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

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Date:	Thu, 4 Sep 2014 16:07:28 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	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 4 September 2014 15:33, Preeti U Murthy <preeti@...ux.vnet.ibm.com> wrote:
> I think Rafael's point was that since no driver that had implemented the
> target_index callback was using it at the time that this patch was
> proposed, it was be best to couple the check on existence of stop_cpu
> callback with the the check on the kind of cpufreq driver. However
> powerpc is also in need of this today and we implement the target_index
> callback and find it convenient to use the stop CPU callback.

No, this is what he said..

"
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"
"

> Rafael, in which case would it not make sense to remove the check on
> driver->setpolicy above?
>
> Besides, I don't understand very well why we had this double check in
> the first place. Only if the drivers are in need of the functionality
> like stop_cpu, would they have implemented this callback right? If we
> are to assume that the drivers which have implemented the target_index
> callback should never be needing it, they would not have implemented the
> stop CPU callback either. So what was that, which was blatantly wrong
> with just having a check on stop_cpu? I did go through the discussion
> but did not find a convincing answer to this.

The idea was to get something similar to GOV_STOP for setpolicy drivers.
But in the end we didn't get to that. What we do in GOV_STOP is stop
changing CPUs frequency, but here in stop_cpu() we can stop changing
CPUs frequency OR take it to minimum, whatever we want..

As I said earlier, probably we should just do what you did in your patch +
some documentation changes.
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