linux-kernel - Re: [PATCH v3 3/7] i2c: aspeed: Fix unhandled Tx done with NAK

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Date:   Wed, 19 May 2021 23:28:37 +0000
From:   Joel Stanley <joel@....id.au>
To:     Quan Nguyen <quan@...amperecomputing.com>,
        Ryan Chen <ryan_chen@...eedtech.com>
Cc:     Corey Minyard <minyard@....org>, Rob Herring <robh+dt@...nel.org>,
        Andrew Jeffery <andrew@...id.au>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Wolfram Sang <wsa@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        openipmi-developer@...ts.sourceforge.net,
        devicetree <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-aspeed <linux-aspeed@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-i2c@...r.kernel.org,
        Open Source Submission <patches@...erecomputing.com>,
        Phong Vo <phong@...amperecomputing.com>,
        "Thang Q . Nguyen" <thang@...amperecomputing.com>,
        OpenBMC Maillist <openbmc@...ts.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@...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@...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);
> +               }
>                 irq_handled |= ASPEED_I2CD_INTR_SLAVE_MATCH;
>                 bus->slave_state = ASPEED_I2C_SLAVE_START;
>         }
> --
> 2.28.0
>