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 don’t 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 don’t understand, why Jean then not immediately reverted the
commit to adhere to the Linux Kernel’s 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.

Christian, Tim, and Nehal could you please test and review it?


Thanks,

Paul


> [1] http://www.spinics.net/lists/linux-i2c/msg23437.html
[2] https://bugzilla.kernel.org/show_bug.cgi?id=170741