linux-kernel - [PATCH v3 0/1] pwm: pca9685: fix gpio-only operation.

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Date:   Wed, 12 Apr 2017 11:15:58 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     thierry.reding@...il.com
Cc:     linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
        clemens.gruber@...ruber.com, mika.westerberg@...ux.intel.com,
        andriy.shevchenko@...ux.intel.com
Subject: [PATCH v3 0/1] pwm: pca9685: fix gpio-only operation.

Mika, I investigated what's required to suspend the device on remove,
by compiling as a module and running insmod/rmmod in various
circumstances.

As you suspected, pm_runtime_suspend() is unneccessary. I removed it,
and the chip is suspended ok when the module unloads. But this could be
because the pm_runtime refcnt is always zero when _remove() is called ?

When unloading the module (rmmod) :
If a gpio is still exported, the kernel unexports the gpio before calling
_remove().
If a pwm is still exported, the kernel refuses to rmmod the module. Even
'rmmod -f' does not work.

I am not sure if the kernel will ever call _unload() without releasing
the associated pwms/gpios. And if it ever does, I am also not sure how
we could convince pm_runtime to go to suspend.

v3:
	remove unnecessary call to pm_runtime_suspend()

	fix coding style for multi-line comment
	(checkpatch.pl should ideally catch this, but did not?)

v2:
	the pm_runtime framework controls the SLEEP bit, as suggested by
	Mika Westerberg.

v1:
	the SLEEP bit is always on.

Sven Van Asbroeck (1):
  pwm: pca9685: fix gpio-only operation.

 drivers/pwm/pwm-pca9685.c | 111 ++++++++++++++++++++++++++++++++--------------
 1 file changed, 78 insertions(+), 33 deletions(-)

-- 
1.9.1