linux-kernel - Re: [PATCH v5 3/3] thermal: cpu_cooling: Migrate to using the EM framework

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Date:   Fri, 31 May 2019 08:58:54 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     edubezval@...il.com, rui.zhang@...el.com, javi.merino@...nel.org,
        amit.kachhap@...il.com, rjw@...ysocki.net, will.deacon@....com,
        catalin.marinas@....com, daniel.lezcano@...aro.org,
        dietmar.eggemann@....com, ionela.voinescu@....com,
        mka@...omium.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 3/3] thermal: cpu_cooling: Migrate to using the EM
 framework

On 30-05-19, 12:27, Quentin Perret wrote:
> On Thursday 30 May 2019 at 10:20:38 (+0100), Quentin Perret wrote:
> > The newly introduced Energy Model framework manages power cost tables in
> > a generic way. Moreover, it supports several types of models since the
> > tables can come from DT or firmware (through SCMI) for example. On the
> > other hand, the cpu_cooling subsystem manages its own power cost tables
> > using only DT data.
> > 
> > In order to avoid the duplication of data in the kernel, and in order to
> > enable IPA with EMs coming from more than just DT, remove the private
> > tables from cpu_cooling.c and migrate it to using the centralized EM
> > framework. Doing so should have no visible functional impact for
> > existing users of IPA since:
> > 
> >  - recent extenstions to the the PM_OPP infrastructure enable the
> >    registration of EMs in PM_EM using the DT property used by IPA;
> > 
> >  - the existing upstream cpufreq drivers marked with the
> >    'CPUFREQ_IS_COOLING_DEV' flag all use the aforementioned PM_OPP
> >    infrastructure, which means they all support PM_EM. The only two
> >    exceptions are qoriq-cpufreq which doesn't in fact use an EM and
> >    scmi-cpufreq which doesn't use DT for power costs.
> > 
> > For existing users of cpu_cooling, PM_EM tables will contain the exact
> > same power values that IPA used to compute on its own until now. The
> > only new dependency for them is to compile in CONFIG_ENERGY_MODEL.
> > 
> > The case where the thermal subsystem is used without an Energy Model
> > (cpufreq_cooling_ops) is handled by looking directly at CPUFreq's
> > frequency table which is already a dependency for cpu_cooling.c anyway.
> > Since the thermal framework expects the cooling states in a particular
> > order, bail out whenever the CPUFreq table is unsorted, since that is
> > fairly uncommon in general, and there are currently no users of
> > cpu_cooling for this use-case.
> > 
> > Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> 
> Viresh: the patch hasn't changed much so I kept this, but please shout
> if you're not happy with the new version :-)

Yeah, it  looked fine and so I didn't complain :)

-- 
viresh