linux-kernel - Re: [PATCH V3] PM / devfreq: tie suspend/resume to runtime-pm

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Date:	Sun, 05 May 2013 13:48:09 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Rajagopal Venkat <rajagopal.venkat@...aro.org>
Cc:	myungjoo.ham@...sung.com, Kevin Hilman <khilman@...aro.org>,
	Alan Stern <stern@...land.harvard.edu>, patches@...aro.org,
	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] PM / devfreq: tie suspend/resume to runtime-pm

On Wednesday, April 17, 2013 06:58:21 PM Rajagopal Venkat wrote:
> Devfreq core runtime suspend/resume of a device is explicitly
> handled by devfreq driver using devfreq_suspend_device() and
> devfreq_resume_device() apis typically called from runtime
> suspend/resume callbacks. This patch aims to take away this
> from devfreq drivers and handle it from runtime-pm core. So
> that devfreq core runtime suspend/resume of a device is
> automatically done with runtime pm suspend/resume. The devfreq
> drivers shouldn't be concerned on when to suspend/resume the
> devfreq.

I agree, but perhaps there's a better way to achieve that than fumbling
in the PM core?

Did you consider using a PM domain for that?

> This patch is targeted to handle devfreq core load monitoring
> runtime suspend/resume only. Not the actual hardware itself.
> All the resources like clocks and regulators must still be
> handled by device driver using runtime-pm. The sequence of
> devfreq and device runtime suspend/resume is,
> 
> pm_runtime_suspend(dev) will first suspend device devfreq
> (if available) before device is suspended to ensure devfreq load
> monitoring is stopped and no device resources like clocks are
> accessed while device suspend is in progress.
> 
> pm_runtime_resume(dev) will resume device devfreq(if available)
> after device is resumed to ensure device resources like clocks
> are ready for use.
> 
> As devfreq runtime suspend/resume is done automatically from runtime
> core, this patch removes the existing devfreq_suspend_device() and
> devfreq_resume_device() apis.
> 
> Signed-off-by: Rajagopal Venkat <rajagopal.venkat@...aro.org>

I'm having a problem with this patch, because it's adding overhead into
rpm_suspend() and rpm_resume() for all devices, even though many of them
may not use devfreq.  Worse yet, there are systems in which devfreq will
never be used at all.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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