linux-kernel - Re: [PATCH V2 1/2] cpufreq: suspend governors on system suspend/hibernate

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Message-ID: <1569441.L2JJETg4Jp@vostro.rjw.lan>
Date:	Wed, 27 Nov 2013 15:26:49 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Pavel Machek <pavel@....cz>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Patch Tracking <patches@...aro.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lan Tianyu <tianyu.lan@...el.com>, Nishanth Menon <nm@...com>,
	jinchoi@...adcom.com,
	Sebastian Capella <sebastian.capella@...aro.org>
Subject: Re: [PATCH V2 1/2] cpufreq: suspend governors on system suspend/hibernate

On Wednesday, November 27, 2013 08:26:00 AM Viresh Kumar wrote:
> On 27 November 2013 01:48, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > On Tuesday, November 26, 2013 08:39:02 PM Pavel Machek wrote:
> >> So... we freeze frequencies in whatever state they are, yes?
> 
> Better go through the V3 of this patchset:
> 
> https://lkml.org/lkml/2013/11/25/838
> 
> We are giving drivers and opportunity to set core to whatever frequency they
> want before suspending.
> 
> > Yes.  The idea was to do that after suspending devices in which case it wouldn't
> > matter so much.  But Viresh always has to complicate things.
> 
> :)
> 
> Its complicated by the kind of designs we have for our hardware. We tried the
> noirq callbacks and it worked atleast for Nishanth, who reported the problem
> initially. But the problem started when drivers wanted to change their
> frequencies before suspending and that can't happen in noirq place..

This way you end up with a fix that may introduce other issues.  Which is kind
of fine before a merge window, but not so much after one.  So at this point it's
better to fix things that may be fixed without introducing those other issues
*first* and then go for a more intrusive change that will cover more cases.

> I had another idea but then left it thinking that it might be even more
> complicated :)
> 
> What about both dpm_suspend_noirq and dpm_suspend callbacks. Drivers
> will change freq in dpm_suspend_noirq and dpm_suspend will stop governors?
> 
> But the question is can governors try another frequency at that time?
> i.e. override whatever is configured by drivers?
> 
> >> Should we go to some specific frequency?
> >
> > If that is done where it is done, yes, we should.
> 
> You meant dpm_suspend() here, right?

Yes.

Thanks!

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