linux-kernel - Re: [PATCH v2 3/3] thermal: cpu_cooling: Migrate to using the EM framework

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Message-ID: <20190423080732.rmwxjh67re57sayk@queper01-lin>
Date:   Tue, 23 Apr 2019 09:07:35 +0100
From:   Quentin Perret <quentin.perret@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
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,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, mka@...omium.org
Subject: Re: [PATCH v2 3/3] thermal: cpu_cooling: Migrate to using the EM
 framework

On Monday 22 Apr 2019 at 13:55:18 (+0530), Viresh Kumar wrote:
> On 18-04-19, 09:04, Quentin Perret wrote:
> > On Thursday 18 Apr 2019 at 09:23:23 (+0530), Viresh Kumar wrote:
> > > On 17-04-19, 10:43, Quentin Perret wrote:
> > > >  static struct thermal_cooling_device *
> > > >  __cpufreq_cooling_register(struct device_node *np,
> > > > -			struct cpufreq_policy *policy, u32 capacitance)
> > > > +			struct cpufreq_policy *policy,
> > > > +			struct em_perf_domain *em)
> > > >  {
> > > 
> > > > +	if (em_is_sane(cpufreq_cdev, em)) {
> > > > +		cpufreq_cdev->em = em;
> > > >  		cooling_ops = &cpufreq_power_cooling_ops;
> > > > -	} else {
> > > > +	} else if (policy->freq_table_sorted != CPUFREQ_TABLE_UNSORTED) {
> > > >  		cooling_ops = &cpufreq_cooling_ops;
> > > > +	} else {
> > > > +		WARN(1, "cpu_cooling: no valid frequency table found\n");
> > > 
> > > Well the frequency table is valid, isn't it ?
> > 
> > True ...
> > 
> > > Maybe something like: "cpu_cooling doesn't support unsorted frequency tables" ?
> > 
> > Right, otherwise I guess that could be confused with the check on
> > cpu_table_count_valid_entries() above. And while I'm thinking about it
> > perhaps WARN is a bit too much here ? We can handle the error safely so
> > pr_err() should be enough ?
> 
> Hmm, I would keep the WARN as it is hard to miss it compared to a
> simple pr_err.

Right, I don't really mind either way TBH. But is this worse than having
a NULL policy for example ? We have a standard pr_err() in this case.
And same thing if the cooling device registration failed actually. Do
you see a good reason to deal with EM stuff differently ?

Thanks,
Quentin