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

[Sasha Levin]

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@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
> branches.

Sure, I'll drop it. Thanks.

--
Thanks,
Sasha