linux-kernel - Re: [PATCH 1/2] cpufreq: Return error if ->get() failed in cpufreq_update

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Message-ID: <CAKohpo=mQWxoKTduR8FrrB4Qz45qXQrJjSudq=FkCJtHBTbo2Q@mail.gmail.com>
Date:	Mon, 17 Feb 2014 14:09:03 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.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>,
	Pierre Ossman <pierre-list@...man.eu>
Subject: Re: [PATCH 1/2] cpufreq: Return error if ->get() failed in cpufreq_update_policy()

On 17 February 2014 13:49, Srivatsa S. Bhat
<srivatsa.bhat@...ux.vnet.ibm.com> wrote:
> Quick question: Looking at cpufreq_update_policy() and cpufreq_out_of_sync(),
> I understand that if the cpufreq subsystem's notion of the current frequency
> does not match with the actual frequency of the CPU, it tries to adjust and
> notify everyone that the current frequency is so-and-so, as read from the
> hardware. Instead, why can't we simply set the frequency to the value that
> we _want_ it to be at? I mean, if cpufreq subsystem thinks it is X KHz and
> the actual frequency is Y KHz, we can as well fix the anomaly by setting the
> frequency immediately to X KHz right?
>
> The reason I ask this is that, if we follow this approach, then we can avoid
> ambiguities in dealing with the out-of-sync situation. That is, it becomes
> very straightforward to decide _what_ to do, when we detect scenarios where
> the frequency goes out of sync.

Hmm, it is just about doing all that stuff in a single line, like:
__cpufreq_driver_target(...) ??

There are few problems here:
- If we simply call above routine with X, then it will simply return as
X == policy->cur. And I don't want to hack this code in a bad way now :)

- So, probably the way it is implemented is right, as we do that the most
efficient way. We just broadcast the new freq in case there is a difference
otherwise nothing.
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