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

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Message-ID: <20170410103320.GG2957@lahna.fi.intel.com>
Date:   Mon, 10 Apr 2017 13:33:20 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     thierry.reding@...il.com, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org, clemens.gruber@...ruber.com,
        andriy.shevchenko@...ux.intel.com,
        Sven Van Asbroeck <TheSven73@...glemail.com>
Subject: Re: [PATCH 1/1] pwm: pca9685: fix gpio-only operation.

On Sun, Apr 09, 2017 at 12:11:24PM -0400, Sven Van Asbroeck wrote:
> gpio-only driver operation never clears the SLEEP bit, which can
> cause the gpios to become unusable.
> 
> Example:
> 1. user requests first pwm  ->      driver clears SLEEP bit
> 2. user frees last pwm      ->      driver sets SLEEP bit
> 3. user requests gpio
> 4. user switches gpio on    ->      output does not turn on
>                                     because SLEEP bit is set
> 
> Prevent this behaviour by keeping the SLEEP bit cleared
> for the lifetime of the driver instance.
> 
> Fixes: bccec89f0a35 ("Allow any of the 16 PWMs to be used as a GPIO")
> Signed-off-by: Sven Van Asbroeck <TheSven73@...glemail.com>

How about implementing a real runtime PM in the driver? Then when the
device is idle regardless of whether it is GPIO or PWM, the SLEEP bit is
set and cleared accordingly.