linux-kernel - [PATCH 0/5 v4] Fix sp5100_tco watchdog driver regression

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Date:   Thu, 22 Jun 2017 15:21:29 +0200
From:   Zoltán Böszörményi 
        <zboszor@...hu>
To:     linux-kernel@...r.kernel.org
Cc:     linux-usb@...r.kernel.org, linux-watchdog@...r.kernel.org,
        linux-i2c@...r.kernel.org,
        Paul Menzel <paulepanter@...rs.sourceforge.net>,
        Christian Fetzer <fetzer.ch@...il.com>,
        Jean Delvare <jdelvare@...e.com>,
        Nehal Shah <nehal-bakulchandra.shah@....com>,
        Tim Small <tim@...ss.co.uk>,
        Guenter Roeck <linux@...ck-us.net>, kernel@...ss.net,
        wim@...ana.be, jlayton@...chiereds.net, marc.2377@...il.com,
        cshorler@...glemail.com, wsa@...-dreams.de,
        regressions@...mhuis.info,
        Zoltán Böszörményi 
        <zboszor@...hu>
Subject: [PATCH 0/5 v4] Fix sp5100_tco watchdog driver regression

This patch series fixes a regression introduced by:

commit 2fee61d22e606fc99ade9079fda15fdee83ec33e
Author: Christian Fetzer <fetzer.ch@...il.com>
Date:   Thu Nov 19 20:13:48 2015 +0100

    i2c: piix4: Add support for multiplexed main adapter in SB800

The regression caused sp5100_tco fail to load:

sp5100_tco: SP5100/SB800 TCO WatchDog Timer Driver v0.05
sp5100_tco: PCI Vendor ID: 0x1002, Device ID: 0x4385, Revision ID: 0x42
sp5100_tco: I/O address 0x0cd6 already in use

Notable bugzilla links about this issue:
https://bugzilla.kernel.org/show_bug.cgi?id=170741
https://bugzilla.redhat.com/show_bug.cgi?id=1369269
https://bugzilla.redhat.com/show_bug.cgi?id=1406844

The previous two versions of this patch series introduced
a common mutex to synchronize access to the I/O port pair
0xcd6 / 0xcd7 used by the AMD SB800 USB PCI quirk code and
the i2c-piix and sp5100_tco drivers. The common mutex was
criticized because it introduces an inter-dependency between
drivers.

This approach modifies the request_muxed_region() semantics and
modifies the possible use cases.

The first patch in the series adds a new IORESOURCE_ALLOCATED
flag that alloc_resource() sets and free_resource() considers.
The core of __request_region() is factored out into a new function
that doesn't allocate. With this change, drivers can use the
pre-existing DEFINE_RES_IO_NAMED() static initialized macro
to declare struct resource statically (e.g. on the stack)
and pass the address of it to the new __request_declared_region()
function. A new macro called request_declared_muxed_region()
was added to exploit this functionality. Because of the new
IORESOURCE_ALLOCATED resource flag, release_region() can still
be called with the old interface (the port region start and
end values) and it won't attempt to free a non-allocated resource.
This eliminated one failure case that can come from allocation
errors.

The second patch modifies the behaviour of IORESOURCE_MUXED,
a.k.a. the request_*muxed_region() macros. When these macros
are called, the caller goes to sleep when there is any conflicting
regions, even if the conflicting region did not use the
IORESOURCE_MUXED flag. The kernel logs this inconsistent
flag usage with KERN_ERR. This change eliminates the second
failure case for IORESOURCE_MUXED and request_muxed_region()
can be used like mutex_lock(), i.e. it returns only in case it
could successfully request the region.

The last three patches adds proper synchronization between the
USB PCI quirks code and the i2c-piix and sp5100_tco drivers.

The result is that the sp5100_tco driver can load and works again:

sp5100_tco: SP5100/SB800 TCO WatchDog Timer Driver v0.05
sp5100_tco: PCI Vendor ID: 0x1002, Device ID: 0x4385, Revision ID: 0x42
sp5100_tco: Using 0xfed80b00 for watchdog MMIO address
sp5100_tco: Last reboot was not triggered by watchdog.
sp5100_tco: initialized (0xffffba2f4192db00). heartbeat=60 sec (nowayout=0)

Signed-off-by: Zoltán Böszörményi <zboszor@...hu>
---
 drivers/i2c/busses/i2c-piix4.c | 41 ++++++++++++-------------------------
 drivers/usb/host/pci-quirks.c  |  4 ++++
 drivers/watchdog/sp5100_tco.c  | 28 +++++++++++++------------
 include/linux/ioport.h         | 14 +++++++++++++
 kernel/resource.c              | 46 ++++++++++++++++++++++++++++++++++++++----
 5 files changed, 88 insertions(+), 45 deletions(-)