linux-kernel - Re: [RFC PATCH v6 6/9] thermal: cpu_cooling: implement the power cooling device API

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Message-ID: <20141209103249.GB2891@e104805>
Date:	Tue, 9 Dec 2014 10:32:49 +0000
From:	"Javi Merino" <javi.merino@....com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Punit Agrawal <Punit.Agrawal@....com>,
	Mark Brown <broonie@...nel.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Eduardo Valentin <edubezval@...il.com>
Subject: Re: [RFC PATCH v6 6/9] thermal: cpu_cooling: implement the power
 cooling device API

Hi Viresh,

On Tue, Dec 09, 2014 at 01:59:39AM +0000, Viresh Kumar wrote:
> On 8 December 2014 at 19:52, Javi Merino <javi.merino@....com> wrote:
> > Ok, changed it into:
> >
> >         cpu = cpumask_any(&cpufreq_device->allowed_cpus);
> >         dev = get_cpu_device(cpu);
> >         if (!dev) {
> >                 dev_warn(&cpufreq_device->cool_dev->device,
> >                         "No cpu device for cpu %d\n", cpu);
> >                 ret = -EINVAL;
> >                 goto unlock;
> >         }
> >
> >         num_opps = dev_pm_opp_get_opp_count(dev);
> >         if (num_opps <= 0) {
> >                 ret = (num_opps < 0)? num_opps : -EINVAL;
> >                 goto unlock;
> >         }
> 
> And this might not work. This is what I said in the first reply.
> 
> So, a bit lengthy reply now :)
> 
> Every cpu has a device struct associated with it. When cpufreq
> core initializes drivers, they ask for mapping (initializing) the opps.
> At that point we pass policy->cpu to opp core. OPP core doesn't
> know which cores share clock line (I am trying to solve that [1]) and
> so it just initializes the OPPs for policy->cpu. Let us say it cpuX.
> 
> Now there will be few more CPUs which are going to share clock
> line with it and hence will use the same OPPs. In thermal core,
> you got clip_cpus which is exactly the masks of all these CPUs
> sharing clock line.
> 
> If the OPP layer is good enough, then above code can work. But
> because right now the OPPs are mapped to just cpuX, passing
> any other cpu from clip_cpus will fail as it doesn't have any associated
> OPPs.
> 
> Now what I asked you is to use the CPU for which
> __cpufreq_cooling_register() is called. Normally we are calling
> __cpufreq_cooling_register() for the CPU for which OPPs are
> registered (but people might call it up for other CPUs as well)..

Sorry but I don't follow.  __cpufreq_cooling_register() is passed a
clip_cpus mask, not a single cpu.  How do I get "the cpu for which
__cpufreq_cooling_register() is called" if not by looping through all
the cpus in the mask?
 
> So, using that cpu *might* have worked here.
> 
> Now the earlier loop you used was good to get this information,
> but it wasn't consistent and so I objected.
> 
> What you should do:
> 
> - Create another routine to find the cpu for which OPPs are bound
> to
> -  And save the cpu_dev for it in the global struct for cpu_cooling

This I have done, it wasn't part of the snip that I sent.

> - reuse it wherever required.

Same as above.

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