[v4,01/11] can: Add LIN bus as CAN abstraction

Introduce a LIN (local interconnect network) abstraction on top of CAN.
This is a glue driver adapting CAN on one side while offering LIN
abstraction on the other side. So that upcoming LIN device drivers can
make use of it.

Tested-by: Andreas Lauser <andreas.lauser@mercedes-benz.com>
Signed-off-by: Christoph Fritz <christoph.fritz@hexdev.de>
---
 drivers/net/can/Kconfig          |  10 +
 drivers/net/can/Makefile         |   1 +
 drivers/net/can/lin.c            | 470 +++++++++++++++++++++++++++++++
 include/net/lin.h                |  90 ++++++
 include/uapi/linux/can/netlink.h |   1 +
 5 files changed, 572 insertions(+)
 create mode 100644 drivers/net/can/lin.c
 create mode 100644 include/net/lin.h

On Thu, 9 May 2024, Christoph Fritz wrote:

> Introduce a LIN (local interconnect network) abstraction on top of CAN.
> This is a glue driver adapting CAN on one side while offering LIN
> abstraction on the other side. So that upcoming LIN device drivers can
> make use of it.
> 
> Tested-by: Andreas Lauser <andreas.lauser@mercedes-benz.com>
> Signed-off-by: Christoph Fritz <christoph.fritz@hexdev.de>
> ---
>  drivers/net/can/Kconfig          |  10 +
>  drivers/net/can/Makefile         |   1 +
>  drivers/net/can/lin.c            | 470 +++++++++++++++++++++++++++++++
>  include/net/lin.h                |  90 ++++++
>  include/uapi/linux/can/netlink.h |   1 +
>  5 files changed, 572 insertions(+)
>  create mode 100644 drivers/net/can/lin.c
>  create mode 100644 include/net/lin.h
> 
> diff --git a/drivers/net/can/lin.c b/drivers/net/can/lin.c
> new file mode 100644
> index 0000000000000..a22768c17e3f8
> --- /dev/null
> +++ b/drivers/net/can/lin.c
> @@ -0,0 +1,470 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/* Copyright (C) 2024 hexDEV GmbH - https://hexdev.de */
> +
> +#include <linux/can/core.h>
> +#include <linux/can/dev.h>
> +#include <linux/can/error.h>
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/netdevice.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <net/lin.h>
> +
> +static const u8 lin_id_parity_tbl[] = {
> +	0x80, 0xC0, 0x40, 0x00, 0xC0, 0x80, 0x00, 0x40,
> +	0x00, 0x40, 0xC0, 0x80, 0x40, 0x00, 0x80, 0xC0,
> +	0x40, 0x00, 0x80, 0xC0, 0x00, 0x40, 0xC0, 0x80,
> +	0xC0, 0x80, 0x00, 0x40, 0x80, 0xC0, 0x40, 0x00,
> +	0x00, 0x40, 0xC0, 0x80, 0x40, 0x00, 0x80, 0xC0,
> +	0x80, 0xC0, 0x40, 0x00, 0xC0, 0x80, 0x00, 0x40,
> +	0xC0, 0x80, 0x00, 0x40, 0x80, 0xC0, 0x40, 0x00,
> +	0x40, 0x00, 0x80, 0xC0, 0x00, 0x40, 0xC0, 0x80,
> +};
> +
> +u8 lin_get_id_parity(u8 id)
> +{
> +	return lin_id_parity_tbl[id];
> +}
> +EXPORT_SYMBOL(lin_get_id_parity);
> +
> +static ssize_t lin_identifier_show(struct device *dev,
> +				   struct device_attribute *attr, char *buf)
> +{
> +	struct lin_device *ldev = netdev_priv(to_net_dev(dev));
> +	struct lin_responder_answer answ;
> +	int k, count, ret;
> +	long id;
> +
> +	if (!ldev->ldev_ops->get_responder_answer)
> +		return -EOPNOTSUPP;
> +
> +	ret = kstrtol(attr->attr.name, 16, &id);
> +	if (ret)
> +		return ret;
> +	if (id < 0 || id >= LIN_NUM_IDS)

How can this happen?

Perhaps you can determine the id arithmetically from a pointer within an 
array?

> +		return -EINVAL;
> +
> +	count = sysfs_emit(buf, "%-6s %-11s %-9s %-9s %-2s %-24s %-6s\n",
> +			   "state", "cksum-mode", "is_event", "event_id",
> +			   "n", "data", "cksum");
> +
> +	ret = ldev->ldev_ops->get_responder_answer(ldev, id, &answ);
> +	if (ret)
> +		return ret;
> +
> +	count += sysfs_emit_at(buf, count, "%-6s %-11s %-9s %-9u %-2u ",
> +			       answ.is_active ? "active" : "off",
> +			       answ.lf.checksum_mode ? "enhanced" : "classic",
> +			       answ.is_event_frame ? "yes" : "no",
> +			       answ.event_associated_id,
> +			       answ.lf.len);
> +
> +	for (k = 0; k < answ.lf.len; k++)
> +		count += sysfs_emit_at(buf, count, "%02x ", answ.lf.data[k]);
> +	for (; k < 8; k++)
> +		count += sysfs_emit_at(buf, count, "   ");
> +	if (answ.lf.len)
> +		count += sysfs_emit_at(buf, count, " %02x", answ.lf.checksum);
> +
> +	count += sysfs_emit_at(buf, count, "\n");
> +
> +	return count;
> +}
> +
> +static const char *parse_and_advance(const char *buf, long *result,
> +				     unsigned int base)
> +{
> +	char num_str[5] = {0};
> +	int num_len = 0;
> +
> +	while (*buf && isspace(*buf))

Missing #include for isspace().

> +		buf++;
> +	while (*buf && isalnum(*buf) && num_len < sizeof(num_str) - 1)
> +		num_str[num_len++] = *buf++;

This is likely broken when the number is too long because the next 
number is not correctly parsed? I think you should bail out with an error 
when a number is invalid (too long).

> +	if (kstrtol(num_str, base, result))

Missing #include for kstrtol() but see b.

Do you care for signed numbers? If not use unsigned kstrtox variant and 
typing.

> +		return NULL;
> +
> +	return buf;
> +}
> +
> +static ssize_t lin_identifier_store(struct device *dev,
> +				    struct device_attribute *attr,
> +				    const char *buf, size_t count)
> +{
> +	struct lin_device *ldev = netdev_priv(to_net_dev(dev));
> +	struct lin_responder_answer answ = { 0 };
> +	const char *ptr = buf;
> +	int ret;
> +	long v;
> +
> +	if (!ldev->ldev_ops->update_responder_answer)
> +		return -EOPNOTSUPP;
> +
> +	ret = kstrtol(attr->attr.name, 16, &v);
> +	if (ret)
> +		return ret;
> +	if (v < 0 || v >= LIN_NUM_IDS)
> +		return -EINVAL;

Can this happen?

> +	answ.lf.lin_id = v;
> +
> +	ptr = parse_and_advance(ptr, &v, 2);
> +	if (!ptr)
> +		return -EINVAL;
> +	answ.is_active = v != 0;
> +
> +	ptr = parse_and_advance(ptr, &v, 2);
> +	if (!ptr)
> +		return -EINVAL;
> +	answ.lf.checksum_mode = v != 0;
> +
> +	ptr = parse_and_advance(ptr, &v, 2);
> +	if (!ptr)
> +		return -EINVAL;
> +	answ.is_event_frame = v != 0;
> +
> +	ptr = parse_and_advance(ptr, &v, 16);
> +	if (!ptr || v > LIN_ID_MASK)
> +		return -EINVAL;
> +	answ.event_associated_id = v;
> +
> +	ptr = parse_and_advance(ptr, &v, 16);
> +	if (!ptr || v > LIN_MAX_DLEN)
> +		return -EINVAL;
> +	answ.lf.len = v;
> +
> +	for (int i = 0; i < answ.lf.len; i++) {
> +		ptr = parse_and_advance(ptr, &v, 16);
> +		if (!ptr)
> +			return -EINVAL;
> +		answ.lf.data[i] = v;
> +	}
> +	ret = ldev->ldev_ops->update_responder_answer(ldev, &answ);
> +	if (ret)
> +		return ret;
> +
> +	return count;
> +}

When adding sysfs entries, they should be documented under 
Documentation/ABI/

> +#define LID(_name) \
> +	struct device_attribute linid_##_name = __ATTR(_name, 0644, \
> +	lin_identifier_show, lin_identifier_store)
> +
> +LID(00); LID(01); LID(02); LID(03); LID(04); LID(05); LID(06); LID(07);
> +LID(08); LID(09); LID(0a); LID(0b); LID(0c); LID(0d); LID(0e); LID(0f);
> +LID(10); LID(11); LID(12); LID(13); LID(14); LID(15); LID(16); LID(17);
> +LID(18); LID(19); LID(1a); LID(1b); LID(1c); LID(1d); LID(1e); LID(1f);
> +LID(20); LID(21); LID(22); LID(23); LID(24); LID(25); LID(26); LID(27);
> +LID(28); LID(29); LID(2a); LID(2b); LID(2c); LID(2d); LID(2e); LID(2f);
> +LID(30); LID(31); LID(32); LID(33); LID(34); LID(35); LID(36); LID(37);
> +LID(38); LID(39); LID(3a); LID(3b); LID(3c); LID(3d); LID(3e); LID(3f);
> +
> +static struct attribute *lin_sysfs_attrs[] = {
> +	&linid_00.attr, &linid_01.attr, &linid_02.attr, &linid_03.attr,
> +	&linid_04.attr, &linid_05.attr, &linid_06.attr, &linid_07.attr,
> +	&linid_08.attr, &linid_09.attr, &linid_0a.attr, &linid_0b.attr,
> +	&linid_0c.attr, &linid_0d.attr, &linid_0e.attr, &linid_0f.attr,
> +	&linid_10.attr, &linid_11.attr, &linid_12.attr, &linid_13.attr,
> +	&linid_14.attr, &linid_15.attr, &linid_16.attr, &linid_17.attr,
> +	&linid_18.attr, &linid_19.attr, &linid_1a.attr, &linid_1b.attr,
> +	&linid_1c.attr, &linid_1d.attr, &linid_1e.attr, &linid_1f.attr,
> +	&linid_20.attr, &linid_21.attr, &linid_22.attr, &linid_23.attr,
> +	&linid_24.attr, &linid_25.attr, &linid_26.attr, &linid_27.attr,
> +	&linid_28.attr, &linid_29.attr, &linid_2a.attr, &linid_2b.attr,
> +	&linid_2c.attr, &linid_2d.attr, &linid_2e.attr, &linid_2f.attr,
> +	&linid_30.attr, &linid_31.attr, &linid_32.attr, &linid_33.attr,
> +	&linid_34.attr, &linid_35.attr, &linid_36.attr, &linid_37.attr,
> +	&linid_38.attr, &linid_39.attr, &linid_3a.attr, &linid_3b.attr,
> +	&linid_3c.attr, &linid_3d.attr, &linid_3e.attr, &linid_3f.attr,
> +	NULL
> +};
> +
> +static const struct attribute_group lin_sysfs_group = {
> +	.name = "lin_ids",
> +	.attrs = lin_sysfs_attrs,
> +};
> +
> +static void lin_tx_work_handler(struct work_struct *ws)
> +{
> +	struct lin_device *ldev = container_of(ws, struct lin_device,
> +					       tx_work);
> +	struct net_device *ndev = ldev->ndev;
> +	struct canfd_frame *cfd;
> +	struct lin_frame lf;
> +	int ret;
> +
> +	ldev->tx_busy = true;
> +
> +	cfd = (struct canfd_frame *)ldev->tx_skb->data;
> +	lf.checksum_mode = (cfd->can_id & LIN_ENHANCED_CKSUM_FLAG) ?
> +			   LINBUS_ENHANCED : LINBUS_CLASSIC;
> +	lf.lin_id = cfd->can_id & LIN_ID_MASK;
> +	lf.len = min(cfd->len, LIN_MAX_DLEN);

I wonder if it is the correct approach to continue in this case? Something 
is getting truncated here, right?

> +	memcpy(lf.data, cfd->data, lf.len);
> +
> +	ret = ldev->ldev_ops->ldo_tx(ldev, &lf);
> +	if (ret) {
> +		DEV_STATS_INC(ndev, tx_dropped);
> +		netdev_err_once(ndev, "transmission failure %d\n", ret);
> +		goto lin_tx_out;
> +	}
> +
> +	DEV_STATS_INC(ndev, tx_packets);
> +	DEV_STATS_ADD(ndev, tx_bytes, lf.len);
> +
> +lin_tx_out:
> +	ldev->tx_busy = false;
> +	netif_wake_queue(ndev);
> +}
> +
> +static netdev_tx_t lin_start_xmit(struct sk_buff *skb,
> +				  struct net_device *ndev)
> +{
> +	struct lin_device *ldev = netdev_priv(ndev);
> +
> +	if (ldev->tx_busy)

I'm skeptical this could be correct without any concurrency control 
related primitives.

> +		return NETDEV_TX_BUSY;
> +
> +	netif_stop_queue(ndev);
> +	ldev->tx_skb = skb;
> +	queue_work(ldev->wq, &ldev->tx_work);
> +
> +	return NETDEV_TX_OK;
> +}
> +
> +static int lin_open(struct net_device *ndev)
> +{
> +	struct lin_device *ldev = netdev_priv(ndev);
> +	int ret;
> +
> +	ldev->tx_busy = false;
> +
> +	ret = open_candev(ndev);
> +	if (ret)
> +		return ret;
> +
> +	netif_wake_queue(ndev);
> +
> +	ldev->can.state = CAN_STATE_ERROR_ACTIVE;
> +	ndev->mtu = CANFD_MTU;
> +
> +	return ldev->ldev_ops->ldo_open(ldev);
> +}
> +
> +static int lin_stop(struct net_device *ndev)
> +{
> +	struct lin_device *ldev = netdev_priv(ndev);
> +
> +	close_candev(ndev);
> +
> +	flush_work(&ldev->tx_work);
> +
> +	ldev->can.state = CAN_STATE_STOPPED;
> +
> +	return ldev->ldev_ops->ldo_stop(ldev);
> +}
> +
> +static const struct net_device_ops lin_netdev_ops = {
> +	.ndo_open = lin_open,
> +	.ndo_stop = lin_stop,
> +	.ndo_start_xmit = lin_start_xmit,
> +	.ndo_change_mtu = can_change_mtu,
> +};
> +
> +u8 lin_get_checksum(u8 pid, u8 n_of_bytes, const u8 *bytes,
> +		    enum lin_checksum_mode cm)
> +{
> +	unsigned int csum = 0;
> +	int i;

Use unsigned int for loop variables that are counting positive things.

> +	if (cm == LINBUS_ENHANCED)
> +		csum += pid;
> +
> +	for (i = 0; i < n_of_bytes; i++) {
> +		csum += bytes[i];
> +		if (csum > 255)
> +			csum -= 255;
> +	}
> +
> +	return (~csum & 0xff);

Unnecessary parenthesis.

> +}
> +EXPORT_SYMBOL_GPL(lin_get_checksum);
> +
> +static int lin_bump_rx_err(struct lin_device *ldev, const struct lin_frame *lf)
> +{
> +	struct net_device *ndev = ldev->ndev;
> +	struct can_frame cf = {0 };

Extra space.

I think ... = {} is enough if you want to just to fully initialize it.

> +
> +	if (lf->lin_id > LIN_ID_MASK) {
> +		netdev_dbg(ndev, "id exceeds LIN max id\n");
> +		cf.can_id = CAN_ERR_FLAG | CAN_ERR_PROT;
> +		cf.data[3] = CAN_ERR_PROT_LOC_ID12_05;
> +	}
> +
> +	if (lf->len > LIN_MAX_DLEN) {
> +		netdev_dbg(ndev, "frame exceeds number of bytes\n");
> +		cf.can_id = CAN_ERR_FLAG | CAN_ERR_PROT;
> +		cf.data[3] = CAN_ERR_PROT_LOC_DLC;
> +	}
> +
> +	if (lf->len) {
> +		u8 checksum = lin_get_checksum(LIN_FORM_PID(lf->lin_id),
> +					       lf->len, lf->data,
> +					       lf->checksum_mode);
> +
> +		if (checksum != lf->checksum) {
> +			netdev_dbg(ndev, "expected cksm: 0x%02x got: 0x%02x\n",
> +				   checksum, lf->checksum);
> +			cf.can_id = CAN_ERR_FLAG | CAN_ERR_PROT;
> +			cf.data[2] = CAN_ERR_PROT_FORM;
> +		}
> +	}
> +
> +	if (cf.can_id & CAN_ERR_FLAG) {
> +		struct can_frame *err_cf;
> +		struct sk_buff *skb = alloc_can_err_skb(ndev, &err_cf);
> +
> +		if (unlikely(!skb))
> +			return -ENOMEM;
> +
> +		err_cf->can_id |= cf.can_id;
> +		memcpy(err_cf->data, cf.data, CAN_MAX_DLEN);
> +
> +		netif_rx(skb);
> +
> +		return -EREMOTEIO;
> +	}
> +
> +	return 0;
> +}
> +
> +int lin_rx(struct lin_device *ldev, const struct lin_frame *lf)
> +{
> +	struct net_device *ndev = ldev->ndev;
> +	struct can_frame *cf;
> +	struct sk_buff *skb;
> +	int ret;
> +
> +	if (ldev->can.state == CAN_STATE_STOPPED)
> +		return 0;
> +
> +	netdev_dbg(ndev, "id:%02x, len:%u, data:%*ph, checksum:%02x (%s)\n",
> +		   lf->lin_id, lf->len, lf->len, lf->data, lf->checksum,
> +		   lf->checksum_mode ? "enhanced" : "classic");
> +
> +	ret = lin_bump_rx_err(ldev, lf);
> +	if (ret) {
> +		DEV_STATS_INC(ndev, rx_dropped);
> +		return ret;
> +	}
> +
> +	skb = alloc_can_skb(ndev, &cf);
> +	if (unlikely(!skb)) {
> +		DEV_STATS_INC(ndev, rx_dropped);
> +		return -ENOMEM;
> +	}
> +
> +	cf->can_id = lf->lin_id;
> +	cf->len = min(lf->len, LIN_MAX_DLEN);
> +	memcpy(cf->data, lf->data, cf->len);
> +
> +	DEV_STATS_INC(ndev, rx_packets);
> +	DEV_STATS_ADD(ndev, rx_bytes, cf->len);
> +
> +	netif_receive_skb(skb);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(lin_rx);
> +
> +static int lin_set_bittiming(struct net_device *ndev)
> +{
> +	struct lin_device *ldev = netdev_priv(ndev);
> +	unsigned int bitrate = ldev->can.bittiming.bitrate;
> +
> +	return ldev->ldev_ops->update_bitrate(ldev, bitrate);
> +}
> +
> +static const u32 lin_bitrate[] = { 1200, 2400, 4800, 9600, 19200 };
> +
> +struct lin_device *register_lin(struct device *dev,
> +				const struct lin_device_ops *ldops)
> +{
> +	struct net_device *ndev;
> +	struct lin_device *ldev;
> +	int ret;
> +
> +	if (!ldops || !ldops->ldo_tx || !ldops->update_bitrate  ||

Extra space.

> +	    !ldops->ldo_open || !ldops->ldo_stop) {
> +		dev_err(dev, "missing mandatory lin_device_ops\n");

Is this a programming error? WARN_ON_ONCE() around the condition would be 
warranted in that case.

> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	ndev = alloc_candev(sizeof(struct lin_device), 1);
> +	if (!ndev)
> +		return ERR_PTR(-ENOMEM);
> +
> +	ldev = netdev_priv(ndev);
> +
> +	ldev->ldev_ops = ldops;
> +	ndev->netdev_ops = &lin_netdev_ops;
> +	ndev->flags |= IFF_ECHO;
> +	ndev->mtu = CANFD_MTU;
> +	ndev->sysfs_groups[0] = &lin_sysfs_group;
> +	ldev->can.bittiming.bitrate = LIN_DEFAULT_BAUDRATE;
> +	ldev->can.ctrlmode = CAN_CTRLMODE_LIN;
> +	ldev->can.ctrlmode_supported = 0;
> +	ldev->can.bitrate_const = lin_bitrate;
> +	ldev->can.bitrate_const_cnt = ARRAY_SIZE(lin_bitrate);
> +	ldev->can.do_set_bittiming = lin_set_bittiming;
> +	ldev->ndev = ndev;
> +	ldev->dev = dev;
> +
> +	SET_NETDEV_DEV(ndev, dev);
> +
> +	ret = lin_set_bittiming(ndev);
> +	if (ret) {
> +		netdev_err(ndev, "set bittiming failed\n");
> +		goto exit_candev;
> +	}
> +
> +	ret = register_candev(ndev);
> +	if (ret)
> +		goto exit_candev;
> +
> +	/* Using workqueue as tx over USB/SPI/... may sleep */
> +	ldev->wq = alloc_workqueue(dev_name(dev), WQ_FREEZABLE | WQ_MEM_RECLAIM,
> +				   0);
> +	if (!ldev->wq) {
> +		ret = -ENOMEM;
> +		goto exit_unreg;
> +	}
> +
> +	INIT_WORK(&ldev->tx_work, lin_tx_work_handler);
> +
> +	netdev_info(ndev, "LIN initialized\n");
> +
> +	return ldev;
> +
> +exit_unreg:
> +	unregister_candev(ndev);
> +exit_candev:
> +	free_candev(ndev);
> +	return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL_GPL(register_lin);
> +
> +void unregister_lin(struct lin_device *ldev)
> +{
> +	struct net_device *ndev = ldev->ndev;
> +
> +	unregister_candev(ndev);
> +	destroy_workqueue(ldev->wq);

Why is the order different from that in register side?

> +	free_candev(ndev);
> +}
> +EXPORT_SYMBOL_GPL(unregister_lin);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Christoph Fritz <christoph.fritz@hexdev.de>");
> +MODULE_DESCRIPTION("LIN bus to CAN glue driver");
> diff --git a/include/net/lin.h b/include/net/lin.h
> new file mode 100644
> index 0000000000000..31bb0feefd188
> --- /dev/null
> +++ b/include/net/lin.h
> @@ -0,0 +1,90 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/* Copyright (C) 2024 hexDEV GmbH - https://hexdev.de */
> +
> +#ifndef _NET_LIN_H_
> +#define _NET_LIN_H_
> +
> +#include <linux/bitfield.h>
> +#include <linux/can/dev.h>
> +#include <linux/device.h>
> +
> +#define LIN_NUM_IDS		64
> +#define LIN_HEADER_SIZE		3
> +#define LIN_MAX_DLEN		8
> +
> +#define LIN_MAX_BAUDRATE	20000
> +#define LIN_MIN_BAUDRATE	1000
> +#define LIN_DEFAULT_BAUDRATE	9600
> +#define LIN_SYNC_BYTE		0x55
> +
> +#define LIN_ID_MASK		GENMASK(5, 0)
> +/* special ID descriptions for LIN */
> +#define LIN_RXOFFLOAD_DATA_FLAG	BIT(9)
> +#define LIN_ENHANCED_CKSUM_FLAG	BIT(8)
> +
> +extern u8 lin_get_id_parity(u8 id);
> +
> +#define LIN_GET_ID(PID)		FIELD_GET(LIN_ID_MASK, PID)
> +#define LIN_FORM_PID(ID)	(LIN_GET_ID(ID) | \
> +					lin_get_id_parity(LIN_GET_ID(ID)))
> +#define LIN_GET_PARITY(PID)	((PID) & ~LIN_ID_MASK)
> +#define LIN_CHECK_PID(PID)	(LIN_GET_PARITY(PID) == \
> +					LIN_GET_PARITY(LIN_FORM_PID(PID)))
> +
> +struct lin_attr {
> +	struct kobj_attribute attr;
> +	struct lin_device *ldev;
> +};
> +
> +struct lin_device {
> +	struct can_priv can;  /* must be the first member */
> +	struct net_device *ndev;
> +	struct device *dev;
> +	const struct lin_device_ops *ldev_ops;
> +	struct workqueue_struct *wq;
> +	struct work_struct tx_work;
> +	bool tx_busy;
> +	struct sk_buff *tx_skb;
> +};
> +
> +enum lin_checksum_mode {
> +	LINBUS_CLASSIC = 0,
> +	LINBUS_ENHANCED,
> +};
> +
> +struct lin_frame {
> +	u8 lin_id;
> +	u8 len;
> +	u8 data[LIN_MAX_DLEN];
> +	u8 checksum;
> +	enum lin_checksum_mode checksum_mode;
> +};
> +
> +struct lin_responder_answer {
> +	bool is_active;
> +	bool is_event_frame;
> +	u8 event_associated_id;
> +	struct lin_frame lf;
> +};
> +
> +struct lin_device_ops {
> +	int (*ldo_open)(struct lin_device *ldev);
> +	int (*ldo_stop)(struct lin_device *ldev);
> +	int (*ldo_tx)(struct lin_device *ldev, const struct lin_frame *frame);
> +	int (*update_bitrate)(struct lin_device *ldev, u16 bitrate);
> +	int (*update_responder_answer)(struct lin_device *ldev,
> +				       const struct lin_responder_answer *answ);
> +	int (*get_responder_answer)(struct lin_device *ldev, u8 id,
> +				    struct lin_responder_answer *answ);
> +};
> +
> +int lin_rx(struct lin_device *ldev, const struct lin_frame *lf);
> +
> +u8 lin_get_checksum(u8 pid, u8 n_of_bytes, const u8 *bytes,
> +		    enum lin_checksum_mode cm);
> +
> +struct lin_device *register_lin(struct device *dev,
> +				const struct lin_device_ops *ldops);
> +void unregister_lin(struct lin_device *ldev);
> +
> +#endif /* _NET_LIN_H_ */
> diff --git a/include/uapi/linux/can/netlink.h b/include/uapi/linux/can/netlink.h
> index 02ec32d694742..a37f56d86c5f2 100644
> --- a/include/uapi/linux/can/netlink.h
> +++ b/include/uapi/linux/can/netlink.h
> @@ -103,6 +103,7 @@ struct can_ctrlmode {
>  #define CAN_CTRLMODE_CC_LEN8_DLC	0x100	/* Classic CAN DLC option */
>  #define CAN_CTRLMODE_TDC_AUTO		0x200	/* CAN transiver automatically calculates TDCV */
>  #define CAN_CTRLMODE_TDC_MANUAL		0x400	/* TDCV is manually set up by user */
> +#define CAN_CTRLMODE_LIN		BIT(11)	/* LIN bus mode */
>  
>  /*
>   * CAN device statistics
>