmc not busy */
>> +    ssif_bmc->busy = false;
>> +
>> +    /* Clean old request buffer */
>> +    memset(&ssif_bmc->request, 0, sizeof(struct ipmi_ssif_msg));
>> +exit:
>> +    spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +
>> +    return (ret < 0) ? ret : count;
>> +}
>> +
>> +static int ssif_bmc_open(struct inode *inode, struct file *file)
>> +{
>> +    struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +    int ret = 0;
>> +
>> +    spin_lock_irq(&ssif_bmc->lock);
>> +    if (!ssif_bmc->running)
>> +        ssif_bmc->running = 1;
>> +    else
>> +        ret = -EBUSY;
>> +    spin_unlock_irq(&ssif_bmc->lock);
>> +
>> +    return ret;
>> +}
>> +
>> +static __poll_t ssif_bmc_poll(struct file *file, poll_table *wait)
>> +{
>> +    struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +    __poll_t mask = 0;
>> +
>> +    poll_wait(file, &ssif_bmc->wait_queue, wait);
>> +
>> +    spin_lock_irq(&ssif_bmc->lock);
>> +    /* The request is available, userspace application can get the 
>> request */
>> +    if (ssif_bmc->request_available)
>> +        mask |= POLLIN;
>> +
>> +    spin_unlock_irq(&ssif_bmc->lock);
>> +
>> +    return mask;
>> +}
>> +
>> +static int ssif_bmc_release(struct inode *inode, struct file *file)
>> +{
>> +    struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +
>> +    spin_lock_irq(&ssif_bmc->lock);
>> +    ssif_bmc->running = 0;
>> +    spin_unlock_irq(&ssif_bmc->lock);
>> +
>> +    return 0;
>> +}
>> +
>> +/*
>> + * System calls to device interface for user apps
>> + */
>> +static const struct file_operations ssif_bmc_fops = {
>> +    .owner        = THIS_MODULE,
>> +    .open        = ssif_bmc_open,
>> +    .read        = ssif_bmc_read,
>> +    .write        = ssif_bmc_write,
>> +    .release    = ssif_bmc_release,
>> +    .poll        = ssif_bmc_poll,
>> +};
>> +
>> +/* Called with ssif_bmc->lock held. */
>> +static void complete_response(struct ssif_bmc_ctx *ssif_bmc)
>> +{
>> +    /* Invalidate response in buffer to denote it having been sent. */
>> +    ssif_bmc->response.len = 0;
>> +    ssif_bmc->response_in_progress = false;
>> +    ssif_bmc->nbytes_processed = 0;
>> +    ssif_bmc->remain_len = 0;
>> +    ssif_bmc->busy = false;
>> +    memset(&ssif_bmc->part_buf, 0, sizeof(struct ssif_part_buffer));
>> +    wake_up_all(&ssif_bmc->wait_queue);
>> +}
>> +
>> +static void response_timeout(struct timer_list *t)
>> +{
>> +    struct ssif_bmc_ctx *ssif_bmc = from_timer(ssif_bmc, t, 
>> response_timer);
>> +    unsigned long flags;
>> +
>> +    spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +
>> +    /* Do nothing if the response is in progress */
>> +    if (!ssif_bmc->response_in_progress) {
>> +        /* Recover ssif_bmc from busy */
>> +        ssif_bmc->busy = false;
>> +        ssif_bmc->response_timer_inited = false;
>> +        /* Set aborting flag */
>> +        ssif_bmc->aborting = true;
>> +    }
>> +
>> +    spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +}
>> +
>> +/* Called with ssif_bmc->lock held. */
>> +static void handle_request(struct ssif_bmc_ctx *ssif_bmc)
>> +{
>> +    /* set ssif_bmc to busy waiting for response */
>> +    ssif_bmc->busy = true;
>> +    /* Request message is available to process */
>> +    ssif_bmc->request_available = true;
>> +    /* Clean old response buffer */
>> +    memset(&ssif_bmc->response, 0, sizeof(struct ipmi_ssif_msg));
>> +    /* This is the new READ request.*/
>> +    wake_up_all(&ssif_bmc->wait_queue);
>> +
>> +    /* Armed timer to recover slave from busy state in case of no 
>> response */
>> +    if (!ssif_bmc->response_timer_inited) {
>> +        timer_setup(&ssif_bmc->response_timer, response_timeout, 0);
>> +        ssif_bmc->response_timer_inited = true;
>> +    }
>> +    mod_timer(&ssif_bmc->response_timer, jiffies + 
>> msecs_to_jiffies(RESPONSE_TIMEOUT));
>> +}
>> +
>> +static void calculate_response_part_pec(struct ssif_part_buffer *part)
>> +{
>> +    u8 addr = part->address;
>> +
>> +    /* PEC - Start Read Address */
>> +    part->pec = i2c_smbus_pec(0, &addr, 1);
>> +    /* PEC - SSIF Command */
>> +    part->pec = i2c_smbus_pec(part->pec, &part->smbus_cmd, 1);
>> +    /* PEC - Restart Write Address */
>> +    addr = addr | 0x01;
>> +    part->pec = i2c_smbus_pec(part->pec, &addr, 1);
>> +    part->pec = i2c_smbus_pec(part->pec, &part->length, 1);
>> +    if (part->length)
>> +        part->pec = i2c_smbus_pec(part->pec, part->payload, 
>> part->length);
>> +}
>> +
>> +static void set_singlepart_response_buffer(struct ssif_bmc_ctx 
>> *ssif_bmc)
>> +{
>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +
>> +    part->address = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +    part->length = (u8)ssif_bmc->response.len;
>> +
>> +    /* Clear the rest to 0 */
>> +    memset(part->payload + part->length, 0, 
>> MAX_PAYLOAD_PER_TRANSACTION - part->length);
>> +    memcpy(&part->payload[0], &ssif_bmc->response.payload[0], 
>> part->length);
>> +}
>> +
>> +static void set_multipart_response_buffer(struct ssif_bmc_ctx *ssif_bmc)
>> +{
>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +    u8 part_len = 0;
>> +
>> +    part->address = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +    switch (part->smbus_cmd) {
>> +    case SSIF_IPMI_MULTIPART_READ_START:
>> +        /*
>> +         * Read Start length is 32 bytes.
>> +         * Read Start transfer first 30 bytes of IPMI response
>> +         * and 2 special code 0x00, 0x01.
>> +         */
>> +        ssif_bmc->nbytes_processed = 0;
>> +        ssif_bmc->block_num = 0;
>> +        part->length = MAX_PAYLOAD_PER_TRANSACTION;
>> +        part_len = MAX_IPMI_DATA_PER_START_TRANSACTION;
>> +        ssif_bmc->remain_len = ssif_bmc->response.len - part_len;
>> +
>> +        part->payload[0] = 0x00; /* Start Flag */
>> +        part->payload[1] = 0x01; /* Start Flag */
>> +
>> +        memcpy(&part->payload[2], &ssif_bmc->response.payload[0], 
>> part_len);
>> +        break;
>> +
>> +    case SSIF_IPMI_MULTIPART_READ_MIDDLE:
>> +        /*
>> +         * IPMI READ Middle or READ End messages can carry up to 31 
>> bytes
>> +         * IPMI data plus block number byte.
>> +         */
>> +        if (ssif_bmc->remain_len <= 
>> MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION) {
>> +            /*
>> +             * This is READ End message
>> +             *  Return length is the remaining response data length
>> +             *  plus block number
>> +             *  Block number 0xFF is to indicate this is last message
>> +             *
>> +             */
>> +            /* Clean the buffer */
>> +            memset(&part->payload[0], 0, MAX_PAYLOAD_PER_TRANSACTION);
>> +            part->length = ssif_bmc->remain_len + 1;
>> +            part_len = ssif_bmc->remain_len;
>> +            ssif_bmc->block_num = 0xFF;
>> +            part->payload[0] = ssif_bmc->block_num;
>> +        } else {
>> +            /*
>> +             * This is READ Middle message
>> +             *  Response length is the maximum SMBUS transfer length
>> +             *  Block number byte is incremented
>> +             * Return length is maximum SMBUS transfer length
>> +             */
>> +            part->length = MAX_PAYLOAD_PER_TRANSACTION;
>> +            part_len = MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
>> +            part->payload[0] = ssif_bmc->block_num;
>> +            ssif_bmc->block_num++;
>> +        }
>> +
>> +        ssif_bmc->remain_len -= part_len;
>> +        memcpy(&part->payload[1], ssif_bmc->response.payload + 
>> ssif_bmc->nbytes_processed,
>> +               part_len);
>> +        break;
>> +
>> +    default:
>> +        /* Do not expect to go to this case */
>> +        dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus command 
>> 0x%x\n",
>> +            __func__, part->smbus_cmd);
>> +        break;
>> +    }
>> +
>> +    ssif_bmc->nbytes_processed += part_len;
>> +}
>> +
>> +static bool supported_read_cmd(u8 cmd)
>> +{
>> +    if (cmd == SSIF_IPMI_SINGLEPART_READ ||
>> +        cmd == SSIF_IPMI_MULTIPART_READ_START ||
>> +        cmd == SSIF_IPMI_MULTIPART_READ_MIDDLE)
>> +        return true;
>> +
>> +    return false;
>> +}
>> +
>> +static bool supported_write_cmd(u8 cmd)
>> +{
>> +    if (cmd == SSIF_IPMI_SINGLEPART_WRITE ||
>> +        cmd == SSIF_IPMI_MULTIPART_WRITE_START ||
>> +        cmd == SSIF_IPMI_MULTIPART_WRITE_MIDDLE ||
>> +        cmd == SSIF_IPMI_MULTIPART_WRITE_END)
>> +        return true;
>> +
>> +    return false;
>> +}
>> +
>> +/* Process the IPMI response that will be read by master */
>> +static void handle_read_processed(struct ssif_bmc_ctx *ssif_bmc, u8 
>> *val)
>> +{
>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +
>> +    /* msg_idx start from 0 */
>> +    if (part->index < part->length)
>> +        *val = part->payload[part->index];
>> +    else if (part->index == part->length && ssif_bmc->pec_support)
>> +        *val = part->pec;
>> +    else
>> +        *val = 0;
>> +
>> +    part->index++;
>> +}
>> +
>> +static void handle_write_received(struct ssif_bmc_ctx *ssif_bmc, u8 
>> *val)
>> +{
>> +    /*
>> +     * The msg_idx must be 1 when first enter SSIF_REQ_RECVING state
>> +     * And it would never exceeded 36 bytes included the 32 bytes max 
>> payload +
>> +     * the address + the command + the len and the PEC.
>> +     */
>> +    if (ssif_bmc->msg_idx < 1  || ssif_bmc->msg_idx > MAX_TRANSACTION)
>> +        return;
>> +
>> +    if (ssif_bmc->msg_idx == 1) {
>> +        ssif_bmc->part_buf.length = *val;
>> +        ssif_bmc->part_buf.index = 0;
>> +    } else {
>> +        ssif_bmc->part_buf.payload[ssif_bmc->part_buf.index++] = *val;
>> +    }
>> +
>> +    ssif_bmc->msg_idx++;
>> +}
>> +
>> +static bool validate_request_part(struct ssif_bmc_ctx *ssif_bmc)
>> +{
>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +    bool ret = true;
>> +    u8 cpec;
>> +    u8 addr;
>> +
>> +    if (part->index == part->length) {
>> +        /* PEC is not included */
>> +        ssif_bmc->pec_support = false;
>> +        ret = true;
>> +        goto exit;
>> +    }
>> +
>> +    if (part->index != part->length + 1) {
>> +        ret = false;
>> +        goto exit;
>> +    }
>> +
>> +    /* PEC is included */
>> +    ssif_bmc->pec_support = true;
>> +    part->pec = part->payload[part->length];
>> +    addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +    cpec = i2c_smbus_pec(0, &addr, 1);
>> +    cpec = i2c_smbus_pec(cpec, &part->smbus_cmd, 1);
>> +    cpec = i2c_smbus_pec(cpec, &part->length, 1);
>> +    /*
>> +     * As SMBus specification does not allow the length
>> +     * (byte count) in the Write-Block protocol to be zero.
>> +     * Therefore, it is illegal to have the last Middle
>> +     * transaction in the sequence carry 32-byte and have
>> +     * a length of ‘0’ in the End transaction.
>> +     * But some users may try to use this way and we should
>> +     * prevent ssif_bmc driver broken in this case.
>> +     */
>> +    if (part->length)
>> +        cpec = i2c_smbus_pec(cpec, part->payload, part->length);
>> +
>> +    if (cpec != part->pec)
>> +        ret = false;
>> +
>> +exit:
>> +    return ret;
>> +}
>> +
>> +static void process_request_part(struct ssif_bmc_ctx *ssif_bmc)
>> +{
>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +    unsigned int len;
>> +
>> +    switch (part->smbus_cmd) {
>> +    case SSIF_IPMI_SINGLEPART_WRITE:
>> +        /* save the whole part to request*/
>> +        ssif_bmc->request.len = part->length;
>> +        memcpy(ssif_bmc->request.payload, part->payload, part->length);
>> +
>> +        break;
>> +    case SSIF_IPMI_MULTIPART_WRITE_START:
>> +        ssif_bmc->request.len = 0;
>> +
>> +        fallthrough;
>> +    case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
>> +    case SSIF_IPMI_MULTIPART_WRITE_END:
>> +        len = ssif_bmc->request.len + part->length;
>> +        /* Do the bound check here, not allow the request len exceed 
>> 254 bytes */
>> +        if (len > IPMI_SSIF_PAYLOAD_MAX) {
>> +            dev_warn(&ssif_bmc->client->dev,
>> +                 "Warn: Request exceeded 254 bytes, aborting");
>> +            /* Request too long, aborting */
>> +            ssif_bmc->aborting =  true;
>> +        } else {
>> +            memcpy(ssif_bmc->request.payload + ssif_bmc->request.len,
>> +                   part->payload, part->length);
>> +            ssif_bmc->request.len += part->length;
>> +        }
>> +        break;
>> +    default:
>> +        /* Do not expect to go to this case */
>> +        dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus command 
>> 0x%x\n",
>> +            __func__, part->smbus_cmd);
>> +        break;
>> +    }
>> +}
>> +
>> +static void process_smbus_cmd(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +    /* SMBUS command can vary (single or multi-part) */
>> +    ssif_bmc->part_buf.smbus_cmd = *val;
>> +    ssif_bmc->msg_idx = 1;
>> +    memset(&ssif_bmc->part_buf.payload[0], 0, 
>> MAX_PAYLOAD_PER_TRANSACTION);
>> +
>> +    if (*val == SSIF_IPMI_SINGLEPART_WRITE || *val == 
>> SSIF_IPMI_MULTIPART_WRITE_START) {
>> +        /*
>> +         * The response maybe not come in-time, causing host SSIF driver
>> +         * to timeout and resend a new request. In such case check for
>> +         * pending response and clear it
>> +         */
>> +        if (ssif_bmc->response_in_progress)
>> +            complete_response(ssif_bmc);
>> +
>> +        /* This is new request, flip aborting flag if set */
>> +        if (ssif_bmc->aborting)
>> +            ssif_bmc->aborting = false;
>> +    }
>> +}
>> +
>> +static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 
>> *val)
>> +{
>> +    if (ssif_bmc->state == SSIF_READY ||
> Is this actually correct? The state machine seems to set this as the 
> default state and in my testing we seem to always reach here with the 
> state == SSIF_READY?

The I2C_SLAVE_READ_REQUESTED event is expected to come on SSIF_SMBUS_CMD 
state where Slave has already received and validated the SMBus command, 
in this case is the I2C_SLAVE_READ_REQUESTED event if the SMBus command 
indeed is the READ command. You can see the check supported_read_cmd() 
below.

If Slave see the I2C_SLAVE_READ_REQUESTED event on other states, it will 
transition to SSIF_ABORTING state that discard everything until there is 
a new transaction come.

On READ, the sequence of Slave event should be as below:
I2C_SLAVE_WRITE_REQUESTED (addr) => I2C_SLAVE_WRITE_RECEIVED (SMBus cmd) 
=> I2C_SLAVE_READ_REQUESTED (Slave feed the first byte) => 
I2C_SLAVE_READ_PROCESSED (Slave 2nd byte) => .... => I2C_SLAVE_STOP

>> +        ssif_bmc->state == SSIF_START ||
>> +        ssif_bmc->state == SSIF_REQ_RECVING ||
>> +        ssif_bmc->state == SSIF_RES_SENDING) {
>> +        dev_warn(&ssif_bmc->client->dev,
>> +             "Warn: %s unexpected READ REQUESTED in state=%s\n",
>> +             __func__, state_to_string(ssif_bmc->state));
>> +        ssif_bmc->state = SSIF_ABORTING;
>> +        *val = 0;
>> +        return;
>> +
>> +    } else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +        if (!supported_read_cmd(ssif_bmc->part_buf.smbus_cmd)) {
>> +            dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus 
>> read command=0x%x",
>> +                 ssif_bmc->part_buf.smbus_cmd);
>> +            ssif_bmc->aborting = true;
>> +        }
>> +
>> +        if (ssif_bmc->aborting)
>> +            ssif_bmc->state = SSIF_ABORTING;
>> +        else
>> +            ssif_bmc->state = SSIF_RES_SENDING;
>> +    }
>> +
>> +    ssif_bmc->msg_idx = 0;
>> +
>> +    /* Send 0 if there is nothing to send */
>> +    if (!ssif_bmc->response_in_progress || ssif_bmc->state == 
>> SSIF_ABORTING) {
>> +        *val = 0;
>> +        return;
>> +    }
>> +
>> +    if (ssif_bmc->is_singlepart_read)
>> +        set_singlepart_response_buffer(ssif_bmc);
>> +    else
>> +        set_multipart_response_buffer(ssif_bmc);
>> +
>> +    calculate_response_part_pec(&ssif_bmc->part_buf);
>> +    ssif_bmc->part_buf.index = 0;
>> +    *val = ssif_bmc->part_buf.length;
>> +}
>> +
>> +static void on_read_processed_event(struct ssif_bmc_ctx *ssif_bmc, u8 
>> *val)
>> +{
>> +    if (ssif_bmc->state == SSIF_READY ||
> Same comment as above?

Same here, I2C_SLAVE_READ_PROCESSED is expected to come after the 
I2C_SLAVE_READ_REQUESTED or other I2C_SLAVE_READ_PROCESSED. ie: when the 
state is SSIF_RES_SENDING.
If it comes when Slave in states other than SSIF_RES_SENDING, the Slave 
will transition to SSIF_ABORTING state.

>> +        ssif_bmc->state == SSIF_START ||
>> +        ssif_bmc->state == SSIF_REQ_RECVING ||
>> +        ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +        dev_warn(&ssif_bmc->client->dev,
>> +             "Warn: %s unexpected READ PROCESSED in state=%s\n",
>> +             __func__, state_to_string(ssif_bmc->state));
>> +        ssif_bmc->state = SSIF_ABORTING;
>> +        *val = 0;
>> +        return;
>> +    }
>> +
>> +    /* Send 0 if there is nothing to send */
>> +    if (!ssif_bmc->response_in_progress || ssif_bmc->state == 
>> SSIF_ABORTING) {
>> +        *val = 0;
>> +        return;
>> +    }
>> +
>> +    handle_read_processed(ssif_bmc, val);
>> +}
>> +
>> +static void on_write_requested_event(struct ssif_bmc_ctx *ssif_bmc, 
>> u8 *val)
>> +{
>> +    if (ssif_bmc->state == SSIF_READY || ssif_bmc->state == 
>> SSIF_SMBUS_CMD) {
>> +        ssif_bmc->state = SSIF_START;
>> +
>> +    } else if (ssif_bmc->state == SSIF_START ||
>> +           ssif_bmc->state == SSIF_REQ_RECVING ||
>> +           ssif_bmc->state == SSIF_RES_SENDING) {
>> +        dev_warn(&ssif_bmc->client->dev,
>> +             "Warn: %s unexpected WRITE REQUEST in state=%s\n",
>> +             __func__, state_to_string(ssif_bmc->state));
>> +        ssif_bmc->state = SSIF_ABORTING;
>> +        return;
>> +    }
>> +
>> +    ssif_bmc->msg_idx = 0;
>> +    ssif_bmc->part_buf.address = *val;
>> +}
>> +
>> +static void on_write_received_event(struct ssif_bmc_ctx *ssif_bmc, u8 
>> *val)
>> +{
>> +    if (ssif_bmc->state == SSIF_READY ||
>> +        ssif_bmc->state == SSIF_RES_SENDING) {
>> +        dev_warn(&ssif_bmc->client->dev,
>> +             "Warn: %s unexpected WRITE RECEIVED in state=%s\n",
>> +             __func__, state_to_string(ssif_bmc->state));
>> +        ssif_bmc->state = SSIF_ABORTING;
>> +
>> +    } else if (ssif_bmc->state == SSIF_START) {
>> +        ssif_bmc->state = SSIF_SMBUS_CMD;
>> +
>> +    } else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +        if (!supported_write_cmd(ssif_bmc->part_buf.smbus_cmd)) {
>> +            dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus 
>> write command=0x%x",
>> +                 ssif_bmc->part_buf.smbus_cmd);
>> +            ssif_bmc->aborting = true;
>> +        }
>> +
>> +        if (ssif_bmc->aborting)
>> +            ssif_bmc->state = SSIF_ABORTING;
>> +        else
>> +            ssif_bmc->state = SSIF_REQ_RECVING;
>> +    }
>> +
>> +    /* This is response sending state */
>> +    if (ssif_bmc->state == SSIF_REQ_RECVING)
>> +        handle_write_received(ssif_bmc, val);
>> +    else if (ssif_bmc->state == SSIF_SMBUS_CMD)
>> +        process_smbus_cmd(ssif_bmc, val);
>> +}
>> +
>> +static void on_stop_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +    if (ssif_bmc->state == SSIF_READY ||
>> +        ssif_bmc->state == SSIF_START ||
>> +        ssif_bmc->state == SSIF_SMBUS_CMD ||
>> +        ssif_bmc->state == SSIF_ABORTING) {
>> +        dev_warn(&ssif_bmc->client->dev,
>> +             "Warn: %s unexpected SLAVE STOP in state=%s\n",
>> +             __func__, state_to_string(ssif_bmc->state));
>> +        ssif_bmc->state = SSIF_READY;
>> +
>> +    } else if (ssif_bmc->state == SSIF_REQ_RECVING) {
>> +        if (validate_request_part(ssif_bmc)) {
>> +            process_request_part(ssif_bmc);
>> +            if (ssif_bmc->part_buf.smbus_cmd == 
>> SSIF_IPMI_SINGLEPART_WRITE ||
>> +                ssif_bmc->part_buf.smbus_cmd == 
>> SSIF_IPMI_MULTIPART_WRITE_END)
>> +                handle_request(ssif_bmc);
>> +            ssif_bmc->state = SSIF_READY;
>> +        } else {
>> +            /*
>> +             * A BMC that receives an invalid request drop the data 
>> for the write
>> +             * transaction and any further transactions (read or 
>> write) until
>> +             * the next valid read or write Start transaction is 
>> received
>> +             */
>> +            dev_err(&ssif_bmc->client->dev, "Error: invalid pec\n");
>> +            ssif_bmc->aborting = true;
>> +        }
>> +    } else if (ssif_bmc->state == SSIF_RES_SENDING) {
>> +        if (ssif_bmc->is_singlepart_read || ssif_bmc->block_num == 0xFF)
>> +            /* Invalidate response buffer to denote it is sent */
>> +            complete_response(ssif_bmc);
>> +        ssif_bmc->state = SSIF_READY;
>> +    }
>> +
>> +    /* Reset message index */
>> +    ssif_bmc->msg_idx = 0;
>> +}
>> +
>> +/*
>> + * Callback function to handle I2C slave events
>> + */
>> +static int ssif_bmc_cb(struct i2c_client *client, enum 
>> i2c_slave_event event, u8 *val)
>> +{
>> +    unsigned long flags;
>> +    struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
>> +    int ret = 0;
>> +
>> +    spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +
>> +    switch (event) {
>> +    case I2C_SLAVE_READ_REQUESTED:
>> +        on_read_requested_event(ssif_bmc, val);
>> +        break;
>> +
>> +    case :
>> +        on_write_requested_event(ssif_bmc, val);
>> +        break;
>> +
>> +    case I2C_SLAVE_READ_PROCESSED:
>> +        on_read_processed_event(ssif_bmc, val);
>> +        break;
>> +
>> +    case I2C_SLAVE_WRITE_RECEIVED:
>> +        on_write_received_event(ssif_bmc, val);
>> +        break;
>> +
>> +    case I2C_SLAVE_STOP:
>> +        on_stop_event(ssif_bmc, val);
>> +        break;
>> +
>> +    default:
>> +        dev_warn(&ssif_bmc->client->dev, "Warn: Unknown i2c slave 
>> event\n");
>> +        break;
>> +    }
>> +
>> +    if (!ssif_bmc->aborting && ssif_bmc->busy)
>> +        ret = -EBUSY;
>> +
>> +    spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +
>> +    return ret;
>> +}
>> +
>> +static int ssif_bmc_probe(struct i2c_client *client, const struct 
>> i2c_device_id *id)
>> +{
>> +    struct ssif_bmc_ctx *ssif_bmc;
>> +    int ret;
>> +
>> +    ssif_bmc = devm_kzalloc(&client->dev, sizeof(*ssif_bmc), 
>> GFP_KERNEL);
>> +    if (!ssif_bmc)
>> +        return -ENOMEM;
>> +
>> +    spin_lock_init(&ssif_bmc->lock);
>> +
>> +    init_waitqueue_head(&ssif_bmc->wait_queue);
>> +    ssif_bmc->request_available = false;
>> +    ssif_bmc->response_in_progress = false;
>> +    ssif_bmc->busy = false;
>> +    ssif_bmc->response_timer_inited = false;
>> +
>> +    /* Register misc device interface */
>> +    ssif_bmc->miscdev.minor = MISC_DYNAMIC_MINOR;
>> +    ssif_bmc->miscdev.name = DEVICE_NAME;
>> +    ssif_bmc->miscdev.fops = &ssif_bmc_fops;
>> +    ssif_bmc->miscdev.parent = &client->dev;
>> +    ret = misc_register(&ssif_bmc->miscdev);
>> +    if (ret)
>> +        return ret;
>> +
>> +    ssif_bmc->client = client;
>> +    ssif_bmc->client->flags |= I2C_CLIENT_SLAVE;
>> +
>> +    /* Register I2C slave */
>> +    i2c_set_clientdata(client, ssif_bmc);
>> +    ret = i2c_slave_register(client, ssif_bmc_cb);
>> +    if (ret)
>> +        misc_deregister(&ssif_bmc->miscdev);
>> +
>> +    return ret;
>> +}
>> +
>> +static void ssif_bmc_remove(struct i2c_client *client)
>> +{
>> +    struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
>> +
>> +    i2c_slave_unregister(client);
>> +    misc_deregister(&ssif_bmc->miscdev);
>> +}
>> +
>> +static const struct of_device_id ssif_bmc_match[] = {
>> +    { .compatible = "ssif-bmc" },
>> +    { },
>> +};
>> +MODULE_DEVICE_TABLE(of, ssif_bmc_match);
>> +
>> +static const struct i2c_device_id ssif_bmc_id[] = {
>> +    { DEVICE_NAME, 0 },
>> +    { },
>> +};
>> +MODULE_DEVICE_TABLE(i2c, ssif_bmc_id);
>> +
>> +static struct i2c_driver ssif_bmc_driver = {
>> +    .driver         = {
>> +        .name           = DEVICE_NAME,
>> +        .of_match_table = ssif_bmc_match,
>> +    },
>> +    .probe          = ssif_bmc_probe,
>> +    .remove         = ssif_bmc_remove,
>> +    .id_table       = ssif_bmc_id,
>> +};
>> +
>> +module_i2c_driver(ssif_bmc_driver);
>> +
>> +MODULE_AUTHOR("Quan Nguyen <quan@os.amperecomputing.com>");
>> +MODULE_AUTHOR("Chuong Tran <chuong@os.amperecomputing.com>");
>> +MODULE_DESCRIPTION("Linux device driver of the BMC IPMI SSIF 
>> interface.");
>> +MODULE_LICENSE("GPL");
>> diff --git a/include/uapi/linux/ipmi_ssif_bmc.h 
>> b/include/uapi/linux/ipmi_ssif_bmc.h
>> new file mode 100644
>> index 000000000000..1c6a753dad08
>> --- /dev/null
>> +++ b/include/uapi/linux/ipmi_ssif_bmc.h
>> @@ -0,0 +1,18 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only WITH Linux-syscall-note*/
>> +/*
>> + * Copyright (c) 2022, Ampere Computing LLC.
>> + */
>> +
>> +#ifndef _UAPI_LINUX_IPMI_SSIF_BMC_H
>> +#define _UAPI_LINUX_IPMI_SSIF_BMC_H
>> +
>> +#include <linux/types.h>
>> +
>> +/* Max length of ipmi ssif message included netfn and cmd field */
>> +#define IPMI_SSIF_PAYLOAD_MAX         254
>> +struct ipmi_ssif_msg {
>> +    unsigned int len;
>> +    __u8    payload[IPMI_SSIF_PAYLOAD_MAX];
>> +};
>> +
>> +#endif /* _UAPI_LINUX_IPMI_SSIF_BMC_H */

On 10/10/2022 02:28, Quan Nguyen wrote:
>
>
> On 07/10/2022 20:26, Graeme Gregory wrote:
>>
>> On 04/10/2022 10:31, Quan Nguyen wrote:
>>> The SMBus system interface (SSIF) IPMI BMC driver can be used to 
>>> perform
>>> in-band IPMI communication with their host in management (BMC) side.
>>>
>>> Thanks Dan for the copy_from_user() fix in the link below.
>>>
>>> Link: 
>>> https://lore.kernel.org/linux-arm-kernel/20220310114119.13736-4-quan@os.amperecomputing.com/
>>> Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
>>
>> I have been testing this on our hardware and I don't seem to be able 
>> to get this driver working. I was using an older version.
>>
>> I have hacked ssifbridged to deal with the change in len from u8 to 
>> unsigned int.
>>
>> It works as long as I only ever send SSIF commands, any attempt to 
>> read a response crashes the state machine and the driver never 
>> recovers. No further SSIF comms is possible! (slave doesnt even ACK 
>> writes).
>>
>> A couple of comments below on possible state machine errors.
>>
>> Its possible I am doing something wrong!
>>
>
> Thanks Graeme for the test and the comments.
>
> What's your testing hardware?
>
> This was tested with Aspeed ast2500 and ast2600 with the patch series 
> [1] below applied.
>
> If you use the same hw, could you pick the series and see if any thing 
> improve ?
>
> [1] 
> https://lore.kernel.org/all/20210616031046.2317-1-quan@os.amperecomputing.com/
>
Thanks, that patch series does stop the state machine crashing.

I am testing on AST2600EVB with A1 rev, but we also have our own DC-SCM 
with A3 chip.

Responses are still not working for me, but I think that may be an error 
in my ssifbridged hacks.

Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c ssifbridged[335]: Read ssif 
request message with len=13 netfn=44 lun=0 cmd=2

Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c ipmid[312]: BootCode: 
000000000000000000

Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c ssifbridged[335]: Send ssif 
respond message with len=4 netfn=45 lun=0 cmd=2 cc=0

Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c kernel: ipmi-ssif-host 
0-0010: Warn: on_read_requested_event unexpected READ REQUESTED in 
state=SSIF_READY

Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c kernel: ipmi-ssif-host 
0-0010: Warn: on_stop_event unexpected SLAVE STOP in state=SSIF_ABORTING

>>> ---
>>> v10:
>>>    + None
>>>
>>> v9:
>>>    + Fix dependence with I2C subsystem                            
>>> [Randy]
>>>    + Remove useless error handling path                              
>>> [CJ]
>>>    + Update comment for SSIF_ABORTING state                          
>>> [CJ]
>>>    + Fix "unknown type name --u8"                     [kernel test 
>>> robot]
>>>    + Fix ssif_bmc_remove() to return void to align with recent kernel
>>> change [Quan]
>>>
>>> v8:
>>>    + Dropped ssif_bmc.h file and move its content to ssif_bmc.c   
>>> [Corey]
>>>    + Add struct ipmi_ssif_msg to include/uapi/linux/ipmi_ssif_bmc.h
>>>    header file [Corey]
>>>    + Use unsigned int for len field in struct ipmi_ssif_msg       
>>> [Corey]
>>>    + Avoid using packed structure                                 
>>> [Corey]
>>>    + Add comment to clarify the logic flow                        
>>> [Corey]
>>>    + Fix multipart read end with len=0 issue                      
>>> [Corey]
>>>    + Refactor code handle the too big request message             
>>> [Corey]
>>>    + Fix code indentation issue                                   
>>> [Corey]
>>>    + Clean buffer before receiving request to avoid garbage        
>>> [Quan]
>>>    + Fix the license to SPDX-License-Identifier: GPL-2.0-only      
>>> [Quan]
>>>
>>> v7:
>>>    + Remove unneccessary del_timer() in response_timeout()        
>>> [Corey]
>>>    + Change compatible string from "ampere,ssif-bmc" to "ssif-bmc"  
>>> [Jae]
>>>    + Add MODULE_DEVICE_TABLE(of, ssif_bmc_match), fix blank line    
>>> [Jae]
>>>    + Dropped the use of ssif_msg_len() macro, use the len directly 
>>> [Quan]
>>>    + Solve possible issue if both response timer and ssif_bmc_write()
>>>    occurred at the same time                                      
>>> [Corey]
>>>    + Fix wrong return type of ssif_bmc_poll()         [kernel robot 
>>> test]
>>>    + Refactor and introduce ssif_part_buffer struct to replace the
>>>    response_buf to manage each send/receive part of ssif           
>>> [Quan]
>>>    + Change SSIF_BAD_SMBUS state to SSIF_ABORTING state           
>>> [Corey]
>>>    + Support abort feature to skip the current bad request/response and
>>>    wait until next new request                                    
>>> [Corey]
>>>    + Refactor the PEC calculation to avoid the re-calculate the PEC on
>>>    each I2C_SLAVE_WRITE_RECEIVED event                             
>>> [Quan]
>>>    + Fix the use of error-proned idx                              
>>> [Corey]
>>>    + Defer the test for valid SMBus command until the read/write part
>>>    is determined [Quan]
>>>    + Change/split unsupported_smbus_cmd() to
>>> supported_[write|read]_cmd() [Corey]
>>>    + Abort the request if somehow its size exceeded 255 bytes      
>>> [Quan]
>>>
>>> v6:
>>>    + Drop the use of slave_enable()                             
>>> [Wolfram]
>>>    + Make i2c-aspeed to issue RxCmdLast command on all
>>>    I2C_SLAVE_WRITE_REQUESTED event to assert NAK when slave busy   
>>> [Quan]
>>>    + Make i2c slave to return -EBUSY when it's busy                
>>> [Quan]
>>>    + Drop the aborting feature as return Completion Code 0xFF may stop
>>>    host to retry and make ipmi_ssif.so fails to load               
>>> [Quan]
>>>    + Add timer to recover slave from busy state when no response   
>>> [Quan]
>>>    + Clean request/response buffer appropriately                   
>>> [Quan]
>>>    + Add some minor change on error and warning messages           
>>> [Quan]
>>>
>>> v5:
>>>    + None
>>>
>>> v4:
>>>    + Send response with Completion code 0xFF when aborting         
>>> [Quan]
>>>    + Added bounding check on SMBus writes and the whole request     
>>> [Dan]
>>>    + Moved buffer to end of struct ssif_bmc_ctx to avoid context
>>>      corruption if somehow buffer is written past the end           
>>> [Dan]
>>>    + Return -EINVAL if userspace buffer too small, dont
>>>      silence truncate [Corey, Joel]
>>>    + Not necessary to check NONBLOCK in lock                      
>>> [Corey]
>>>    + Enforce one user at a time                                    
>>> [Joel]
>>>    + Reject write with invalid response length from userspace     
>>> [Corey]
>>>    + Add state machines for better ssif bmc state handling         
>>> [Quan]
>>>    + Drop ssif_bmc_aspeed.c and make ssif_bmc.c is generic
>>>      SSIF BMC driver                                               
>>> [Quan]
>>>    + Change compatible string "aspeed,ast2500-ssif-bmc" to
>>> "ampere,ssif-bmc" [Quan]
>>>    + Abort current request with invalid SMBus write or
>>>      invalid command                                               
>>> [Quan]
>>>    + Abort all request if there is pending response                
>>> [Quan]
>>>    + Changed validate_pec() to validate_request()                  
>>> [Quan]
>>>    + Add unsupported_smbus_cmd() to handle unknown SMBus command   
>>> [Quan]
>>>    + Print internal state string for ease investigating issue      
>>> [Quan]
>>>    + Move to READY state on SLAVE_STOP event                       
>>> [Quan]
>>>    + Change initilize_transfer() to process_smbus_cmd()            
>>> [Quan]
>>>    + Introduce functions for each slave event                      
>>> [Quan]
>>>
>>> v3:
>>>    + Removed redundant license info                                
>>> [Joel]
>>>    + Switched to use traditional if-else                           
>>> [Joel]
>>>    + Removed unused ssif_bmc_ioctl()                               
>>> [Joel]
>>>    + Made handle_request()/complete_response() to return void      
>>> [Joel]
>>>    + Refactored send_ssif_bmc_response() and
>>> receive_ssif_bmc_request() [Corey]
>>>    + Removed mutex                                                
>>> [Corey]
>>>    + Use spin_lock/unlock_irqsave/restore in callback             
>>> [Corey]
>>>    + Removed the unnecessary memset                               
>>> [Corey]
>>>    + Switch to use dev_err()                                      
>>> [Corey]
>>>
>>> v2:
>>>    + Fixed compiling error with COMPILE_TEST for arc
>>> ---
>>>   drivers/char/ipmi/Kconfig          |  10 +
>>>   drivers/char/ipmi/Makefile         |   1 +
>>>   drivers/char/ipmi/ssif_bmc.c       | 873 
>>> +++++++++++++++++++++++++++++
>>>   include/uapi/linux/ipmi_ssif_bmc.h |  18 +
>>>   4 files changed, 902 insertions(+)
>>>   create mode 100644 drivers/char/ipmi/ssif_bmc.c
>>>   create mode 100644 include/uapi/linux/ipmi_ssif_bmc.h
>>>
>>> diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig
>>> index 39565cf74b2c..b6c0d35fc1a5 100644
>>> --- a/drivers/char/ipmi/Kconfig
>>> +++ b/drivers/char/ipmi/Kconfig
>>> @@ -169,6 +169,16 @@ config ASPEED_BT_IPMI_BMC
>>>         found on Aspeed SOCs (AST2400 and AST2500). The driver
>>>         implements the BMC side of the BT interface.
>>> +config SSIF_IPMI_BMC
>>> +    tristate "SSIF IPMI BMC driver"
>>> +    depends on I2C && I2C_SLAVE
>>> +    help
>>> +      This enables the IPMI SMBus system interface (SSIF) at the
>>> +      management (BMC) side.
>>> +
>>> +      The driver implements the BMC side of the SMBus system
>>> +      interface (SSIF).
>>> +
>>>   config IPMB_DEVICE_INTERFACE
>>>       tristate 'IPMB Interface handler'
>>>       depends on I2C
>>> diff --git a/drivers/char/ipmi/Makefile b/drivers/char/ipmi/Makefile
>>> index 7ce790efad92..cb6138b8ded9 100644
>>> --- a/drivers/char/ipmi/Makefile
>>> +++ b/drivers/char/ipmi/Makefile
>>> @@ -30,3 +30,4 @@ obj-$(CONFIG_ASPEED_BT_IPMI_BMC) += bt-bmc.o
>>>   obj-$(CONFIG_ASPEED_KCS_IPMI_BMC) += kcs_bmc_aspeed.o
>>>   obj-$(CONFIG_NPCM7XX_KCS_IPMI_BMC) += kcs_bmc_npcm7xx.o
>>>   obj-$(CONFIG_IPMB_DEVICE_INTERFACE) += ipmb_dev_int.o
>>> +obj-$(CONFIG_SSIF_IPMI_BMC) += ssif_bmc.o
>>> diff --git a/drivers/char/ipmi/ssif_bmc.c 
>>> b/drivers/char/ipmi/ssif_bmc.c
>>> new file mode 100644
>>> index 000000000000..a7bb4b99000e
>>> --- /dev/null
>>> +++ b/drivers/char/ipmi/ssif_bmc.c
>>> @@ -0,0 +1,873 @@
>>> +// SPDX-License-Identifier: GPL-2.0-only
>>> +/*
>>> + * The driver for BMC side of SSIF interface
>>> + *
>>> + * Copyright (c) 2022, Ampere Computing LLC
>>> + *
>>> + */
>>> +
>>> +#include <linux/i2c.h>
>>> +#include <linux/miscdevice.h>
>>> +#include <linux/module.h>
>>> +#include <linux/of.h>
>>> +#include <linux/platform_device.h>
>>> +#include <linux/poll.h>
>>> +#include <linux/sched.h>
>>> +#include <linux/mutex.h>
>>> +#include <linux/spinlock.h>
>>> +#include <linux/timer.h>
>>> +#include <linux/jiffies.h>
>>> +#include <linux/ipmi_ssif_bmc.h>
>>> +
>>> +#define DEVICE_NAME "ipmi-ssif-host"
>>> +
>>> +#define GET_8BIT_ADDR(addr_7bit)                (((addr_7bit) << 1) 
>>> & 0xff)
>>> +
>>> +/* A standard SMBus Transaction is limited to 32 data bytes */
>>> +#define MAX_PAYLOAD_PER_TRANSACTION             32
>>> +/* Transaction includes the address, the command, the length and 
>>> the PEC byte */
>>> +#define MAX_TRANSACTION (MAX_PAYLOAD_PER_TRANSACTION + 4)
>>> +
>>> +#define MAX_IPMI_DATA_PER_START_TRANSACTION     30
>>> +#define MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION    31
>>> +
>>> +#define SSIF_IPMI_SINGLEPART_WRITE              0x2
>>> +#define SSIF_IPMI_SINGLEPART_READ               0x3
>>> +#define SSIF_IPMI_MULTIPART_WRITE_START         0x6
>>> +#define SSIF_IPMI_MULTIPART_WRITE_MIDDLE        0x7
>>> +#define SSIF_IPMI_MULTIPART_WRITE_END           0x8
>>> +#define SSIF_IPMI_MULTIPART_READ_START          0x3
>>> +#define SSIF_IPMI_MULTIPART_READ_MIDDLE         0x9
>>> +
>>> +/*
>>> + * IPMI 2.0 Spec, section 12.7 SSIF Timing,
>>> + * Request-to-Response Time is T6max(250ms) - T1max(20ms) - 3ms = 
>>> 227ms
>>> + * Recover ssif_bmc from busy state if it takes up to 500ms
>>> + */
>>> +#define RESPONSE_TIMEOUT                        500 /* ms */
>>> +
>>> +struct ssif_part_buffer {
>>> +    u8 address;
>>> +    u8 smbus_cmd;
>>> +    u8 length;
>>> +    u8 payload[MAX_PAYLOAD_PER_TRANSACTION];
>>> +    u8 pec;
>>> +    u8 index;
>>> +};
>>> +
>>> +/*
>>> + * SSIF internal states:
>>> + *   SSIF_READY         0x00 : Ready state
>>> + *   SSIF_START         0x01 : Start smbus transaction
>>> + *   SSIF_SMBUS_CMD     0x02 : Received SMBus command
>>> + *   SSIF_REQ_RECVING   0x03 : Receiving request
>>> + *   SSIF_RES_SENDING   0x04 : Sending response
>>> + *   SSIF_ABORTING      0x05 : Aborting state
>>> + */
>>> +enum ssif_state {
>>> +    SSIF_READY,
>>> +    SSIF_START,
>>> +    SSIF_SMBUS_CMD,
>>> +    SSIF_REQ_RECVING,
>>> +    SSIF_RES_SENDING,
>>> +    SSIF_ABORTING,
>>> +    SSIF_STATE_MAX
>>> +};
>>> +
>>> +struct ssif_bmc_ctx {
>>> +    struct i2c_client       *client;
>>> +    struct miscdevice       miscdev;
>>> +    int                     msg_idx;
>>> +    bool                    pec_support;
>>> +    /* ssif bmc spinlock */
>>> +    spinlock_t              lock;
>>> +    wait_queue_head_t       wait_queue;
>>> +    u8                      running;
>>> +    enum ssif_state         state;
>>> +    /* Timeout waiting for response */
>>> +    struct timer_list       response_timer;
>>> +    bool                    response_timer_inited;
>>> +    /* Flag to identify a Multi-part Read Transaction */
>>> +    bool                    is_singlepart_read;
>>> +    u8                      nbytes_processed;
>>> +    u8                      remain_len;
>>> +    u8                      recv_len;
>>> +    /* Block Number of a Multi-part Read Transaction */
>>> +    u8                      block_num;
>>> +    bool                    request_available;
>>> +    bool                    response_in_progress;
>>> +    bool                    busy;
>>> +    bool                    aborting;
>>> +    /* Buffer for SSIF Transaction part*/
>>> +    struct ssif_part_buffer part_buf;
>>> +    struct ipmi_ssif_msg    response;
>>> +    struct ipmi_ssif_msg    request;
>>> +};
>>> +
>>> +static inline struct ssif_bmc_ctx *to_ssif_bmc(struct file *file)
>>> +{
>>> +    return container_of(file->private_data, struct ssif_bmc_ctx, 
>>> miscdev);
>>> +}
>>> +
>>> +static const char *state_to_string(enum ssif_state state)
>>> +{
>>> +    switch (state) {
>>> +    case SSIF_READY:
>>> +        return "SSIF_READY";
>>> +    case SSIF_START:
>>> +        return "SSIF_START";
>>> +    case SSIF_SMBUS_CMD:
>>> +        return "SSIF_SMBUS_CMD";
>>> +    case SSIF_REQ_RECVING:
>>> +        return "SSIF_REQ_RECVING";
>>> +    case SSIF_RES_SENDING:
>>> +        return "SSIF_RES_SENDING";
>>> +    case SSIF_ABORTING:
>>> +        return "SSIF_ABORTING";
>>> +    default:
>>> +        return "SSIF_STATE_UNKNOWN";
>>> +    }
>>> +}
>>> +
>>> +/* Handle SSIF message that will be sent to user */
>>> +static ssize_t ssif_bmc_read(struct file *file, char __user *buf, 
>>> size_t count, loff_t *ppos)
>>> +{
>>> +    struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>>> +    struct ipmi_ssif_msg msg;
>>> +    unsigned long flags;
>>> +    ssize_t ret;
>>> +
>>> +    spin_lock_irqsave(&ssif_bmc->lock, flags);
>>> +    while (!ssif_bmc->request_available) {
>>> +        spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>>> +        if (file->f_flags & O_NONBLOCK)
>>> +            return -EAGAIN;
>>> +        ret = wait_event_interruptible(ssif_bmc->wait_queue,
>>> +                           ssif_bmc->request_available);
>>> +        if (ret)
>>> +            return ret;
>>> +        spin_lock_irqsave(&ssif_bmc->lock, flags);
>>> +    }
>>> +
>>> +    if (count < min_t(ssize_t,
>>> +              sizeof_field(struct ipmi_ssif_msg, len) + 
>>> ssif_bmc->request.len,
>>> +              sizeof(struct ipmi_ssif_msg))) {
>>> +        spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>>> +        ret = -EINVAL;
>>> +    } else {
>>> +        count = min_t(ssize_t,
>>> +                  sizeof_field(struct ipmi_ssif_msg, len) + 
>>> ssif_bmc->request.len,
>>> +                  sizeof(struct ipmi_ssif_msg));
>>> +        memcpy(&msg, &ssif_bmc->request, count);
>>> +        ssif_bmc->request_available = false;
>>> +        spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>>> +
>>> +        ret = copy_to_user(buf, &msg, count);
>>> +    }
>>> +
>>> +    return (ret < 0) ? ret : count;
>>> +}
>>> +
>>> +/* Handle SSIF message that is written by user */
>>> +static ssize_t ssif_bmc_write(struct file *file, const char __user 
>>> *buf, size_t count,
>>> +                  loff_t *ppos)
>>> +{
>>> +    struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>>> +    struct ipmi_ssif_msg msg;
>>> +    unsigned long flags;
>>> +    ssize_t ret;
>>> +
>>> +    if (count > sizeof(struct ipmi_ssif_msg))
>>> +        return -EINVAL;
>>> +
>>> +    if (copy_from_user(&msg, buf, count))
>>> +        return -EFAULT;
>>> +
>>> +    if (!msg.len || count < sizeof_field(struct ipmi_ssif_msg, len) 
>>> + msg.len)
>>> +        return -EINVAL;
>>> +
>>> +    spin_lock_irqsave(&ssif_bmc->lock, flags);
>>> +    while (ssif_bmc->response_in_progress) {
>>> +        spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>>> +        if (file->f_flags & O_NONBLOCK)
>>> +            return -EAGAIN;
>>> +        ret = wait_event_interruptible(ssif_bmc->wait_queue,
>>> + !ssif_bmc->response_in_progress);
>>> +        if (ret)
>>> +            return ret;
>>> +        spin_lock_irqsave(&ssif_bmc->lock, flags);
>>> +    }
>>> +
>>> +    /*
>>> +     * The write must complete before the response timeout fired, 
>>> otherwise
>>> +     * the response is aborted and wait for next request
>>> +     * Return -EINVAL if the response is aborted
>>> +     */
>>> +    ret = (ssif_bmc->response_timer_inited) ? 0 : -EINVAL;
>>> +    if (ret)
>>> +        goto exit;
>>> +
>>> +    del_timer(&ssif_bmc->response_timer);
>>> +    ssif_bmc->response_timer_inited = false;
>>> +
>>> +    memcpy(&ssif_bmc->response, &msg, count);
>>> +    ssif_bmc->is_singlepart_read = (msg.len <= 
>>> MAX_PAYLOAD_PER_TRANSACTION);
>>> +
>>> +    ssif_bmc->response_in_progress = true;
>>> +
>>> +    /* ssif_bmc not busy */
>>> +    ssif_bmc->busy = false;
>>> +
>>> +    /* Clean old request buffer */
>>> +    memset(&ssif_bmc->request, 0, sizeof(struct ipmi_ssif_msg));
>>> +exit:
>>> +    spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>>> +
>>> +    return (ret < 0) ? ret : count;
>>> +}
>>> +
>>> +static int ssif_bmc_open(struct inode *inode, struct file *file)
>>> +{
>>> +    struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>>> +    int ret = 0;
>>> +
>>> +    spin_lock_irq(&ssif_bmc->lock);
>>> +    if (!ssif_bmc->running)
>>> +        ssif_bmc->running = 1;
>>> +    else
>>> +        ret = -EBUSY;
>>> +    spin_unlock_irq(&ssif_bmc->lock);
>>> +
>>> +    return ret;
>>> +}
>>> +
>>> +static __poll_t ssif_bmc_poll(struct file *file, poll_table *wait)
>>> +{
>>> +    struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>>> +    __poll_t mask = 0;
>>> +
>>> +    poll_wait(file, &ssif_bmc->wait_queue, wait);
>>> +
>>> +    spin_lock_irq(&ssif_bmc->lock);
>>> +    /* The request is available, userspace application can get the 
>>> request */
>>> +    if (ssif_bmc->request_available)
>>> +        mask |= POLLIN;
>>> +
>>> +    spin_unlock_irq(&ssif_bmc->lock);
>>> +
>>> +    return mask;
>>> +}
>>> +
>>> +static int ssif_bmc_release(struct inode *inode, struct file *file)
>>> +{
>>> +    struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>>> +
>>> +    spin_lock_irq(&ssif_bmc->lock);
>>> +    ssif_bmc->running = 0;
>>> +    spin_unlock_irq(&ssif_bmc->lock);
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +/*
>>> + * System calls to device interface for user apps
>>> + */
>>> +static const struct file_operations ssif_bmc_fops = {
>>> +    .owner        = THIS_MODULE,
>>> +    .open        = ssif_bmc_open,
>>> +    .read        = ssif_bmc_read,
>>> +    .write        = ssif_bmc_write,
>>> +    .release    = ssif_bmc_release,
>>> +    .poll        = ssif_bmc_poll,
>>> +};
>>> +
>>> +/* Called with ssif_bmc->lock held. */
>>> +static void complete_response(struct ssif_bmc_ctx *ssif_bmc)
>>> +{
>>> +    /* Invalidate response in buffer to denote it having been sent. */
>>> +    ssif_bmc->response.len = 0;
>>> +    ssif_bmc->response_in_progress = false;
>>> +    ssif_bmc->nbytes_processed = 0;
>>> +    ssif_bmc->remain_len = 0;
>>> +    ssif_bmc->busy = false;
>>> +    memset(&ssif_bmc->part_buf, 0, sizeof(struct ssif_part_buffer));
>>> +    wake_up_all(&ssif_bmc->wait_queue);
>>> +}
>>> +
>>> +static void response_timeout(struct timer_list *t)
>>> +{
>>> +    struct ssif_bmc_ctx *ssif_bmc = from_timer(ssif_bmc, t, 
>>> response_timer);
>>> +    unsigned long flags;
>>> +
>>> +    spin_lock_irqsave(&ssif_bmc->lock, flags);
>>> +
>>> +    /* Do nothing if the response is in progress */
>>> +    if (!ssif_bmc->response_in_progress) {
>>> +        /* Recover ssif_bmc from busy */
>>> +        ssif_bmc->busy = false;
>>> +        ssif_bmc->response_timer_inited = false;
>>> +        /* Set aborting flag */
>>> +        ssif_bmc->aborting = true;
>>> +    }
>>> +
>>> +    spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>>> +}
>>> +
>>> +/* Called with ssif_bmc->lock held. */
>>> +static void handle_request(struct ssif_bmc_ctx *ssif_bmc)
>>> +{
>>> +    /* set ssif_bmc to busy waiting for response */
>>> +    ssif_bmc->busy = true;
>>> +    /* Request message is available to process */
>>> +    ssif_bmc->request_available = true;
>>> +    /* Clean old response buffer */
>>> +    memset(&ssif_bmc->response, 0, sizeof(struct ipmi_ssif_msg));
>>> +    /* This is the new READ request.*/
>>> +    wake_up_all(&ssif_bmc->wait_queue);
>>> +
>>> +    /* Armed timer to recover slave from busy state in case of no 
>>> response */
>>> +    if (!ssif_bmc->response_timer_inited) {
>>> +        timer_setup(&ssif_bmc->response_timer, response_timeout, 0);
>>> +        ssif_bmc->response_timer_inited = true;
>>> +    }
>>> +    mod_timer(&ssif_bmc->response_timer, jiffies + 
>>> msecs_to_jiffies(RESPONSE_TIMEOUT));
>>> +}
>>> +
>>> +static void calculate_response_part_pec(struct ssif_part_buffer *part)
>>> +{
>>> +    u8 addr = part->address;
>>> +
>>> +    /* PEC - Start Read Address */
>>> +    part->pec = i2c_smbus_pec(0, &addr, 1);
>>> +    /* PEC - SSIF Command */
>>> +    part->pec = i2c_smbus_pec(part->pec, &part->smbus_cmd, 1);
>>> +    /* PEC - Restart Write Address */
>>> +    addr = addr | 0x01;
>>> +    part->pec = i2c_smbus_pec(part->pec, &addr, 1);
>>> +    part->pec = i2c_smbus_pec(part->pec, &part->length, 1);
>>> +    if (part->length)
>>> +        part->pec = i2c_smbus_pec(part->pec, part->payload, 
>>> part->length);
>>> +}
>>> +
>>> +static void set_singlepart_response_buffer(struct ssif_bmc_ctx 
>>> *ssif_bmc)
>>> +{
>>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>>> +
>>> +    part->address = GET_8BIT_ADDR(ssif_bmc->client->addr);
>>> +    part->length = (u8)ssif_bmc->response.len;
>>> +
>>> +    /* Clear the rest to 0 */
>>> +    memset(part->payload + part->length, 0, 
>>> MAX_PAYLOAD_PER_TRANSACTION - part->length);
>>> +    memcpy(&part->payload[0], &ssif_bmc->response.payload[0], 
>>> part->length);
>>> +}
>>> +
>>> +static void set_multipart_response_buffer(struct ssif_bmc_ctx 
>>> *ssif_bmc)
>>> +{
>>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>>> +    u8 part_len = 0;
>>> +
>>> +    part->address = GET_8BIT_ADDR(ssif_bmc->client->addr);
>>> +    switch (part->smbus_cmd) {
>>> +    case SSIF_IPMI_MULTIPART_READ_START:
>>> +        /*
>>> +         * Read Start length is 32 bytes.
>>> +         * Read Start transfer first 30 bytes of IPMI response
>>> +         * and 2 special code 0x00, 0x01.
>>> +         */
>>> +        ssif_bmc->nbytes_processed = 0;
>>> +        ssif_bmc->block_num = 0;
>>> +        part->length = MAX_PAYLOAD_PER_TRANSACTION;
>>> +        part_len = MAX_IPMI_DATA_PER_START_TRANSACTION;
>>> +        ssif_bmc->remain_len = ssif_bmc->response.len - part_len;
>>> +
>>> +        part->payload[0] = 0x00; /* Start Flag */
>>> +        part->payload[1] = 0x01; /* Start Flag */
>>> +
>>> +        memcpy(&part->payload[2], &ssif_bmc->response.payload[0], 
>>> part_len);
>>> +        break;
>>> +
>>> +    case SSIF_IPMI_MULTIPART_READ_MIDDLE:
>>> +        /*
>>> +         * IPMI READ Middle or READ End messages can carry up to 31 
>>> bytes
>>> +         * IPMI data plus block number byte.
>>> +         */
>>> +        if (ssif_bmc->remain_len <= 
>>> MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION) {
>>> +            /*
>>> +             * This is READ End message
>>> +             *  Return length is the remaining response data length
>>> +             *  plus block number
>>> +             *  Block number 0xFF is to indicate this is last message
>>> +             *
>>> +             */
>>> +            /* Clean the buffer */
>>> +            memset(&part->payload[0], 0, MAX_PAYLOAD_PER_TRANSACTION);
>>> +            part->length = ssif_bmc->remain_len + 1;
>>> +            part_len = ssif_bmc->remain_len;
>>> +            ssif_bmc->block_num = 0xFF;
>>> +            part->payload[0] = ssif_bmc->block_num;
>>> +        } else {
>>> +            /*
>>> +             * This is READ Middle message
>>> +             *  Response length is the maximum SMBUS transfer length
>>> +             *  Block number byte is incremented
>>> +             * Return length is maximum SMBUS transfer length
>>> +             */
>>> +            part->length = MAX_PAYLOAD_PER_TRANSACTION;
>>> +            part_len = MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
>>> +            part->payload[0] = ssif_bmc->block_num;
>>> +            ssif_bmc->block_num++;
>>> +        }
>>> +
>>> +        ssif_bmc->remain_len -= part_len;
>>> +        memcpy(&part->payload[1], ssif_bmc->response.payload + 
>>> ssif_bmc->nbytes_processed,
>>> +               part_len);
>>> +        break;
>>> +
>>> +    default:
>>> +        /* Do not expect to go to this case */
>>> +        dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus 
>>> command 0x%x\n",
>>> +            __func__, part->smbus_cmd);
>>> +        break;
>>> +    }
>>> +
>>> +    ssif_bmc->nbytes_processed += part_len;
>>> +}
>>> +
>>> +static bool supported_read_cmd(u8 cmd)
>>> +{
>>> +    if (cmd == SSIF_IPMI_SINGLEPART_READ ||
>>> +        cmd == SSIF_IPMI_MULTIPART_READ_START ||
>>> +        cmd == SSIF_IPMI_MULTIPART_READ_MIDDLE)
>>> +        return true;
>>> +
>>> +    return false;
>>> +}
>>> +
>>> +static bool supported_write_cmd(u8 cmd)
>>> +{
>>> +    if (cmd == SSIF_IPMI_SINGLEPART_WRITE ||
>>> +        cmd == SSIF_IPMI_MULTIPART_WRITE_START ||
>>> +        cmd == SSIF_IPMI_MULTIPART_WRITE_MIDDLE ||
>>> +        cmd == SSIF_IPMI_MULTIPART_WRITE_END)
>>> +        return true;
>>> +
>>> +    return false;
>>> +}
>>> +
>>> +/* Process the IPMI response that will be read by master */
>>> +static void handle_read_processed(struct ssif_bmc_ctx *ssif_bmc, u8 
>>> *val)
>>> +{
>>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>>> +
>>> +    /* msg_idx start from 0 */
>>> +    if (part->index < part->length)
>>> +        *val = part->payload[part->index];
>>> +    else if (part->index == part->length && ssif_bmc->pec_support)
>>> +        *val = part->pec;
>>> +    else
>>> +        *val = 0;
>>> +
>>> +    part->index++;
>>> +}
>>> +
>>> +static void handle_write_received(struct ssif_bmc_ctx *ssif_bmc, u8 
>>> *val)
>>> +{
>>> +    /*
>>> +     * The msg_idx must be 1 when first enter SSIF_REQ_RECVING state
>>> +     * And it would never exceeded 36 bytes included the 32 bytes 
>>> max payload +
>>> +     * the address + the command + the len and the PEC.
>>> +     */
>>> +    if (ssif_bmc->msg_idx < 1  || ssif_bmc->msg_idx > MAX_TRANSACTION)
>>> +        return;
>>> +
>>> +    if (ssif_bmc->msg_idx == 1) {
>>> +        ssif_bmc->part_buf.length = *val;
>>> +        ssif_bmc->part_buf.index = 0;
>>> +    } else {
>>> + ssif_bmc->part_buf.payload[ssif_bmc->part_buf.index++] = *val;
>>> +    }
>>> +
>>> +    ssif_bmc->msg_idx++;
>>> +}
>>> +
>>> +static bool validate_request_part(struct ssif_bmc_ctx *ssif_bmc)
>>> +{
>>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>>> +    bool ret = true;
>>> +    u8 cpec;
>>> +    u8 addr;
>>> +
>>> +    if (part->index == part->length) {
>>> +        /* PEC is not included */
>>> +        ssif_bmc->pec_support = false;
>>> +        ret = true;
>>> +        goto exit;
>>> +    }
>>> +
>>> +    if (part->index != part->length + 1) {
>>> +        ret = false;
>>> +        goto exit;
>>> +    }
>>> +
>>> +    /* PEC is included */
>>> +    ssif_bmc->pec_support = true;
>>> +    part->pec = part->payload[part->length];
>>> +    addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
>>> +    cpec = i2c_smbus_pec(0, &addr, 1);
>>> +    cpec = i2c_smbus_pec(cpec, &part->smbus_cmd, 1);
>>> +    cpec = i2c_smbus_pec(cpec, &part->length, 1);
>>> +    /*
>>> +     * As SMBus specification does not allow the length
>>> +     * (byte count) in the Write-Block protocol to be zero.
>>> +     * Therefore, it is illegal to have the last Middle
>>> +     * transaction in the sequence carry 32-byte and have
>>> +     * a length of ‘0’ in the End transaction.
>>> +     * But some users may try to use this way and we should
>>> +     * prevent ssif_bmc driver broken in this case.
>>> +     */
>>> +    if (part->length)
>>> +        cpec = i2c_smbus_pec(cpec, part->payload, part->length);
>>> +
>>> +    if (cpec != part->pec)
>>> +        ret = false;
>>> +
>>> +exit:
>>> +    return ret;
>>> +}
>>> +
>>> +static void process_request_part(struct ssif_bmc_ctx *ssif_bmc)
>>> +{
>>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>>> +    unsigned int len;
>>> +
>>> +    switch (part->smbus_cmd) {
>>> +    case SSIF_IPMI_SINGLEPART_WRITE:
>>> +        /* save the whole part to request*/
>>> +        ssif_bmc->request.len = part->length;
>>> +        memcpy(ssif_bmc->request.payload, part->payload, 
>>> part->length);
>>> +
>>> +        break;
>>> +    case SSIF_IPMI_MULTIPART_WRITE_START:
>>> +        ssif_bmc->request.len = 0;
>>> +
>>> +        fallthrough;
>>> +    case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
>>> +    case SSIF_IPMI_MULTIPART_WRITE_END:
>>> +        len = ssif_bmc->request.len + part->length;
>>> +        /* Do the bound check here, not allow the request len 
>>> exceed 254 bytes */
>>> +        if (len > IPMI_SSIF_PAYLOAD_MAX) {
>>> +            dev_warn(&ssif_bmc->client->dev,
>>> +                 "Warn: Request exceeded 254 bytes, aborting");
>>> +            /* Request too long, aborting */
>>> +            ssif_bmc->aborting =  true;
>>> +        } else {
>>> +            memcpy(ssif_bmc->request.payload + ssif_bmc->request.len,
>>> +                   part->payload, part->length);
>>> +            ssif_bmc->request.len += part->length;
>>> +        }
>>> +        break;
>>> +    default:
>>> +        /* Do not expect to go to this case */
>>> +        dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus 
>>> command 0x%x\n",
>>> +            __func__, part->smbus_cmd);
>>> +        break;
>>> +    }
>>> +}
>>> +
>>> +static void process_smbus_cmd(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>>> +{
>>> +    /* SMBUS command can vary (single or multi-part) */
>>> +    ssif_bmc->part_buf.smbus_cmd = *val;
>>> +    ssif_bmc->msg_idx = 1;
>>> +    memset(&ssif_bmc->part_buf.payload[0], 0, 
>>> MAX_PAYLOAD_PER_TRANSACTION);
>>> +
>>> +    if (*val == SSIF_IPMI_SINGLEPART_WRITE || *val == 
>>> SSIF_IPMI_MULTIPART_WRITE_START) {
>>> +        /*
>>> +         * The response maybe not come in-time, causing host SSIF 
>>> driver
>>> +         * to timeout and resend a new request. In such case check for
>>> +         * pending response and clear it
>>> +         */
>>> +        if (ssif_bmc->response_in_progress)
>>> +            complete_response(ssif_bmc);
>>> +
>>> +        /* This is new request, flip aborting flag if set */
>>> +        if (ssif_bmc->aborting)
>>> +            ssif_bmc->aborting = false;
>>> +    }
>>> +}
>>> +
>>> +static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, 
>>> u8 *val)
>>> +{
>>> +    if (ssif_bmc->state == SSIF_READY ||
>> Is this actually correct? The state machine seems to set this as the 
>> default state and in my testing we seem to always reach here with the 
>> state == SSIF_READY?
>
> The I2C_SLAVE_READ_REQUESTED event is expected to come on 
> SSIF_SMBUS_CMD state where Slave has already received and validated 
> the SMBus command, in this case is the I2C_SLAVE_READ_REQUESTED event 
> if the SMBus command indeed is the READ command. You can see the check 
> supported_read_cmd() below.
>
> If Slave see the I2C_SLAVE_READ_REQUESTED event on other states, it 
> will transition to SSIF_ABORTING state that discard everything until 
> there is a new transaction come.
>
> On READ, the sequence of Slave event should be as below:
> I2C_SLAVE_WRITE_REQUESTED (addr) => I2C_SLAVE_WRITE_RECEIVED (SMBus 
> cmd) => I2C_SLAVE_READ_REQUESTED (Slave feed the first byte) => 
> I2C_SLAVE_READ_PROCESSED (Slave 2nd byte) => .... => I2C_SLAVE_STOP
>
>>> +        ssif_bmc->state == SSIF_START ||
>>> +        ssif_bmc->state == SSIF_REQ_RECVING ||
>>> +        ssif_bmc->state == SSIF_RES_SENDING) {
>>> +        dev_warn(&ssif_bmc->client->dev,
>>> +             "Warn: %s unexpected READ REQUESTED in state=%s\n",
>>> +             __func__, state_to_string(ssif_bmc->state));
>>> +        ssif_bmc->state = SSIF_ABORTING;
>>> +        *val = 0;
>>> +        return;
>>> +
>>> +    } else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
>>> +        if (!supported_read_cmd(ssif_bmc->part_buf.smbus_cmd)) {
>>> +            dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus 
>>> read command=0x%x",
>>> +                 ssif_bmc->part_buf.smbus_cmd);
>>> +            ssif_bmc->aborting = true;
>>> +        }
>>> +
>>> +        if (ssif_bmc->aborting)
>>> +            ssif_bmc->state = SSIF_ABORTING;
>>> +        else
>>> +            ssif_bmc->state = SSIF_RES_SENDING;
>>> +    }
>>> +
>>> +    ssif_bmc->msg_idx = 0;
>>> +
>>> +    /* Send 0 if there is nothing to send */
>>> +    if (!ssif_bmc->response_in_progress || ssif_bmc->state == 
>>> SSIF_ABORTING) {
>>> +        *val = 0;
>>> +        return;
>>> +    }
>>> +
>>> +    if (ssif_bmc->is_singlepart_read)
>>> +        set_singlepart_response_buffer(ssif_bmc);
>>> +    else
>>> +        set_multipart_response_buffer(ssif_bmc);
>>> +
>>> +    calculate_response_part_pec(&ssif_bmc->part_buf);
>>> +    ssif_bmc->part_buf.index = 0;
>>> +    *val = ssif_bmc->part_buf.length;
>>> +}
>>> +
>>> +static void on_read_processed_event(struct ssif_bmc_ctx *ssif_bmc, 
>>> u8 *val)
>>> +{
>>> +    if (ssif_bmc->state == SSIF_READY ||
>> Same comment as above?
>
> Same here, I2C_SLAVE_READ_PROCESSED is expected to come after the 
> I2C_SLAVE_READ_REQUESTED or other I2C_SLAVE_READ_PROCESSED. ie: when 
> the state is SSIF_RES_SENDING.
> If it comes when Slave in states other than SSIF_RES_SENDING, the 
> Slave will transition to SSIF_ABORTING state.
>
>>> +        ssif_bmc->state == SSIF_START ||
>>> +        ssif_bmc->state == SSIF_REQ_RECVING ||
>>> +        ssif_bmc->state == SSIF_SMBUS_CMD) {
>>> +        dev_warn(&ssif_bmc->client->dev,
>>> +             "Warn: %s unexpected READ PROCESSED in state=%s\n",
>>> +             __func__, state_to_string(ssif_bmc->state));
>>> +        ssif_bmc->state = SSIF_ABORTING;
>>> +        *val = 0;
>>> +        return;
>>> +    }
>>> +
>>> +    /* Send 0 if there is nothing to send */
>>> +    if (!ssif_bmc->response_in_progress || ssif_bmc->state == 
>>> SSIF_ABORTING) {
>>> +        *val = 0;
>>> +        return;
>>> +    }
>>> +
>>> +    handle_read_processed(ssif_bmc, val);
>>> +}
>>> +
>>> +static void on_write_requested_event(struct ssif_bmc_ctx *ssif_bmc, 
>>> u8 *val)
>>> +{
>>> +    if (ssif_bmc->state == SSIF_READY || ssif_bmc->state == 
>>> SSIF_SMBUS_CMD) {
>>> +        ssif_bmc->state = SSIF_START;
>>> +
>>> +    } else if (ssif_bmc->state == SSIF_START ||
>>> +           ssif_bmc->state == SSIF_REQ_RECVING ||
>>> +           ssif_bmc->state == SSIF_RES_SENDING) {
>>> +        dev_warn(&ssif_bmc->client->dev,
>>> +             "Warn: %s unexpected WRITE REQUEST in state=%s\n",
>>> +             __func__, state_to_string(ssif_bmc->state));
>>> +        ssif_bmc->state = SSIF_ABORTING;
>>> +        return;
>>> +    }
>>> +
>>> +    ssif_bmc->msg_idx = 0;
>>> +    ssif_bmc->part_buf.address = *val;
>>> +}
>>> +
>>> +static void on_write_received_event(struct ssif_bmc_ctx *ssif_bmc, 
>>> u8 *val)
>>> +{
>>> +    if (ssif_bmc->state == SSIF_READY ||
>>> +        ssif_bmc->state == SSIF_RES_SENDING) {
>>> +        dev_warn(&ssif_bmc->client->dev,
>>> +             "Warn: %s unexpected WRITE RECEIVED in state=%s\n",
>>> +             __func__, state_to_string(ssif_bmc->state));
>>> +        ssif_bmc->state = SSIF_ABORTING;
>>> +
>>> +    } else if (ssif_bmc->state == SSIF_START) {
>>> +        ssif_bmc->state = SSIF_SMBUS_CMD;
>>> +
>>> +    } else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
>>> +        if (!supported_write_cmd(ssif_bmc->part_buf.smbus_cmd)) {
>>> +            dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus 
>>> write command=0x%x",
>>> +                 ssif_bmc->part_buf.smbus_cmd);
>>> +            ssif_bmc->aborting = true;
>>> +        }
>>> +
>>> +        if (ssif_bmc->aborting)
>>> +            ssif_bmc->state = SSIF_ABORTING;
>>> +        else
>>> +            ssif_bmc->state = SSIF_REQ_RECVING;
>>> +    }
>>> +
>>> +    /* This is response sending state */
>>> +    if (ssif_bmc->state == SSIF_REQ_RECVING)
>>> +        handle_write_received(ssif_bmc, val);
>>> +    else if (ssif_bmc->state == SSIF_SMBUS_CMD)
>>> +        process_smbus_cmd(ssif_bmc, val);
>>> +}
>>> +
>>> +static void on_stop_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>>> +{
>>> +    if (ssif_bmc->state == SSIF_READY ||
>>> +        ssif_bmc->state == SSIF_START ||
>>> +        ssif_bmc->state == SSIF_SMBUS_CMD ||
>>> +        ssif_bmc->state == SSIF_ABORTING) {
>>> +        dev_warn(&ssif_bmc->client->dev,
>>> +             "Warn: %s unexpected SLAVE STOP in state=%s\n",
>>> +             __func__, state_to_string(ssif_bmc->state));
>>> +        ssif_bmc->state = SSIF_READY;
>>> +
>>> +    } else if (ssif_bmc->state == SSIF_REQ_RECVING) {
>>> +        if (validate_request_part(ssif_bmc)) {
>>> +            process_request_part(ssif_bmc);
>>> +            if (ssif_bmc->part_buf.smbus_cmd == 
>>> SSIF_IPMI_SINGLEPART_WRITE ||
>>> +                ssif_bmc->part_buf.smbus_cmd == 
>>> SSIF_IPMI_MULTIPART_WRITE_END)
>>> +                handle_request(ssif_bmc);
>>> +            ssif_bmc->state = SSIF_READY;
>>> +        } else {
>>> +            /*
>>> +             * A BMC that receives an invalid request drop the data 
>>> for the write
>>> +             * transaction and any further transactions (read or 
>>> write) until
>>> +             * the next valid read or write Start transaction is 
>>> received
>>> +             */
>>> +            dev_err(&ssif_bmc->client->dev, "Error: invalid pec\n");
>>> +            ssif_bmc->aborting = true;
>>> +        }
>>> +    } else if (ssif_bmc->state == SSIF_RES_SENDING) {
>>> +        if (ssif_bmc->is_singlepart_read || ssif_bmc->block_num == 
>>> 0xFF)
>>> +            /* Invalidate response buffer to denote it is sent */
>>> +            complete_response(ssif_bmc);
>>> +        ssif_bmc->state = SSIF_READY;
>>> +    }
>>> +
>>> +    /* Reset message index */
>>> +    ssif_bmc->msg_idx = 0;
>>> +}
>>> +
>>> +/*
>>> + * Callback function to handle I2C slave events
>>> + */
>>> +static int ssif_bmc_cb(struct i2c_client *client, enum 
>>> i2c_slave_event event, u8 *val)
>>> +{
>>> +    unsigned long flags;
>>> +    struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
>>> +    int ret = 0;
>>> +
>>> +    spin_lock_irqsave(&ssif_bmc->lock, flags);
>>> +
>>> +    switch (event) {
>>> +    case I2C_SLAVE_READ_REQUESTED:
>>> +        on_read_requested_event(ssif_bmc, val);
>>> +        break;
>>> +
>>> +    case :
>>> +        on_write_requested_event(ssif_bmc, val);
>>> +        break;
>>> +
>>> +    case I2C_SLAVE_READ_PROCESSED:
>>> +        on_read_processed_event(ssif_bmc, val);
>>> +        break;
>>> +
>>> +    case I2C_SLAVE_WRITE_RECEIVED:
>>> +        on_write_received_event(ssif_bmc, val);
>>> +        break;
>>> +
>>> +    case I2C_SLAVE_STOP:
>>> +        on_stop_event(ssif_bmc, val);
>>> +        break;
>>> +
>>> +    default:
>>> +        dev_warn(&ssif_bmc->client->dev, "Warn: Unknown i2c slave 
>>> event\n");
>>> +        break;
>>> +    }
>>> +
>>> +    if (!ssif_bmc->aborting && ssif_bmc->busy)
>>> +        ret = -EBUSY;
>>> +
>>> +    spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>>> +
>>> +    return ret;
>>> +}
>>> +
>>> +static int ssif_bmc_probe(struct i2c_client *client, const struct 
>>> i2c_device_id *id)
>>> +{
>>> +    struct ssif_bmc_ctx *ssif_bmc;
>>> +    int ret;
>>> +
>>> +    ssif_bmc = devm_kzalloc(&client->dev, sizeof(*ssif_bmc), 
>>> GFP_KERNEL);
>>> +    if (!ssif_bmc)
>>> +        return -ENOMEM;
>>> +
>>> +    spin_lock_init(&ssif_bmc->lock);
>>> +
>>> +    init_waitqueue_head(&ssif_bmc->wait_queue);
>>> +    ssif_bmc->request_available = false;
>>> +    ssif_bmc->response_in_progress = false;
>>> +    ssif_bmc->busy = false;
>>> +    ssif_bmc->response_timer_inited = false;
>>> +
>>> +    /* Register misc device interface */
>>> +    ssif_bmc->miscdev.minor = MISC_DYNAMIC_MINOR;
>>> +    ssif_bmc->miscdev.name = DEVICE_NAME;
>>> +    ssif_bmc->miscdev.fops = &ssif_bmc_fops;
>>> +    ssif_bmc->miscdev.parent = &client->dev;
>>> +    ret = misc_register(&ssif_bmc->miscdev);
>>> +    if (ret)
>>> +        return ret;
>>> +
>>> +    ssif_bmc->client = client;
>>> +    ssif_bmc->client->flags |= I2C_CLIENT_SLAVE;
>>> +
>>> +    /* Register I2C slave */
>>> +    i2c_set_clientdata(client, ssif_bmc);
>>> +    ret = i2c_slave_register(client, ssif_bmc_cb);
>>> +    if (ret)
>>> +        misc_deregister(&ssif_bmc->miscdev);
>>> +
>>> +    return ret;
>>> +}
>>> +
>>> +static void ssif_bmc_remove(struct i2c_client *client)
>>> +{
>>> +    struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
>>> +
>>> +    i2c_slave_unregister(client);
>>> +    misc_deregister(&ssif_bmc->miscdev);
>>> +}
>>> +
>>> +static const struct of_device_id ssif_bmc_match[] = {
>>> +    { .compatible = "ssif-bmc" },
>>> +    { },
>>> +};
>>> +MODULE_DEVICE_TABLE(of, ssif_bmc_match);
>>> +
>>> +static const struct i2c_device_id ssif_bmc_id[] = {
>>> +    { DEVICE_NAME, 0 },
>>> +    { },
>>> +};
>>> +MODULE_DEVICE_TABLE(i2c, ssif_bmc_id);
>>> +
>>> +static struct i2c_driver ssif_bmc_driver = {
>>> +    .driver         = {
>>> +        .name           = DEVICE_NAME,
>>> +        .of_match_table = ssif_bmc_match,
>>> +    },
>>> +    .probe          = ssif_bmc_probe,
>>> +    .remove         = ssif_bmc_remove,
>>> +    .id_table       = ssif_bmc_id,
>>> +};
>>> +
>>> +module_i2c_driver(ssif_bmc_driver);
>>> +
>>> +MODULE_AUTHOR("Quan Nguyen <quan@os.amperecomputing.com>");
>>> +MODULE_AUTHOR("Chuong Tran <chuong@os.amperecomputing.com>");
>>> +MODULE_DESCRIPTION("Linux device driver of the BMC IPMI SSIF 
>>> interface.");
>>> +MODULE_LICENSE("GPL");
>>> diff --git a/include/uapi/linux/ipmi_ssif_bmc.h 
>>> b/include/uapi/linux/ipmi_ssif_bmc.h
>>> new file mode 100644
>>> index 000000000000..1c6a753dad08
>>> --- /dev/null
>>> +++ b/include/uapi/linux/ipmi_ssif_bmc.h
>>> @@ -0,0 +1,18 @@
>>> +/* SPDX-License-Identifier: GPL-2.0-only WITH Linux-syscall-note*/
>>> +/*
>>> + * Copyright (c) 2022, Ampere Computing LLC.
>>> + */
>>> +
>>> +#ifndef _UAPI_LINUX_IPMI_SSIF_BMC_H
>>> +#define _UAPI_LINUX_IPMI_SSIF_BMC_H
>>> +
>>> +#include <linux/types.h>
>>> +
>>> +/* Max length of ipmi ssif message included netfn and cmd field */
>>> +#define IPMI_SSIF_PAYLOAD_MAX         254
>>> +struct ipmi_ssif_msg {
>>> +    unsigned int len;
>>> +    __u8    payload[IPMI_SSIF_PAYLOAD_MAX];
>>> +};
>>> +
>>> +#endif /* _UAPI_LINUX_IPMI_SSIF_BMC_H */

On Mon, Oct 10, 2022 at 12:08:24PM +0100, Graeme Gregory wrote:
> 
> On 10/10/2022 02:28, Quan Nguyen wrote:
> > 
> > 
> > On 07/10/2022 20:26, Graeme Gregory wrote:
> > >
> > > On 04/10/2022 10:31, Quan Nguyen wrote:
> > > > The SMBus system interface (SSIF) IPMI BMC driver can be used to
> > > > perform
> > > > in-band IPMI communication with their host in management (BMC) side.
> > > >
> > > > Thanks Dan for the copy_from_user() fix in the link below.
> > > >
> > > > Link: https://lore.kernel.org/linux-arm-kernel/20220310114119.13736-4-quan@os.amperecomputing.com/
> > > > Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
> > >
> > > I have been testing this on our hardware and I don't seem to be able
> > > to get this driver working. I was using an older version.
> > >
> > > I have hacked ssifbridged to deal with the change in len from u8 to
> > > unsigned int.
> > >
> > > It works as long as I only ever send SSIF commands, any attempt to
> > > read a response crashes the state machine and the driver never
> > > recovers. No further SSIF comms is possible! (slave doesnt even ACK
> > > writes).
> > >
> > > A couple of comments below on possible state machine errors.
> > >
> > > Its possible I am doing something wrong!
> > >
> >
> > Thanks Graeme for the test and the comments.
> >
> > What's your testing hardware?
> >
> > This was tested with Aspeed ast2500 and ast2600 with the patch series
> > [1] below applied.
> >
> > If you use the same hw, could you pick the series and see if any thing
> > improve ?
> >
> > [1] https://lore.kernel.org/all/20210616031046.2317-1-quan@os.amperecomputing.com/
> >
> Thanks, that patch series does stop the state machine crashing.
>
> I am testing on AST2600EVB with A1 rev, but we also have our own DC-SCM with
> A3 chip.
>
> Responses are still not working for me, but I think that may be an error in
> my ssifbridged hacks.
>
> Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c ssifbridged[335]: Read ssif
> request message with len=13 netfn=44 lun=0 cmd=2
>
> Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c ipmid[312]: BootCode:
> 000000000000000000
>
> Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c ssifbridged[335]: Send ssif
> respond message with len=4 netfn=45 lun=0 cmd=2 cc=0
>
> Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c kernel: ipmi-ssif-host 0-0010:
> Warn: on_read_requested_event unexpected READ REQUESTED in state=SSIF_READY
>
> Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c kernel: ipmi-ssif-host 0-0010:
> Warn: on_stop_event unexpected SLAVE STOP in state=SSIF_ABORTING
>
Just to close the loop on this, I have now fully tested this driver on
our setup internally.

Final hitch turned out to be an aardvark not issuing STOP events between
reads/writes.

Thanks for the work.

Graeme

On 14/10/2022 20:05, Graeme Gregory wrote:
> On Mon, Oct 10, 2022 at 12:08:24PM +0100, Graeme Gregory wrote:
>>
>> On 10/10/2022 02:28, Quan Nguyen wrote:
>>>
>>>
>>> On 07/10/2022 20:26, Graeme Gregory wrote:
>>>>
>>>> On 04/10/2022 10:31, Quan Nguyen wrote:
>>>>> The SMBus system interface (SSIF) IPMI BMC driver can be used to
>>>>> perform
>>>>> in-band IPMI communication with their host in management (BMC) side.
>>>>>
>>>>> Thanks Dan for the copy_from_user() fix in the link below.
>>>>>
>>>>> Link: https://lore.kernel.org/linux-arm-kernel/20220310114119.13736-4-quan@os.amperecomputing.com/
>>>>> Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
>>>>
>>>> I have been testing this on our hardware and I don't seem to be able
>>>> to get this driver working. I was using an older version.
>>>>
>>>> I have hacked ssifbridged to deal with the change in len from u8 to
>>>> unsigned int.
>>>>
>>>> It works as long as I only ever send SSIF commands, any attempt to
>>>> read a response crashes the state machine and the driver never
>>>> recovers. No further SSIF comms is possible! (slave doesnt even ACK
>>>> writes).
>>>>
>>>> A couple of comments below on possible state machine errors.
>>>>
>>>> Its possible I am doing something wrong!
>>>>
>>>
>>> Thanks Graeme for the test and the comments.
>>>
>>> What's your testing hardware?
>>>
>>> This was tested with Aspeed ast2500 and ast2600 with the patch series
>>> [1] below applied.
>>>
>>> If you use the same hw, could you pick the series and see if any thing
>>> improve ?
>>>
>>> [1] https://lore.kernel.org/all/20210616031046.2317-1-quan@os.amperecomputing.com/
>>>
>> Thanks, that patch series does stop the state machine crashing.
>>
>> I am testing on AST2600EVB with A1 rev, but we also have our own DC-SCM with
>> A3 chip.
>>
>> Responses are still not working for me, but I think that may be an error in
>> my ssifbridged hacks.
>>
>> Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c ssifbridged[335]: Read ssif
>> request message with len=13 netfn=44 lun=0 cmd=2
>>
>> Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c ipmid[312]: BootCode:
>> 000000000000000000
>>
>> Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c ssifbridged[335]: Send ssif
>> respond message with len=4 netfn=45 lun=0 cmd=2 cc=0
>>
>> Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c kernel: ipmi-ssif-host 0-0010:
>> Warn: on_read_requested_event unexpected READ REQUESTED in state=SSIF_READY
>>
>> Oct 10 10:54:55 qcom-evb-proto-ccf37d18ea0c kernel: ipmi-ssif-host 0-0010:
>> Warn: on_stop_event unexpected SLAVE STOP in state=SSIF_ABORTING
>>
> Just to close the loop on this, I have now fully tested this driver on
> our setup internally.
> 
> Final hitch turned out to be an aardvark not issuing STOP events between
> reads/writes.
> 
> Thanks for the work.
> 

Thanks a lot Graeme, for the test.

- Quan