linux-kernel - Re: [PATCH v2 4/7] cpufreq: report whether cpufreq supports Frequency Invariance (FI)

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Date:   Tue, 4 Aug 2020 12:16:56 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ionela Voinescu <ionela.voinescu@....com>
Cc:     rjw@...ysocki.net, dietmar.eggemann@....com,
        catalin.marinas@....com, sudeep.holla@....com, will@...nel.org,
        linux@...linux.org.uk, mingo@...hat.com, peterz@...radead.org,
        linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/7] cpufreq: report whether cpufreq supports
 Frequency Invariance (FI)

On 03-08-20, 16:24, Ionela Voinescu wrote:
> Right, cpufreq_register_driver() should check that at least one of them
> is present

> (although currently cpufreq_register_driver() will return
> -EINVAL if .fast_switch() alone is present - something to be fixed).

I think it is fine as there is no guarantee from cpufreq core if
.fast_switch() will get called and so target/target_index must be
present. We can't do fast-switch today without schedutil (as only that
enables it) and if a notifier gets registered before the driver, then
we are gone again.

> Will do, on both accounts.
> 
> 
> > > +		static_branch_enable_cpuslocked(&cpufreq_set_freq_scale);
> > > +		pr_debug("%s: Driver %s can provide frequency invariance.",
> > > +			 __func__, driver->name);
> > 
> > I think a simpler print will work well too.
> > 
> >                 pr_debug("Freq invariance enabled");
> > 
> 
> I think the right way of reporting this support is important here.

Yeah, we can't say it is enabled as you explained, though I meant
something else here then, i.e. getting rid of driver name and
unimportant stuff. What about this now:

pr_debug("supports frequency invariance");

This shall get printed as this finally:

cpufreq: supports frequency invariance

-- 
viresh