linux-kernel - Re: [PATCH V4 3/3] cpufreq: Tegra: implement intermediate frequency callbacks

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Message-ID: <CAKohpomdOEspgfxNR5p=PVLCeSUYcUWZ2cWGGQo0b__ptKiYtw@mail.gmail.com>
Date:	Fri, 23 May 2014 09:35:28 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arvind Chauhan <arvind.chauhan@....com>,
	Stephen Warren <swarren@...dia.com>,
	Doug Anderson <dianders@...omium.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Thomas Abraham <thomas.abraham@...aro.org>,
	Peter De Schrijver <pdeschrijver@...dia.com>
Subject: Re: [PATCH V4 3/3] cpufreq: Tegra: implement intermediate frequency callbacks

On 22 May 2014 22:09, Stephen Warren <swarren@...dotorg.org> wrote:
> I think the call to tegra_target_intermediate() is wrong here; shouldn't
> the cpufreq core guarantee that tegra_target_intermediate() has always
> been called before tegra_target(), so there's no need to repeat that
> call here?

That's what Doug requested in the previous version. get_intermediate()
can return zero in case drivers don't want to switch to intermediate
frequency for some target frequency.

Core should rather guarantee that target_index() is always called, if you
want core to guarantee that target_intermediate() is also always called,
then don't ever return zero from get_intermediate.

I did it that way for tegra as both target_intermediate() & target_index()
would have tried to set the same frequency for this particular case,
i.e. when target freq == intermediate frequency.

And both would have sent notification and the last notification wouldn't
have made any sense, both old-freq & new-freq would have been
intermediate freqs.

So, yes I see the feature suggested by Doug quite useful. Like in your
case.

> Also, tegra_target() doesn't seem to follow the rule documented by patch
> 2/3 that states ->target() should restore the orignal frequency on
> error. I'm not even sure if that's possible in general.

I thought I took care of that. Can you please give some example when
we aren't restoring original frequency on failure ?

About the rule, that has to be the expectation from core as there is no
way out that for core to know what happened at end of target_index()..

It can call get_rate() but that would be over engineering it looks ..
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