Re: [PATCH] platform/chrome: cros_ec_proto: Send command again when timeout occurs

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, May 18, 2021 at 10:48:23AM +0200, Patryk Duda wrote:
> Sometimes kernel is trying to probe Fingerprint MCU (FPMCU) when it
> hasn't initialized SPI yet. This can happen because FPMCU is restarted
> during system boot and kernel can send message in short window
> eg. between sysjump to RW and SPI initialization.
> 
> Cc: <stable@vger.kernel.org> # 4.4+
> Signed-off-by: Patryk Duda <pdk@semihalf.com>
> ---
> Fingerprint MCU is rebooted during system startup by AP firmware (coreboot).
> During cold boot kernel can query FPMCU in a window just after jump to RW
> section of firmware but before SPI is initialized. The window was
> shortened to <1ms, but it can't be eliminated completly.
> 
> Communication with FPMCU (and all devices based on EC) is bi-directional.
> When kernel sends message, EC will send EC_SPI* status codes. When EC is
> not able to process command one of bytes will be eg. EC_SPI_NOT_READY.
> This mechanism won't work when SPI is not initailized on EC side. In fact,
> buffer is filled with 0xFF bytes, so from kernel perspective device is not
> responding. To avoid this problem, we can query device once again. We are
> already waiting EC_MSG_DEADLINE_MS for response, so we can send command
> immediately.
> 
> Best regards,
> Patryk
>  drivers/platform/chrome/cros_ec_proto.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>