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    SubjectRe: [PATCH 8/8] thermal/drivers/cpu_cooling: Add the combo cpu cooling device
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    On 02/02/2018 11:42, Viresh Kumar wrote:
    > Hi Daniel,

    Hi Viresh,


    > I have gone through the other review comments, specially from Daniel T.. While I
    > share some of his concerns, I have few more of mine.
    >
    > On 23-01-18, 16:34, Daniel Lezcano wrote:
    >> +late_initcall(cpu_cooling_init);
    >
    > For example, this thing isn't going to fly nicely as you have assumed cpufreq
    > and cpuidle drivers are going to be part of the kernel itself. What if they are
    > modules and are inserted after late-init ? There are more cases like this where
    > the cpufreq driver may unregister the cpufreq cooling device on the fly and then
    > add it back. And so this stuff is a bit tricky.

    The cpuidle driver can not be compiled as a module.

    Agree the cpufreq driver can be unloaded and this part needs some
    adjustments.

    > Here is how I see the whole thing now:
    >
    > - Yes we need individual support for both cpufreq and cpuidle cooling devices,
    > and no one disagrees on that I believe.
    >
    > - There is nothing in the thermal framework that disallows both cpufreq and
    > cpuidle cooling devices to co-exist. Both would be part of the same thermal
    > zone and so will get throttled with the same thermal sensor event. And so we
    > will end up trying to cool down the SoC using both cpufreq and cpuidle
    > technique.

    No. It does not work because we will need different state for each
    cooling device and we need some logic behind.

    > - Now I am just wondering if we really need the "combo" functionality or not.
    > Can we fine tune the DT cpu-cooling properties (existing ones) for a platform,
    > so that it automatically acts as a combo cooling device? I am not 100% sure
    > its gonna fly, but just wanted to make sure its not possible to work around
    > with and then only try the combo device thing.
    >
    > For example, suppose that with just cpufreq-cooling device we need to take the
    > CPU down to 1 GHz from 2 GHz if we cross temperature 'X'. What if we can change
    > this policy from DT and say the cpufreq-cooling device goes to 1.5 GHz and
    > cpuidle-cooling device takes us to idle for 'y' us, and the effect of
    > combination of these two is >= the effect of the 1 GHz for just the
    > cpufreq-cooling device.
    >
    > Is there any possibility of this to work ?

    It does not make sense. The combo does that automatically by computing
    the power equivalence more precisely.


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