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

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Date:   Fri, 28 Jul 2017 20:43:22 -0700
From:   Joel Fernandes <joelaf@...gle.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
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 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? 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?

thanks,

-Joel