linux-kernel - Re: [PATCH 2/2] cpufreq: make sure frequency transitions are serialized

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Message-ID: <CAKohponHLGsjTXA3XRRGM+CFpMrsgTuCx00YPrCbkST5drB-ng@mail.gmail.com>
Date:	Thu, 3 Oct 2013 11:06:13 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	"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>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Amit Daniel Kachhap <amit.daniel@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] cpufreq: make sure frequency transitions are serialized

On 26 September 2013 00:07, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> So the problem is real, but the fix seems to be of a "quick and dirty" kind.

Hmm..

> First of all, it looks like we need a clear "begin transition" call that
> I suppose drivers should execute from their .target() methods once they have
> decided to do a transition.  That would increment the "ongoing" counter etc.
>
> Second, we need a corresponding "end transition" call that would be executed
> whenever appropriate from the driver's perspective.

Hmm..

> Clearly, these two things should be independent of the notifiers and the
> notifications should only be done between "begin transition" and "end
> transition" and only by whoever called the "begin transition" to start with.

So, we need to have begin/end calls in cpufreq_out_of_sync() as well?
As that is sending notifications..

> Now, question is what should happen if "begin transition" is called when
> the previous transition hasn't been completed yet, should it block or should
> it fail?  There seem to be arguments for both, but I suppose blocking would be
> easier to implement.

Hmm.. I will repost this once my other patches are in now.. as that will
change ->target() routine for multiple drivers and things would be simple
to fix then..
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