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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
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|---|---|---|
| .. | ||
| algos | ||
| busses | ||
| muxes | ||
| i2c-boardinfo.c | ||
| i2c-core.c | ||
| i2c-core.h | ||
| i2c-dev.c | ||
| i2c-mux.c | ||
| i2c-slave-eeprom.c | ||
| i2c-smbus.c | ||
| i2c-stub.c | ||
| Kconfig | ||
| Makefile | ||