linux-kernel - Re: [PATCH] mfd: cros ec: spi: Fix "in progress" error signaling

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Date:   Tue, 14 Nov 2017 09:00:57 -0800
From:   Shawn N <shawnn@...omium.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
        Jon Hunter <jonathanh@...dia.com>,
        Benson Leung <bleung@...omium.org>
Subject: Re: [PATCH] mfd: cros ec: spi: Fix "in progress" error signaling

On Wed, Sep 27, 2017 at 3:19 PM, Brian Norris <briannorris@...omium.org> wrote:
> On Wed, Sep 27, 2017 at 02:35:27PM -0700, Shawn Nematbakhsh wrote:
>> For host commands that take a long time to process, cros ec can return
>> early by signaling a EC_RES_IN_PROGRESS result. The host must then poll
>> status with EC_CMD_GET_COMMS_STATUS until completion of the command.
>>
>> None of the above applies when data link errors are encountered. When
>> errors such as EC_SPI_PAST_END are encountered during command
>> transmission, it usually means the command was not received by the EC.
>> Treating such errors as if they were 'EC_RES_IN_PROGRESS' results is
>> almost always the wrong decision, and can result in host commands
>> silently being lost.
>>
>> Reported-and-tested-by: Jon Hunter <jonathanh@...dia.com>
>> Signed-off-by: Shawn Nematbakhsh <shawnn@...omium.org>
>> ---
>>  drivers/mfd/cros_ec_spi.c | 52 ++++++++++++++++++++++-------------------------
>>  1 file changed, 24 insertions(+), 28 deletions(-)
>
> I'm still not sure I understand the full extent of the
> originally-reported error (it's still likely a SPI transport issue?),
> but I believe this patch is good anyway:
>
> Reviewed-by: Brian Norris <briannorris@...omium.org>

Jon tracked down the root cause of the originally-reported error, but
we should still land this patch, as it fixes error signaling that was
previously broken.

>
> I wonder if we should tone down the BUG_ON()'s in drivers/mfd/cros_ec*
> and drivers/platform/chrome/* too. That's basically a no-no these days,
> as all of these type of things should be able to gracefully propagate
> errors, no matter how "unlikely" it should be to see a crazy protocol
> version number or a bad message length.