linux-kernel - Re: [PATCH v3 1/3] cpufreq: add cpufreq_driver_resolve

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Message-ID: <20160721232131.GS27987@graphite.smuckle.net>
Date:	Thu, 21 Jul 2016 16:21:31 -0700
From:	Steve Muckle <steve.muckle@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Steve Muckle <steve.muckle@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	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 v3 1/3] cpufreq: add cpufreq_driver_resolve_freq()

On Thu, Jul 21, 2016 at 01:30:41PM -0700, Viresh Kumar wrote:
> Okay, but in that case shouldn't we do something like this:
> 
> unsigned int cpufreq_driver_resolve_freq(struct cpufreq_policy *policy,
>                                         unsigned int target_freq)
> {
>        target_freq = clamp_val(target_freq, policy->min, policy->max);
>        policy->cached_target_freq = target_freq;
> 
>        if (cpufreq_driver->target_index) {
>        		policy->cached_resolved_idx =
>        		        cpufreq_frequency_table_target(policy, target_freq,
>        		                                       CPUFREQ_RELATION_L);
>        		return policy->freq_table[policy->cached_resolved_idx].frequency;
>        }
> 
>        if (cpufreq_driver->resolve_freq)
>                return cpufreq_driver->resolve_freq(policy, target_freq);
> }

Thanks for the review.

My thinking (noted in the commit text) was that the caller of
cpufreq_driver_resolve_freq() would verify that the driver supported the
proper calls before using this API. This way it can be checked once,
presumably in a governor's init routine. Checking the pointer over and
over again in a fast path is wasteful.