path: root/Documentation
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authorJavier Martinez Canillas <javier@osg.samsung.com>2016-04-16 21:14:52 -0400
committerWolfram Sang <wsa@the-dreams.de>2016-04-22 15:31:54 +0200
commit10ff4c5239a137abfc896ec73ef3d15a0f86a16a (patch)
tree4174254b698974075a09fd0b2bd904230731b9cb /Documentation
parent609d5a1b2b35bb62b4b3750396e55453160c2a17 (diff)
i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared
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 34e81ad5f0b6 ("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> Cc: stable@kernel.org
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