linux-kernel - Re: [PATCH 2/4] pwm: stm32-lp: Add power management support

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Date:   Wed, 6 Feb 2019 13:55:45 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:     Fabrice Gasnier <fabrice.gasnier@...com>, jic23@...nel.org,
        robh+dt@...nel.org, mark.rutland@....com, alexandre.torgue@...com,
        mcoquelin.stm32@...il.com, linux-iio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        vilhelm.gray@...il.com, linux-stm32@...md-mailman.stormreply.com,
        Tomasz Duszynski <tduszyns@...il.com>
Subject: Re: [PATCH 2/4] pwm: stm32-lp: Add power management support

On Wed, Feb 06, 2019 at 09:54:05AM +0100, Uwe Kleine-König wrote:
> On Wed, Feb 06, 2019 at 09:42:48AM +0100, Fabrice Gasnier wrote:
> > If you agree with the current approach, I can send a V2 with Tomasz's
> > suggestion to remove the ifdefs and use __maybe_unused instead.
> 
> I think the suspend callback should have something like:
> 
> 	if (is_still_enabled) {
> 		/*
> 		 * The consumer didn't stop us, so refuse to suspend.
> 		 */
> 		dev_err(dev, "The consumer didn't stop us, so refuse to suspend.\n");
> 		return -EBUSY;
> 	}
> 
> This way there are no bad surprises if the pwm is suspended before its
> consumer and it's obvious what is missing.

Something that just occurred to me: perhaps as part of pwm_get() we
should track where we were being requested from so that we could give
hints in situations like this as to where the consumer is that forgot
to suspend the PWM.

I suppose we already have pwm_device.label to help with this, but
perhaps we could improve things if we stored __builtin_return_address
during pwm_get() to help users pinpoint where they need to look.

Thierry

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