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

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Date:   Fri, 18 Dec 2020 00:56:14 +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

18.12.2020 00:19, Daniel Lezcano пишет:
> On 17/12/2020 21:28, Dmitry Osipenko wrote:
>> 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. 
> 
> ATM I did not see any ARM platform having a clock line per CPU but I may
> be wrong.
> 
>> 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.
> 
> AFAIR, if CPU0 is unplugged the cooling device can not rebind to CPU1.
> And if CPU0 is plugged in again, the cooling device fails to initialize.
> 
> And, if the CPUs are mapped with the physical CPU0 to Linux numbering
> CPU1, the cooling device mapping will fail.

Alright, thank you.