| Message ID | 20220422040803.2524940-4-quan@os.amperecomputing.com |
|---|---|
| State | New |
| Headers | show |
| Series | Add SSIF BMC driver | expand |
On Fri, Apr 22, 2022 at 11:08:03AM +0700, Quan Nguyen wrote: > When processing I2C_SLAVE_WRITE_REQUESTED event, if slave returns > -EBUSY, i2c controller should issue RxCmdLast command to assert NAK > on the bus. That should be I2C_SLAVE_WRITE_RECEIVED and it should be NAKed on all errnos. Have you tested it?
On 14/05/2022 21:31, Wolfram Sang wrote: > On Fri, Apr 22, 2022 at 11:08:03AM +0700, Quan Nguyen wrote: >> When processing I2C_SLAVE_WRITE_REQUESTED event, if slave returns >> -EBUSY, i2c controller should issue RxCmdLast command to assert NAK >> on the bus. > > That should be I2C_SLAVE_WRITE_RECEIVED and it should be NAKed on all > errnos. Have you tested it? > Dear Wolfram, Thanks for the comment. Yes, we have tested this patch with ast2500 and see it works well without the need of the ugly slave_enable/disable() as before. When tested with ast2500, it is observed that there's always a I2C_SLAVE_WRITE_REQUESTED comes first then other I2C_SLAVE_WRITE_RECEIVED's follow for all transactions. In case slave is busy, the NAK will be asserted on the first occurrence of I2C_SLAVE_WRITE_REQUESTED make host to stop the current transaction (host later will retry with other transaction) until slave ready. This behavior is expected as we want host to drop all transactions while slave is busy on working on the response. That is why we choose to assert NAK on the first I2C_SLAVE_WRITE_REQUESTED of the transaction instead of I2C_SLAVE_WRITE_RECEIVED. As we are interested in this specific case, ie: to assert NAK only when slave busy, we dont want to force the current aspeed's slave to assert NAK in all errno's. That is why we choose to NAK only when there is an explicitly -EBUSY return from slave. Thank you for the review and hope to see further comments. Thanks, - Quan
Hi Quan, > When tested with ast2500, it is observed that there's always a > I2C_SLAVE_WRITE_REQUESTED comes first then other I2C_SLAVE_WRITE_RECEIVED's > follow for all transactions. Yes, that's the design of the interface :) > In case slave is busy, the NAK will be asserted on the first occurrence of > I2C_SLAVE_WRITE_REQUESTED make host to stop the current transaction (host > later will retry with other transaction) until slave ready. > > This behavior is expected as we want host to drop all transactions while > slave is busy on working on the response. That is why we choose to assert > NAK on the first I2C_SLAVE_WRITE_REQUESTED of the transaction instead of > I2C_SLAVE_WRITE_RECEIVED. From Documentation/i2c/slave-interface.rst: === About ACK/NACK -------------- It is good behaviour to always ACK the address phase, so the master knows if a device is basically present or if it mysteriously disappeared. Using NACK to state being busy is troublesome. SMBus demands to always ACK the address phase, while the I2C specification is more loose on that. Most I2C controllers also automatically ACK when detecting their slave addresses, so there is no option to NACK them. For those reasons, this API does not support NACK in the address phase. === So, the proper design is to NACK on the first received byte. All EEPROMs do it this way when they are busy because of erasing a page. All the best, Wolfram
On 16/06/2022 03:32, Wolfram Sang wrote: > Hi Quan, > >> When tested with ast2500, it is observed that there's always a >> I2C_SLAVE_WRITE_REQUESTED comes first then other I2C_SLAVE_WRITE_RECEIVED's >> follow for all transactions. > > Yes, that's the design of the interface :) > >> In case slave is busy, the NAK will be asserted on the first occurrence of >> I2C_SLAVE_WRITE_REQUESTED make host to stop the current transaction (host >> later will retry with other transaction) until slave ready. >> >> This behavior is expected as we want host to drop all transactions while >> slave is busy on working on the response. That is why we choose to assert >> NAK on the first I2C_SLAVE_WRITE_REQUESTED of the transaction instead of >> I2C_SLAVE_WRITE_RECEIVED. > > From Documentation/i2c/slave-interface.rst: > > === > > About ACK/NACK > -------------- > > It is good behaviour to always ACK the address phase, so the master knows if a > device is basically present or if it mysteriously disappeared. Using NACK to > state being busy is troublesome. SMBus demands to always ACK the address phase, > while the I2C specification is more loose on that. Most I2C controllers also > automatically ACK when detecting their slave addresses, so there is no option > to NACK them. For those reasons, this API does not support NACK in the address > phase. > > === > > So, the proper design is to NACK on the first received byte. All EEPROMs > do it this way when they are busy because of erasing a page. > Thanks Wolfram for the review. On the first occurrence of I2C_SLAVE_WRITE_REQUESTED, the address is already received with ACK. So if slave return -EBUSY, the NAK will occur on the next Rx byte (on I2C_SLAVE_WRITE_RECEIVED event). Tested this patch and capture using Saleae tool, it always shows ACK on the address and NAK on the first byte follow when slave return -EBUSY, ie: the byte follow the address, which is single part read command (0x03) in my case. + When slave return -EBUSY: S-> Aw(ACK)-> RxD(NAK)-> P 0x10 0x03 (Singlepart read) + When slave ready: S-> Aw(ACK)-> RxD(ACK)-> Sr-> Ar-> TxD(ACK)-> ... -> TxD(NAK)-> P 0x10 0x03 0x07 ... 0xDE Using the Logic 2 (with Saleae tool) to capture, we could see the log as below: write to 0x10 ack data: 0x03 <= when slave return -EBUSY write to 0x10 ack data: 0x03 <= when slave return -EBUSY write to 0x10 ack data: 0x03 <= when slave return -EBUSY ... write to 0x10 ack data: 0x03 <= when slave return -EBUSY write to 0x10 ack data: 0x03 <= when slave is ready read to 0x10 ack data: 0x07 0xF4 0x1D 0x00 0x01 0x00 0x00 0x00 0xDE Thanks, - Quan
Hi Quan, > On the first occurrence of I2C_SLAVE_WRITE_REQUESTED, the address is already > received with ACK. So if slave return -EBUSY, the NAK will occur on the next > Rx byte (on I2C_SLAVE_WRITE_RECEIVED event). This is exactly why I2C_SLAVE_WRITE_RECEIVED allows for an error code. From the docs: === * I2C_SLAVE_WRITE_RECEIVED (mandatory) 'val': bus driver delivers received byte 'ret': 0 if the byte should be acked, some errno if the byte should be nacked Another I2C master has sent a byte to us which needs to be set in 'val'. If 'ret' is zero, the bus driver should ack this byte. If 'ret' is an errno, then the byte should be nacked. === 'ret' is used to ACK/NACK the current byte in 'val'. That's exactly what you need, or? Does the aspeed driver not support acking the current byte?
On 16/06/2022 19:29, Wolfram Sang wrote: > Hi Quan, > >> On the first occurrence of I2C_SLAVE_WRITE_REQUESTED, the address is already >> received with ACK. So if slave return -EBUSY, the NAK will occur on the next >> Rx byte (on I2C_SLAVE_WRITE_RECEIVED event). > > This is exactly why I2C_SLAVE_WRITE_RECEIVED allows for an error code. > From the docs: > > === > > * I2C_SLAVE_WRITE_RECEIVED (mandatory) > > 'val': bus driver delivers received byte > > 'ret': 0 if the byte should be acked, some errno if the byte should be nacked > > Another I2C master has sent a byte to us which needs to be set in 'val'. If 'ret' > is zero, the bus driver should ack this byte. If 'ret' is an errno, then the byte > should be nacked. > > === > > 'ret' is used to ACK/NACK the current byte in 'val'. That's exactly what > you need, or? Does the aspeed driver not support acking the current > byte? > It is true that aspeed driver does not support acking the current byte. Setting ASPEED_I2CD_M_S_RX_CMD_LAST will take effect on the next Rx byte as per my observation. S-> Aw(ACK)-> RxD(ACK)-> Sr-> Ar-> TxD(ACK)-> ... -> TxD(NAK)-> P (1) (2) Currently, setting ASPEED_I2CD_M_S_RX_CMD_LAST in (1), on I2C_SLAVE_WRITE_REQUESTED event, will make the NAK happen in (2) and make the read stop. If setting ASPEED_I2CD_M_S_RX_CMD_LAST on (2), ie: on I2C_SLAVE_WRITE_RECEIVED event, the read from Master is never NAK because there is no next Rx byte and Master is already switch to read from Slave. I understands that the return of i2c_slave_event(slave, I2C_SLAVE_WRITE_REQUESTED, &value) is always 0 as in Documentation/i2c/slave-interface.rst. But with this case, this is the way to NAK on the first byte and I'm wonder if this particular case would be supported somehow. Thanks, -- Quan
On 17/06/2022 14:08, Quan Nguyen wrote: > On 16/06/2022 19:29, Wolfram Sang wrote: >> Hi Quan, >> >>> On the first occurrence of I2C_SLAVE_WRITE_REQUESTED, the address is >>> already >>> received with ACK. So if slave return -EBUSY, the NAK will occur on >>> the next >>> Rx byte (on I2C_SLAVE_WRITE_RECEIVED event). >> >> This is exactly why I2C_SLAVE_WRITE_RECEIVED allows for an error code. >> From the docs: >> >> === >> >> * I2C_SLAVE_WRITE_RECEIVED (mandatory) >> >> 'val': bus driver delivers received byte >> >> 'ret': 0 if the byte should be acked, some errno if the byte should >> be nacked >> >> Another I2C master has sent a byte to us which needs to be set in >> 'val'. If 'ret' >> is zero, the bus driver should ack this byte. If 'ret' is an errno, >> then the byte >> should be nacked. >> >> === >> >> 'ret' is used to ACK/NACK the current byte in 'val'. That's exactly what >> you need, or? Does the aspeed driver not support acking the current >> byte? >> > > It is true that aspeed driver does not support acking the current byte. > Setting ASPEED_I2CD_M_S_RX_CMD_LAST will take effect on the next Rx byte > as per my observation. > > S-> Aw(ACK)-> RxD(ACK)-> Sr-> Ar-> TxD(ACK)-> ... -> TxD(NAK)-> P > (1) (2) > > Currently, setting ASPEED_I2CD_M_S_RX_CMD_LAST in (1), on > I2C_SLAVE_WRITE_REQUESTED event, will make the NAK happen in (2) and > make the read stop. > > If setting ASPEED_I2CD_M_S_RX_CMD_LAST on (2), ie: on > I2C_SLAVE_WRITE_RECEIVED event, the read from Master is never NAK > because there is no next Rx byte and Master is already switch to read > from Slave. > > I understands that the return of > i2c_slave_event(slave, I2C_SLAVE_WRITE_REQUESTED, &value) is always 0 as > in Documentation/i2c/slave-interface.rst. But with this case, this is > the way to NAK on the first byte and I'm wonder if this particular case > would be supported somehow. > Dear Wolfram, From my particular case, as it seems not to be able to nak on the current byte on I2C_SLAVE_WRITE_RECEIVED event (i2c-aspeed), is it possible to somehow allow slave to return some errno on the I2C_SLAVE_WRITE_REQUESTED event so that bus driver knows what to do for the next incoming byte if slave is busy? As from the docs: === * I2C_SLAVE_WRITE_REQUESTED (mandatory) 'val': unused 'ret': always 0 Another I2C master wants to write data to us. This event should be sent once our own address and the write bit was detected. The data did not arrive yet, so there is nothing to process or return. Wakeup or initialization probably needs to be done, though. === As the "Wakeup or initialization probably needs to be done" in the slave side, in case slave is fail to either wake up or initialization or busy in this particular case, there is no way for slave to let the bus driver know the status if the 'ret' is always 0. I'm also agree that it should be always ack on I2C_SLAVE_WRITE_REQUESTED event (when the slave address matched and the write bit detected). But if slave know it is fail to either wakeup or initialization or busy, the bus driver should be able to automatically to nak on the first write incoming byte. Hence, my thinking is to change the above: 'ret': always 0 to: 'ret': 0 otherwise some errno if slave is busy or fail to wakeup or initialization Thank you and best regards, - Quan
diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c index 771e53d3d197..ebc2b92656c8 100644 --- a/drivers/i2c/busses/i2c-aspeed.c +++ b/drivers/i2c/busses/i2c-aspeed.c @@ -244,6 +244,7 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status) u32 command, irq_handled = 0; struct i2c_client *slave = bus->slave; u8 value; + int ret; if (!slave) return 0; @@ -311,7 +312,9 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status) break; case ASPEED_I2C_SLAVE_WRITE_REQUESTED: bus->slave_state = ASPEED_I2C_SLAVE_WRITE_RECEIVED; - i2c_slave_event(slave, I2C_SLAVE_WRITE_REQUESTED, &value); + ret = i2c_slave_event(slave, I2C_SLAVE_WRITE_REQUESTED, &value); + if (ret == -EBUSY) + writel(ASPEED_I2CD_M_S_RX_CMD_LAST, bus->base + ASPEED_I2C_CMD_REG); break; case ASPEED_I2C_SLAVE_WRITE_RECEIVED: i2c_slave_event(slave, I2C_SLAVE_WRITE_RECEIVED, &value);
When processing I2C_SLAVE_WRITE_REQUESTED event, if slave returns -EBUSY, i2c controller should issue RxCmdLast command to assert NAK on the bus. Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com> --- v7: + None v6: + New introduced in v6 [Quan] drivers/i2c/busses/i2c-aspeed.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)