Re: [PATCH AUTOSEL 5.14 088/252] i2c: i801: Fix handling SMBHSTCNT_PEC_EN

[Sasha Levin <sashal@kernel.org>]

On Thu, Sep 09, 2021 at 03:13:20PM +0200, Jean Delvare wrote:
>Hi Sascha,
>
>On Thu,  9 Sep 2021 07:38:22 -0400, Sasha Levin wrote:
>> From: Heiner Kallweit <hkallweit1@gmail.com>
>>
>> [ Upstream commit a6b8bb6a813a6621c75ceacd1fa604c0229e9624 ]
>>
>> Bit SMBHSTCNT_PEC_EN is used only if software calculates the CRC and
>> uses register SMBPEC. This is not supported by the driver, it supports
>> hw-calculation of CRC only (using bit SMBAUXSTS_CRCE). The chip spec
>> states the following, therefore never set bit SMBHSTCNT_PEC_EN.
>>
>> Chapter SMBus CRC Generation and Checking
>> If the AAC bit is set in the Auxiliary Control register, the PCH
>> automatically calculates and drives CRC at the end of the transmitted
>> packet for write cycles, and will check the CRC for read cycles. It will
>> not transmit the contents of the PEC register for CRC. The PEC bit must
>> not be set in the Host Control register. If this bit is set, unspecified
>> behavior will result.
>>
>> This patch is based solely on the specification and compile-tested only,
>> because I have no PEC-capable devices.
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> Tested-by: Jean Delvare <jdelvare@suse.de>
>> Signed-off-by: Wolfram Sang <wsa@kernel.org>
>> Signed-off-by: Sasha Levin <sashal@kernel.org>
>> ---
>>  drivers/i2c/busses/i2c-i801.c | 27 +++++++++++----------------
>>  1 file changed, 11 insertions(+), 16 deletions(-)
>
>This patch fixes a theoretical problem nobody has ever complained
>about. I don't think it makes sense to backport it to stable kernel
>branches.

Sure, I'll drop it. Thanks.

-- 
Thanks,
Sasha