linux-kernel - Re: [PATCH V2] cpufreq: Make sure CPU is running on a freq from freq-table

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Message-ID: <CAKohpok0QJ2xP5uoSaAsX76KwD5yi9Z54pgNyQ7CW3c4Fkbq2A@mail.gmail.com>
Date:	Mon, 25 Nov 2013 22:31:56 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Dirk Brandewie <dirk.brandewie@...il.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	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>,
	Nishanth Menon <nm@...com>, Carlos Hernandez <ceh@...com>
Subject: Re: [PATCH V2] cpufreq: Make sure CPU is running on a freq from freq-table

On 25 November 2013 22:08, Dirk Brandewie <dirk.brandewie@...il.com> wrote:
> IMHO this issue should be fixed in the scaling driver for the platform.
>
> The scaling driver sets policy->cur and fills in the frequency table and has

Not anymore, policy->cur is set in the core for most of the drivers now.
Drivers just provide ->get() callbacks.

> the ability to adjust the frequency of the CPU.

I believe this kind of decisions should stay with the core, drivers should
just provide the backend instead of intelligence..

> Letting this leak up into the core
> is wrong IMHO and just widens the window where the CPU will be running at
> the wrong frequency set by the bootloader.

It doesn't stay there for long enough.. we get to this point in
cpufreq core just
after calling ->init(), and if the CPU is working without issues until
now, it will
stay stable for few more milliseconds.

> Shouldn't there be a check to see if the problem exists at all?  Otherwise
> the core is setting a policy for ALL platform even those where the issue
> does
> not exist.

That is taken care of by __cpufreq_driver_target(). It checks if we are
already running at requested frequency or not (after getting the next
higher frequency)... If current freq is present in table,
cpufreq_frequency_table_target() will return current frequency only for
policy->cur -1. And so we will not end up configuring hardware
unnecessarily.
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