Re: [PATCH v3] pwm: imx: Let PWM be active during suspend

[Thierry Reding <thierry.reding@gmail.com>]

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On Mon, Nov 20, 2017 at 09:27:23PM -0200, Fabio Estevam wrote:
> From: Fabio Estevam <fabio.estevam@nxp.com>
> 
> On a imx6q-cubox-i board, which has an LED driven by PWM, when the system
> goes into suspend the PWM block is disabled by default, then the PWM pin
> goes to logic level zero and turn on the LED during suspend, which is not
> really the behaviour we want to see.
> 
> By keeping the PWM enabled during suspend via STOPEN bit, the pwm-leds
> driver sets the brightness to zero in suspend and then the LED is
> turned off as expected.
> 
> So always set the STOPEN to fix the PWM behaviour in suspend.

It looks like this would also keep other PWMs enabled in suspend. If for
example you hooked up a fan to this PWM this change would make it so
that the fan would remain on during suspend. That doesn't sound
desirable to me.

On v2, I see this reply from you:

	Please note that on imx6qdl-cuboxi the pwm is active low.

I also see that imx6q-cubox-i uses the "fsl,imx27-pwm" compatible
version of this controller and that supports polarity inversion. I think
the correct thing to do here is to mark the PWM as inverted (according
to the DTS file it is actually the pwmleds node that has an active-low
property). If you invert the PWM you could add extra code to the PWM
driver to deal with this properly and set STOPEN only for inverted PWM
signals.

Thierry

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