Re: [Regression] Changes to i2c-piix4.c initialisation prevent loading of sp5100_tco watchdog driver on AMD SB800 chipset

[Guenter Roeck]

Hi Paul,

On 03/31/2017 12:17 AM, Paul Menzel wrote:
> Dear Wolfram,
>
>
> Thank you for the reply, which we talked about briefly at the
> Chemnitzer LinuxTage.
>
>
> Am Freitag, den 03.03.2017, 11:17 +0100 schrieb Wolfram Sang:
> > > Unfortunately, commit 2fee61d22e (i2c: piix4: Add support for
> > > multiplexed main adapter in SB800) [1] caused a regression. Tim
> > > reported that to the Linux Kernel Bugtracker as bug #170741 last
> > > September [2], but it looks like the affected subsystems donât use it.
> >
> > Jean Delvare pointed out this issue amongst others[1] last year already.
> > Let me quote:
> >
> > ===
> >
> > 5* The I/O ports used for SMBus configuration and port switching are
> > also needed by a watchdog driver, sp5100_tco. Both drivers request the
> > region, so the first one wins, and the other driver can't be loaded.
> > sp5100_tco was there first, so the changes done to the i2c-piix4 driver
> > recently will cause a regression for some users by preventing them
> > from using the sp5100_tco and i2c-piix4 drivers at the same time. In
> > the long run I guess we will need a helper module to handle this shared
> > resource. Unless IORESOURCE_MUXED can be used for that. Either way,
> > that's more work than I can put into this before kernel v4.5 is
> > released. For the time being, I think we should simply make it
> > non-fatal if the I/O ports can't be requested, and continue without
> > multiplexing (as before.)
> >
> > ===
> >
> > Seems nobody had the resources, so far.
>
> I still donât understand, why Jean then not immediately reverted the
> commit to adhere to the Linux Kernelâs no-regression-policy.
>
> > I don't have the HW and not much experience with non-embedded
> > platforms. I wonder, though, if we really need to convert the drivers
> > to MFD ones, or if we could use the simpler MFD_SYSCON mechanism
> > which helps in exactly such cases for embedded platforms. But I am
> > really lacking details here and am afraid this is probably all the
> > input I can give currently.
>
> Zoltan stepped up, and uploaded a patch for review to the Kernel.org
> Bugzilla [2], also attached to this message.

Please don't send patches as attachments.

request_muxed_region() can fail, and literally every other driver
using it checks for that failure. Please do the same.

The sp5100_tco_dev_name change in the watchdog driver is unnecessary.
There are some unnecessary { } in the watchdog driver after the patch
is applied.

Please split the patch into two patches so they can be reviewed and
applied separately.

Thanks,
Guenter