[Letux-kernel] [RFC] ARM: dts: omap36xx: Enable thermal throttling

Daniel Lezcano daniel.lezcano at linaro.org
Wed Sep 18 11:37:47 CEST 2019

On 18/09/2019 11:24, Viresh Kumar wrote:
> On 13-09-19, 00:33, Daniel Lezcano wrote:
>> Hi Adam,
>> On 12/09/2019 23:19, Adam Ford wrote:
>>> On Thu, Sep 12, 2019 at 4:12 PM Daniel Lezcano
>>> <daniel.lezcano at linaro.org> wrote:
>>>> On 12/09/2019 20:30, Adam Ford wrote:
>>>>> The thermal sensor in the omap3 family isn't accurate, but it's
>>>>> better than nothing.  The various OPP's enabled for the omap3630
>>>>> support up to OPP1G, however the datasheet for the DM3730 states
>>>>> that OPP130 and OPP1G are not available above TJ of 90C.
>>>>> This patch configures the thermal throttling to limit the
>>>>> operating points of the omap3630 to Only OPP50 and OPP100 if
>>>>> the thermal sensor reads a value above 90C.
>> Oh, that's a very interesting use case.
>> AFAICT the thermal framework is not designed to deal with this
>> situation. I agree this setup may work (even if I'm not convinced about
>> the stability of the whole).
>> May be Viresh can help for the cpufreq side?
> Sorry but I am not able to understand what's not supported by thermal framework
> here and what can I do to help :)

The solution of preventing running above the 90°C by changing the OPPs
is fine and works. It is a way of workaround the spec.

But AFAIU, the specs of the board say the OPPs 800MHz and 1GHz are only
permitted during an amount of time above 90°C which makes the constraint
inverted and recall somehow the 'turbo-mode' description:

- turbo-mode: Marks the OPP to be used only for turbo modes. Turbo mode
is available on some platforms, where the device can run over its
operating frequency for a short duration of time limited by the device's
power, current and thermal limits.

This is where I thought you can give an input.

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