linux-kernel - Re: [Regression] Changes to i2c-piix4.c initialisation prevent loading of sp5100

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Date:   Fri, 3 Mar 2017 11:17:02 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Paul Menzel <paulepanter@...rs.sourceforge.net>
Cc:     Christian Fetzer <fetzer.ch@...il.com>,
        Jean Delvare <jdelvare@...e.com>, linux-i2c@...r.kernel.org,
        linux-watchdog@...r.kernel.org, 853122@...s.debian.org,
        Wim Van Sebroeck <wim@...ana.be>,
        Guenter Roeck <linux@...ck-us.net>,
        Tim Small <tim@...ss.co.uk>,
        Nehal Shah <nehal-bakulchandra.shah@....com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Brandon <tbrandonau@...il.com>,
        Eddi De Pieri <eddi@...ieri.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [Regression] Changes to i2c-piix4.c initialisation prevent
 loading of sp5100_tco watchdog driver on AMD SB800 chipset

> 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 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.

Regards,

   Wolfram

[1] http://www.spinics.net/lists/linux-i2c/msg23437.html

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