linux-kernel - Re: [PATCH] cpufreq: suspend/resume governors with PM notifiers

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Date:	Thu, 21 Nov 2013 21:47:20 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	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>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [PATCH] cpufreq: suspend/resume governors with PM notifiers

On 21 November 2013 20:08, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Wednesday, November 20, 2013 11:04:28 AM Viresh Kumar wrote:
>> On 18 November 2013 11:09, viresh kumar <viresh.kumar@...aro.org> wrote:

>> > Because in our usecase, we just want to know when suspend has started or
>> > resume has finished. And so we really don't need a per cpu callback.
>
> But it won't hurt I suppose?

Hmm.. getting a single call to cpufreq core would be faster for sure. Otherwise
we need to mark all the calls leaving the first one as no-ops..

> That actually isn't correct.  On systems with ACPI the processor driver binds to
> those devices.  So the processor driver could use PM callbacks on those systems
> in principle.

> Introduce proper drivers for processors?  All of the cpuidle and cpufreq stuff
> currently works by using its own homegrown device registration methods etc, but
> surely that doesn't have to be the case?

Hmm.. So you are asking for a new cpu-driver which can be used by cpufreq and
cpuidle to get callback? If yes, where such driver will exist? And will the ACPI
processor-drivers exist parallely? Or something else?

>> > And I really feel even if we would be able to use cpu callbacks for
>> > suspend/resume, that would be a real *Hack*, because our framework doesn't want
>> > to get a callback for each of its devices (i.e. cpu) but a single callback at
>> > certain instances..
>
> Oh really?  So CPUs are not individual devices any more or what?

I am not calling cpu callbacks as hack but using them for cpufreq looked like
one to me.

Replying here to the other mail as well:

On 21 November 2013 20:09, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Monday, November 18, 2013 09:37:39 PM Lan Tianyu wrote:
>> Another point, I just see cpuidle_resume() and cpuidle_pause() are
>> called in the dpm_resume_noirq and dpm_suspend_noirq(). Not sure whether
>> this can be applied to cpufreq.
>
> I don't see why not.

Interesting. So you would be happy if I add such calls after freezing userspace
and before restoring it back for cpufreq?
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