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

From: Jean Delvare
Date: Thu Sep 09 2021 - 09:30:02 EST

Hi Sascha,

On Thu, 9 Sep 2021 07:38:22 -0400, Sasha Levin wrote:
> From: Heiner Kallweit <hkallweit1@xxxxxxxxx>
> [ 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@xxxxxxxxx>
> Tested-by: Jean Delvare <jdelvare@xxxxxxx>
> Signed-off-by: Wolfram Sang <wsa@xxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
> 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

Jean Delvare
SUSE L3 Support