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

[Quan Nguyen]

On 30/11/2023 04:25, Andi Shyti wrote:
> Hi Quan,
>
> > 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@xxxxxxxxxxxxxxxxxxxxxx>
> > > > ---
> > > > 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@xxxxxxxxxxxxxxxxxxxxxx/
> > > > ---
> > > >    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.
>
> yes, I saw that, but wasn't it easier to do something like this:
>
> 	if (irq_status & ASPEED_I2CD_INTR_TX_NAK &&
> 	    bus->slave_state == ASPEED_I2C_SLAVE_READ_PROCESSED) {
> 		irq_handled |= ASPEED_I2CD_INTR_TX_NAK;
> 		bus->slave_state = ASPEED_I2C_SLAVE_STOP;
>
> 		if (irq_status & ASPEED_I2CD_INTR_SLAVE_MATCH)
> 			i2c_slave_event(slave, I2C_SLAVE_STOP, &value);
>
> 	}
>
> But I see that Andrew has done some similar comment, also for
> patch 2. You can answer both in the same mail, not to duplicate
> the answer :-)
>
> We can wait for him to reply.

I think Andrew's idea to handle the STOP conditions prior is much 
better. Will test and post the next version ASAP.

Thanks a lot for the review
- Quan