RE: [PATCH v3 3/7] i2c: aspeed: Fix unhandled Tx done with NAK

[Ryan Chen <ryan_chen@aspeedtech.com>]

> -----Original Message-----
> From: Joel Stanley <joel@jms.id.au>
> Sent: Thursday, May 20, 2021 7:29 AM
> To: Quan Nguyen <quan@os.amperecomputing.com>; Ryan Chen
> <ryan_chen@aspeedtech.com>
> Cc: Corey Minyard <minyard@acm.org>; Rob Herring <robh+dt@kernel.org>;
> Andrew Jeffery <andrew@aj.id.au>; Brendan Higgins
> <brendanhiggins@google.com>; Benjamin Herrenschmidt
> <benh@kernel.crashing.org>; Wolfram Sang <wsa@kernel.org>; Philipp Zabel
> <p.zabel@pengutronix.de>; openipmi-developer@lists.sourceforge.net;
> devicetree <devicetree@vger.kernel.org>; Linux ARM
> <linux-arm-kernel@lists.infradead.org>; linux-aspeed
> <linux-aspeed@lists.ozlabs.org>; Linux Kernel Mailing List
> <linux-kernel@vger.kernel.org>; linux-i2c@vger.kernel.org; Open Source
> Submission <patches@amperecomputing.com>; Phong Vo
> <phong@os.amperecomputing.com>; Thang Q . Nguyen
> <thang@os.amperecomputing.com>; OpenBMC Maillist
> <openbmc@lists.ozlabs.org>
> Subject: Re: [PATCH v3 3/7] i2c: aspeed: Fix unhandled Tx done with NAK
> 
> Ryan, can you please review this change?
> 
> On Wed, 19 May 2021 at 07:50, Quan Nguyen
> <quan@os.amperecomputing.com> wrote:
> >
> > It is observed that in normal condition, when the last byte sent by
> > slave, the Tx Done with NAK irq will raise.
> > But it is also observed that sometimes master issues next transaction
> > too quick while the slave irq handler is not yet invoked and Tx Done
> > with NAK irq of last byte of previous READ PROCESSED was not ack'ed.
> > This Tx Done with NAK irq is raised together with the Slave Match and
> > Rx Done irq of the next coming transaction from master.
> > Unfortunately, the current slave irq handler handles the Slave Match
> > and Rx Done only in higher priority and ignore the Tx Done with NAK,
> > causing the complain as below:
> > "aspeed-i2c-bus 1e78a040.i2c-bus: irq handled != irq. expected
> > 0x00000086, but was 0x00000084"
> >
> > This commit handles this case by emitting a Slave Stop event for the
> > Tx Done with NAK before processing Slave Match and Rx Done for the
> > coming transaction from master.
> 
> It sounds like this patch is independent of the rest of the series, and can go in
> on it's own. Please send it separately to the i2c maintainers and add a suitable
> Fixes line, such as:
> 
>   Fixes: f9eb91350bb2 ("i2c: aspeed: added slave support for Aspeed I2C
> driver")
> 
> >
> > Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
> > ---
> > v3:
> >   + First introduce in v3 [Quan]
> >
> >  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 724bf30600d6..3fb37c3f23d4
> > 100644
> > --- a/drivers/i2c/busses/i2c-aspeed.c
> > +++ b/drivers/i2c/busses/i2c-aspeed.c
> > @@ -254,6 +254,11 @@ 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) {
> 
> Can you explain why you need to do this handing inside the SLAVE_MATCH
> case?
> 
> Could you instead move the TX_NAK handling to be above the SLAVE_MATCH
> case?
> 
> > +               if (irq_status & ASPEED_I2CD_INTR_TX_NAK &&
> > +                   bus->slave_state ==
> > + ASPEED_I2C_SLAVE_READ_PROCESSED) {
> 
> Either way, this needs a comment to explain what we're working around.
> 
> > +                       irq_handled |= ASPEED_I2CD_INTR_TX_NAK;
> > +                       i2c_slave_event(slave, I2C_SLAVE_STOP,
> &value);

According the patch assume slave receive TX_NAK will be go to SLAVE_STOP state?

> > +               }
> >                 irq_handled |= ASPEED_I2CD_INTR_SLAVE_MATCH;
> >                 bus->slave_state = ASPEED_I2C_SLAVE_START;
> >         }
> > --
> > 2.28.0
> >