On Mon, Jan 19, 2015 at 05:03:33PM +0100, Paul Osmialowski wrote: > This patch solves deadlock between clock prepare mutex and regmap mutex reported > by Tomasz Figa in [1] by implementing solution from [2]: "always leave the clock > of the i2c controller in a prepared state". > > [1] https://lkml.org/lkml/2014/7/2/171 > [2] https://lkml.org/lkml/2014/7/2/207 > > On each i2c transfer handled by s3c24xx_i2c_xfer(), clk_prepare_enable() was > called, which calls clk_prepare() then clk_enable(). clk_prepare() takes > prepare_lock mutex before proceeding. Note that i2c transfer functions are > invoked from many places in kernel, typically with some other additional lock > held. > > It may happen that function on CPU1 (e.g. regmap_update_bits()) has taken a > mutex (i.e. regmap lock mutex) then it attempts i2c communication in order to > proceed (so it needs to obtain clock related prepare_lock mutex during transfer > preparation stage due to clk_prepare() call). At the same time other task on > CPU0 wants to operate on clock (e.g. to (un)prepare clock for some other reason) > so it has taken prepare_lock mutex. > > CPU0: CPU1: > clk_disable_unused() regulator_disable() > clk_prepare_lock() map->lock(map->lock_arg) > regmap_read() s3c24xx_i2c_xfer() > map->lock(map->lock_arg) clk_prepare_lock() > > Implemented solution from [2] leaves i2c clock prepared. Preparation is done in > s3c24xx_i2c_probe() function. Without this patch, it is immediately unprepared > by clk_disable_unprepare() call. I've replaced this call with clk_disable() and > I've added clk_unprepare() call in s3c24xx_i2c_remove(). > > The s3c24xx_i2c_xfer() function now uses clk_enable() instead of > clk_prepare_enable() (and clk_disable() instead of clk_unprepare_disable()). > > Signed-off-by: Paul Osmialowski <p.osmialowsk@xxxxxxxxxxx> Applied to for-current, thanks!
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