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Subject: Re: [PATCH] arm64: dts: meson: vim3: reduce cpu thermal fan trigger
 temperature
To:     Daniel Lezcano <daniel.lezcano@linaro.org>,
        Nick Xie <xieqinick@gmail.com>
Cc:     robh+dt@kernel.org, khilman@baylibre.com, jbrunet@baylibre.com,
        martin.blumenstingl@googlemail.com, devicetree@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org,
        Nick <nick@khadas.com>, artem@khadas.com
References: <20210609012849.797576-1-xieqinick@gmail.com>
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 <ee3341d9-350e-a84d-6836-3401be679b2a@baylibre.com>
 <CAP4nuTUt1vQjVP=3_NYaeu+m47f78ru6-MgGBiAqLeU9fJAsNg@mail.gmail.com>
 <09c65310-9441-9b97-d9ae-4695f0dd16af@linaro.org>
From:   Neil Armstrong <narmstrong@baylibre.com>
Organization: Baylibre
Message-ID: <259e150c-f25a-86cf-1109-b7370b5d7c10@baylibre.com>
Date:   Mon, 14 Jun 2021 15:17:26 +0200
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Hi,
On 11/06/2021 09:45, Daniel Lezcano wrote:
> On 11/06/2021 09:30, Nick Xie wrote:
>> Hello Neil,
>>
>>
>> Neil Armstrong <narmstrong@baylibre.com> 于2021年6月11日周五 下午3:15写道：
>>>
>>> Hi,
>>>
>>> On 11/06/2021 08:54, Nick Xie wrote:
>>>> Hello Neil,
>>>>
>>>> The MCU FAN won't work until the temperature reach to 80 degree centigrade,
>>>> Do you think the temperature is too high?
>>>
>>> I think 80 is tool high, but I fear 50 is way too low, but if you think 50 is OK after you ran some tests, just add it to the commit log and it's ok for me.
>>
>> I think it is OK, we use it for a long time.
> 
> 50°C sounds like normal temperature with regular load. That means the
> fan will be switched on most of the time when the board is used.
> 
> And this change may be put in regard with the other trip points in the
> common DT. For instance, enable the fan when reaching 80°C but set the
> passive trip point to 75°C instead of 85°C.
> 
> All that depends on the hardware characteristics and TDP which are in
> the TRM normally.
> 

I don't think such data exist in the datasheet or other public document, but the vendor source tree
sets:
- passive: 75°C
- hot 85°C
- critical 110°C

we set upstream:
- passive: 85°C
- hot 95°C
- critical 110°C

so maybe we should lower the passive & hot trip points, then the FAN 80°C trip point would be ok now according to Daniel's explanation.

Neil