linux-kernel - Re: [PATCH 0/2] Add exit_prepare callback to the cpufreq

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Date:	Thu, 4 Sep 2014 11:38:59 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Dirk Brandewie <dirk.brandewie@...il.com>,
	Dirk Brandewie <dirk.j.brandewie@...el.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Patrick Marlier <patrick.marlier@...il.com>
Subject: Re: [PATCH 0/2] Add exit_prepare callback to the cpufreq_driver interface.

On 19 March 2014 19:49, Rafael J. Wysocki <rjw@...ysocki.net> wrote:

> That said, for the intel_pstate case ->stop() as proposed by Dirk is demonstrably
> sufficient and there are no other ->setpolicy drivers in sight wanting or needing
> anything else.
>
> So to me, (1) the new ->stop() should *only* be called for ->setpolicy drivers,
> because the purpose of it should be to "allow ->setpolicy drivers to do what the
> GOV_STOP will do for regular drivers" as you put it above, and (2) some code in
> the original intel_pstate's ->exit() may/should stay in there (instead of being
> moved to the new ->stop()), which is the only possibly remaining issue here.
>
> The whole discussion about possibly re-using ->stop() for ->target drivers goes
> in a totally wrong direction, because *if* ->target drivers need a new callback
> to be executed around where ->stop() is called for ->setpolicy drivers, *then*
> that has to be a *different* callback.
>
> And by the way, ->get() in fact has a different meaning for ->setpolicy drivers,
> so it would be good to consider logical separation of ->setpolicy and ->target
> drivers so that each kind has its own separate set of callbacks with no overlaps.
> That would make it easier to avoid breakage resulting from changes made with
> ->setpolicy drivers that also affect ->target drivers in unpredictable ways and
> the other way around.

Okay, I have picked up a very old thread but it looks more sensible to start
replying here..

Preeti (Cc'd) wants to do something similar, i.e. reduce freq of a
core before it
goes down. And the driver is probably: drivers/cpufreq/powernv-cpufreq.c, which
is ->target() type.

Now should we reuse the same callback ->stop_cpu() or implement a new one?
I don't know if adding a new callback would be a good idea here..

--
viresh
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