linux-kernel - Re: [PATCH V5 2/2] cpufreq: Process remote callbacks from any CPU if the platform permits

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Date:   Mon, 31 Jul 2017 09:30:07 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steve Muckle <smuckle.linux@...il.com>,
        Juri Lelli <juri.lelli@....com>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        eas-dev@...ts.linaro.org, Saravana Kannan <skannan@...eaurora.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V5 2/2] cpufreq: Process remote callbacks from any CPU if
 the platform permits

On 28-07-17, 20:43, Joel Fernandes wrote:
> On Thu, Jul 27, 2017 at 11:46 PM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > On many platforms, CPUs can do DVFS across cpufreq policies. i.e CPU
> > from policy-A can change frequency of CPUs belonging to policy-B.
> >
> > This is quite common in case of ARM platforms where we don't
> > configure any per-cpu register.
> >
> > Add a flag to identify such platforms and update
> > cpufreq_can_do_remote_dvfs() to allow remote callbacks if this flag is
> > set.
> >
> > Also enable the flag for cpufreq-dt driver which is used only on ARM
> > platforms currently.
> >
> > Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> > ---
> >  drivers/cpufreq/cpufreq-dt.c |  1 +
> >  include/linux/cpufreq.h      | 18 ++++++++++++++++--
> >  2 files changed, 17 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
> > index fef3c2160691..d83ab94d041a 100644
> > --- a/drivers/cpufreq/cpufreq-dt.c
> > +++ b/drivers/cpufreq/cpufreq-dt.c
> > @@ -274,6 +274,7 @@ static int cpufreq_init(struct cpufreq_policy *policy)
> >                 transition_latency = CPUFREQ_ETERNAL;
> >
> >         policy->cpuinfo.transition_latency = transition_latency;
> > +       policy->dvfs_possible_from_any_cpu = true;
> >
> 
> Are there also ARM hardware that may not support it?

I don't think so. ARM never had any per-cpu register interface which may break
due to this.

> If yes, wouldn't
> a saner thing to do be to keep default as false and read the property
> from DT for hardware that does support it and then set to true?

I would do it if required, but for now I don't think there are any such users of
cpufreq-dt.

-- 
viresh