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

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Message-ID: <2699050.43LHVsRP52@vostro.rjw.lan>
Date:	Thu, 04 Sep 2014 21:56:12 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Preeti U Murthy <preeti@...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 Thursday, September 04, 2014 04:07:28 PM Viresh Kumar wrote:
> 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.

OK, if that works for everybody.  For one, I wouldn't like to end up with a
callback used for different things in every drvier implementing it.

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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