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

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Date:   Wed, 27 Sep 2017 15:19:09 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Shawn Nematbakhsh <shawnn@...omium.org>
Cc:     linux-kernel@...r.kernel.org, lee.jones@...aro.org,
        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 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>

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.