Re: [PATCH v2 RESEND 1/2] i2c: aspeed: Fix unhandled Tx done with NAK

Quan Nguyen
2023-11-29T09:03:20Z

On 29/11/2023 07:35, Andi Shyti wrote:
> Hi Quan,
>
> On Tue, Nov 28, 2023 at 02:52:35PM +0700, Quan Nguyen wrote:
>> Under normal conditions, after the last byte is sent by the Slave, the
>> TX_NAK interrupt is raised. However, it is also observed that
>> sometimes the Master issues the next transaction too quickly while the
>> Slave IRQ handler is not yet invoked and the TX_NAK interrupt for the
>> last byte of the previous READ_PROCESSED state has not been ack’ed.
>> This TX_NAK interrupt is then raised together with SLAVE_MATCH interrupt
>> and RX_DONE interrupt of the next coming transaction from Master. The
>> Slave IRQ handler currently handles the SLAVE_MATCH and RX_DONE, but
>> ignores the TX_NAK, causing complaints such as
>> "aspeed-i2c-bus 1e78a040.i2c-bus: irq handled != irq. Expected
>> 0x00000086, but was 0x00000084"
>>
>> This commit adds code to handle this case by emitting a SLAVE_STOP event
>> for the TX_NAK before processing the RX_DONE for the coming transaction
>> from the Master.
>>
>> Fixes: f9eb91350bb2 ("i2c: aspeed: added slave support for Aspeed I2C driver")
>> Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
>> ---
>> v2:
>> + Split to separate series [Joel]
>> + Added the Fixes line [Joel]
>> + Revised commit message [Quan]
>>
>> v1:
>> + First introduced in
>> https://lore.kernel.org/all/20210519074934.20712-1-quan@os.amperecomputing.com/
>> ---
>> drivers/i2c/busses/i2c-aspeed.c | 5 +++++
>> 1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
>> index 28e2a5fc4528..79476b46285b 100644
>> --- a/drivers/i2c/busses/i2c-aspeed.c
>> +++ b/drivers/i2c/busses/i2c-aspeed.c
>> @@ -253,6 +253,11 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
>>
>> /* Slave was requested, restart state machine. */
>> if (irq_status & ASPEED_I2CD_INTR_SLAVE_MATCH) {
>> + if (irq_status & ASPEED_I2CD_INTR_TX_NAK &&
>> + bus->slave_state == ASPEED_I2C_SLAVE_READ_PROCESSED) {
>> + irq_handled |= ASPEED_I2CD_INTR_TX_NAK;
>> + i2c_slave_event(slave, I2C_SLAVE_STOP, &value);
>> + }
>
> this is a duplicate of a later "if (...)" satement. What is the
> need for having them both?
>
Thanks Andi for the review.

I assumed the if statement you mentioned is here in [1]. If so, then
that is not duplicate.

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/i2c/busses/i2c-aspeed.c?h=v6.7-rc3#n287

The if statement is to process the case when Slave sending data to
Master but being NAK, the I2C_SLAVE_STOP event will emit later in
switch-case statement. But it is only for the case INTR_TX_NAK without
INTR_SLAVE_MATCH.

The new code is for the case of INTR_TX_NAK with INTR_SLAVE_MATCH. What
it does is to detect if there is a mix of INTR_TX_NAK of previous i2c
transaction and the start of new i2c transaction, indicate by
INTR_SLAVE_MATCH which is only raised when Slave found its address
matched on the first byte it received. If so, the new code will try to
emit the I2C_SLAVE_STOP first to complete the previous transaction and
process the rest as a new request.

So if this was the case (with INTR_SLAVE_MATCH), the INTR_RX_DONE should
always raise with INTR_SLAVE_MATCH because Slave did receive the data
which matched with its Slave address. And this will be translated into
either I2C_SLAVE_[READ|WRITE]_REQUESTED and that make the if statement
you mentioned [1] evaluate to false and skip.

So, in short, the new code is trying to handle the case of INTR_TX_NAK
with INTR_SLAVE_MATCH first before let the rest process as normal.

Thanks,
- Quan