Re: [PATCH v2] pwm: pca9685: fix pwm/gpio inter-operation

From: Mika Westerberg
Date: Wed Jun 05 2019 - 08:58:01 EST

On Tue, Jun 04, 2019 at 02:13:45PM -0400, Sven Van Asbroeck wrote:
> This driver allows pwms to be requested as gpios via gpiolib.
> Obviously, it should not be allowed to request a gpio when its
> corresponding pwm is already requested (and vice versa).
> So it requires some exclusion code.
> Given that the pwm and gpio cores are not synchronized with
> respect to each other, this exclusion code will also require
> proper synchronization.
> Such a mechanism was in place, but was inadvertently removed
> by Uwe's clean-up patch.
> Upon revisiting the synchronization mechanism, we found that
> theoretically, it could allow two threads to successfully
> request conflicting pwms / gpios.
> Replace with a bitmap which tracks pwm in-use, plus a mutex.
> As long as pwm and gpio's respective request/free functions
> modify the in-use bitmap while holding the mutex, proper
> synchronization will be guaranteed.
> Reported-by: YueHaibing <yuehaibing@xxxxxxxxxx>
> Fixes: e926b12c611c ("pwm: Clear chip_data in pwm_put()")
> Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>

Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>