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linux/drivers/i2c
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Javier Martinez Canillas a3db726d7e i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared 
commit 10ff4c5239 upstream.

The exynos5 I2C controller driver always prepares and enables a clock
before using it and then disables unprepares it when the clock is not
used anymore.

But this can cause a possible ABBA deadlock in some scenarios since a
driver that uses regmap to access its I2C registers, will first grab
the regmap lock and then the I2C xfer function will grab the prepare
lock when preparing the I2C clock. But since the clock driver also
uses regmap for I2C accesses, preparing a clock will first grab the
prepare lock and then the regmap lock when using the regmap API.

An example of this happens on the Exynos5422 Odroid XU4 board where a
s2mps11 PMIC is used and both the s2mps11 regulators and clk drivers
share the same I2C regmap.

The possible deadlock is reported by the kernel lockdep:

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(sec_core:428:(regmap)->lock);
                                lock(prepare_lock);
                                lock(sec_core:428:(regmap)->lock);
   lock(prepare_lock);

  *** DEADLOCK ***

Fix it by leaving the code prepared on probe and use {en,dis}able in
the I2C transfer function.

This patch is similar to commit 34e81ad5f0 ("i2c: s3c2410: fix ABBA
deadlock by keeping clock prepared") that fixes the same bug in other
driver for an I2C controller found in Samsung SoCs.

Reported-by: Anand Moon <linux.amoon@gmail.com>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Reviewed-by: Anand Moon <linux.amoon@gmail.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
History 2016-06-15 21:29:26 +01:00
..
algos Merge branch 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux 2014-01-29 19:56:20 -08:00
busses i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared 2016-06-15 21:29:26 +01:00
muxes i2c: mux: pca954x: fix dependencies 2014-06-27 14:27:19 +02:00
i2c-boardinfo.c i2c: Update the FSF address 2012-03-26 21:47:19 +02:00
i2c-core.c Revert "i2c: Mark adapter devices with pm_runtime_no_callbacks" 2015-05-18 11:03:21 +01:00
i2c-core.h i2c: Update the FSF address 2012-03-26 21:47:19 +02:00
i2c-dev.c i2c: i2c-dev: Create 'name' attribute automatically 2013-09-30 06:02:31 +02:00
i2c-mux.c i2c: mux: Inherit retry count and timeout from parent for muxed bus 2013-12-12 22:39:28 +01:00
i2c-smbus.c Update Jean Delvare's e-mail address 2014-01-29 20:40:08 +01:00
i2c-stub.c Update Jean Delvare's e-mail address 2014-01-29 20:40:08 +01:00
Kconfig Remove GENERIC_HARDIRQ config option 2013-09-13 15:09:52 +02:00
Makefile i2c-stub: Move to drivers/i2c 2012-10-28 21:37:00 +01:00