linux-kernel - Re: [PATCH v2 47/48] ARM: tegra: ventana: Support CPU voltage scaling and thermal throttling

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Message-ID: <ce603c74-3a20-7331-36a7-d7bc43ce36b6@gmail.com>
Date:   Thu, 17 Dec 2020 23:28:56 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Peter Geis <pgwipeout@...il.com>,
        Nicolas Chauvet <kwizart@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-media@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH v2 47/48] ARM: tegra: ventana: Support CPU voltage scaling
 and thermal throttling

17.12.2020 22:36, Daniel Lezcano пишет:
>>>> +					type = "critical";
>>>> +				};
>>>> +			};
>>>> +
>>>> +			cooling-maps {
>>>> +				map0 {
>>>> +					trip = <&trip0>;
>>>> +					cooling-device = <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
>>> You should add all CPUs here.
>>
>> All CPU cores are coupled on Tegra in regards to CPUFreq, hence I think
>> it won't make any difference if secondary CPU cores will be added here,
>> isn't it?
> The explanation is in the description of commit ef4734500407ce4d

I think that really only makes sense if CPU cores have independent clock
rate management. IIRC, I actually made some research about this in the
past and intentionally removed the secondary cores from the
cooling-device since they didn't make any difference for a coupled CPU
cores.

That commit also says:

"But as soon as this CPU ordering changes and any other CPU is used to
bring up the cooling device, we will start seeing failures."

I don't quite understand to what "failures" that commit referrers. I
tried to change the cpu0 to cpu1 in the cooling-device and don't see any
failures. Could you please clarify this?

In general it should be fine to add all the cores to the cooling-device
and I'll do it in v3, but I want to make it clear why this is needed.