On 6/25/2015 2:35 AM, Nicolas Boichat wrote:
From: Antti Palosaari crope@iki.fi
Lockdep validator complains about recursive locking and deadlock when two different regmap instances are called in a nested order. That happens anytime a regmap read/write call needs to access another regmap.
This is because, for performance reason, lockdep groups all locks initialized by the same mutex_init() in the same lock class. Therefore all regmap mutexes are in the same lock class, leading to lockdep "nested locking" warnings if a regmap accesses another regmap. However, depending on the specifics of the driver, this can be perfectly safe (e.g. if there is a clear hierarchy between a "master" regmap that uses another "slave" regmap). In these cases, the warning is false and should be silenced.
As a solution, add configuration option to pass custom lock class key for lockdep validator, to be used in the regmap that needs to access another regmap. This removes the need for uglier workarounds in drivers, just to silence this warning (e.g. add custom mutex lock/unlock functions).
wouldn't it be better to use the mutex_lock_nested() and co to explicitly express your hierarchy?