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

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Date:	Thu, 21 Jul 2016 22:31:18 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	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>,
	Steve Muckle <smuckle@...aro.org>
Subject: Re: [PATCH v3 1/3] cpufreq: add cpufreq_driver_resolve_freq()

On Thursday, July 21, 2016 12:59:26 PM Viresh Kumar wrote:
> On 13-07-16, 13:25, Steve Muckle wrote:
> > Cpufreq governors may need to know what a particular target frequency
> > maps to in the driver without necessarily wanting to set the frequency.
> > Support this operation via a new cpufreq API,
> > cpufreq_driver_resolve_freq(). This API returns the lowest driver
> > frequency equal or greater than the target frequency
> > (CPUFREQ_RELATION_L), subject to any policy (min/max) or driver
> > limitations. The mapping is also cached in the policy so that a
> > subsequent fast_switch operation can avoid repeating the same lookup.
> > 
> > The API will call a new cpufreq driver callback, resolve_freq(), if it
> > has been registered by the driver. Otherwise the frequency is resolved
> > via cpufreq_frequency_table_target(). Rather than require ->target()
> > style drivers to provide a resolve_freq() callback it is left to the
> > caller to ensure that the driver implements this callback if necessary
> > to use cpufreq_driver_resolve_freq().
> > 
> > Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > Signed-off-by: Steve Muckle <smuckle@...aro.org>
> > ---
> >  drivers/cpufreq/cpufreq.c | 25 +++++++++++++++++++++++++
> >  include/linux/cpufreq.h   | 16 ++++++++++++++++
> >  2 files changed, 41 insertions(+)
> > 
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 118b4f30a406..b696baeb249d 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -492,6 +492,29 @@ void cpufreq_disable_fast_switch(struct cpufreq_policy *policy)
> >  }
> >  EXPORT_SYMBOL_GPL(cpufreq_disable_fast_switch);
> >  
> > +/**
> > + * cpufreq_driver_resolve_freq - Map a target frequency to a driver-supported
> > + * one.
> > + * @target_freq: target frequency to resolve.
> > + *
> > + * The target to driver frequency mapping is cached in the policy.
> > + *
> > + * Return: Lowest driver-supported frequency greater than or equal to the
> > + * given target_freq, subject to policy (min/max) and driver limitations.
> > + */
> > +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->resolve_freq)
> > +		return cpufreq_driver->resolve_freq(policy, target_freq);
> 
> Any reason why we still have this call around ? I thought the whole
> attempt I made was to get rid of this :)
> 
> The core can do this pretty much now by itself, why do we still want
> this call?

In case some drivers that don't use frequency tables want to implemet
fast switching, for example.

> Also, your series doesn't add a user for it yet, so better drop it for
> now.

That's correct, but then it is not so much of a maintenance burden and I may
need it.

I'm going to apply the whole series.

Thanks,
Rafael