Re: [PATCH] i2c: xiic: Don't try to handle more interrupt events after error

From: Andi Shyti <andi.shyti@kernel.org>
To: Robert Hancock <robert.hancock@calian.com>
Cc: Michal Simek <michal.simek@amd.com>,
	Shubhrajyoti Datta <shubhraj@xilinx.com>,
	Wolfram Sang <wsa@kernel.org>, Marek Vasut <marex@denx.de>,
	linux-arm-kernel@lists.infradead.org, linux-i2c@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] i2c: xiic: Don't try to handle more interrupt events after error
Date: Tue, 6 Jun 2023 21:24:53 +0200	[thread overview]
Message-ID: <20230606192453.zjzz4kt76kus5hr5@intel.intel> (raw)
In-Reply-To: <20230606182558.1301413-1-robert.hancock@calian.com>

Hi Robert,

On Tue, Jun 06, 2023 at 12:25:58PM -0600, Robert Hancock wrote:
> In xiic_process, it is possible that error events such as arbitration
> lost or TX error can be raised in conjunction with other interrupt flags
> such as TX FIFO empty or bus not busy. Error events result in the
> controller being reset and the error returned to the calling request,
> but the function could potentially try to keep handling the other
> events, such as by writing more messages into the TX FIFO. Since the
> transaction has already failed, this is not helpful and will just cause
> issues.

what kind of issues?

> This problem has been present ever since:
> 
> commit 7f9906bd7f72 ("i2c: xiic: Service all interrupts in isr")
> 
> which allowed non-error events to be handled after errors, but became
> more obvious after:
> 
> commit 743e227a8959 ("i2c: xiic: Defer xiic_wakeup() and
> __xiic_start_xfer() in xiic_process()")
> 
> which reworked the code to add a WARN_ON which triggers if both the
> xfer_more and wakeup_req flags were set, since this combination is
> not supposed to happen, but was occurring in this scenario.
> 
> Skip further interrupt handling after error flags are detected to avoid
> this problem.
> 
> Fixes: 7f9906bd7f72 ("i2c: xiic: Service all interrupts in isr")
> Signed-off-by: Robert Hancock <robert.hancock@calian.com>

please add:

Cc: <stable@vger.kernel.org> # v4.3+

> ---
>  drivers/i2c/busses/i2c-xiic.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
> index 8a3d9817cb41..ee6edc963dea 100644
> --- a/drivers/i2c/busses/i2c-xiic.c
> +++ b/drivers/i2c/busses/i2c-xiic.c
> @@ -721,6 +721,8 @@ static irqreturn_t xiic_process(int irq, void *dev_id)
>  			wakeup_req = 1;
>  			wakeup_code = STATE_ERROR;
>  		}
> +		/* don't try to handle other events */
> +		goto out;

why don't we have goto's after every irq evaluation but only
here? Do the issues you mentioned happen olny in this particular
error case?

Thanks,
Andi

>  	}
>  	if (pend & XIIC_INTR_RX_FULL_MASK) {
>  		/* Receive register/FIFO is full */
> -- 
> 2.40.1
> 