linux-kernel - Re: [PATCH v1 03/10] ARM: tegra: acer-a500: Bump thermal trips by 10C

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Date:   Fri, 11 Jun 2021 11:52:59 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Agneli <poczt@...tonmail.ch>, Paul Fertser <fercerpav@...il.com>,
        Svyatoslav Ryhel <clamor95@...il.com>,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 03/10] ARM: tegra: acer-a500: Bump thermal trips by 10C

On 14/05/2021 23:16, Michał Mirosław wrote:
> On Mon, May 10, 2021 at 11:25:53PM +0300, Dmitry Osipenko wrote:
>> It's possible to hit the temperature of the thermal zone in a very warm
>> environment under a constant load, like watching a video using software
>> decoding. It's even easier to hit the limit with a slightly overclocked
>> CPU. Bump the temperature limit by 10C in order to improve user
>> experience. Acer A500 has a large board and 10" display panel which are
>> used for the heat dissipation, the SoC is placed far away from battery,
>> hence we can safely bump the temperature limit.
> 
> 60^C looks like a touch-safety limit (to avoid burns for users). Did you
> verify the touchable parts' temperature somehow after the change?

The skin temperature and the CPU/GPU etc ... temperatures are different
things.

For the embedded system there is the dissipation system and a
temperature sensor on it which is the skin temp. This temperature is the
result of the heat of all the thermal zones on the board and must be
below 45°C. The temperature slowly changes.

On the CPU, the temperature changes can be very fast and you have to
take care of keeping it below the max temperature specified in the TRM
by using different techniques (freq changes, idle injection, ...) but
the temperature can be 75°C, 85°C or whatever the manual says.

50°C and 60°C are low temperature for a CPU and that will inevitably
impact the performances, so setting the temperature close the max
temperature is what will allow max performances.

What matters is the skin temperature.

The skin temperature must be monitored by other techniques, eg. using
the TDP of the system and throttle the different devices to keep them in
this power budget. That is the role of an thermal daemon.

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