linux-kernel - Re: [PATCH V2] cpufreq: Disallow ->resolve_freq() for drivers providing ->target

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Message-ID: <20160722151327.GP3122@ubuntu>
Date:	Fri, 22 Jul 2016 08:13:27 -0700
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Steve Muckle <steve.muckle@...aro.org>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Linux PM <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Juri Lelli <Juri.Lelli@....com>,
	Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH V2] cpufreq: Disallow ->resolve_freq() for drivers
 providing ->target_index()

On 21-07-16, 17:34, Steve Muckle wrote:
> On Fri, Jul 22, 2016 at 02:18:54AM +0200, Rafael J. Wysocki wrote:
> > > My thinking was that one of these two would be preferable:
> > >
> > > - Forcing ->target() drivers to install a ->resolve_freq callback,
> > >   enforcing this at cpufreq driver init time.
> > 
> > That would have been possible, but your series didn't do that.
> > 
> > >   My understanding is
> > >   ->target() drivers are deprecated anyway
> > 
> > No, they aren't.
> 
> Ok. I didn't follow Documentation/cpu-freq/cpu-drivers.txt section 1.5
> then - it suggests something about target() is deprecated, perhaps it's
> out of date.

They are kind of deprecated for the new uesrs, but we still have
handful of users of it.

> Sorry, that should've been "check that either ->target_index() or
> ->resolve_freq() is implemented." 
> 
> Implementing resolve_freq for the target() drivers and requiring it at
> driver init time is probably the better way to go though. Perhaps I can
> work on this at some point.

As I said earlier as well in one of the emails, if you are worried
about the extra 'if' check in the hot path, then wouldn't this fix it
for you?

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 3dd4884c6f9e..91d8ec4c8eb7 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -517,7 +517,7 @@ unsigned int cpufreq_driver_resolve_freq(struct cpufreq_policy *policy,
                return policy->freq_table[idx].frequency;
        }
 
-       if (cpufreq_driver->resolve_freq)
+       if (likely(cpufreq_driver->resolve_freq))
                return cpufreq_driver->resolve_freq(policy, target_freq);
 
        return target_freq;

-- 
viresh