linux-kernel - Re: [PATCH v4] arm64: dts: mediatek: mt7986-bpi-r3: Change fan PWM value for mid speed

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Message-ID: <e6246af6-eadf-4bee-9e1c-c17adb86b496@collabora.com>
Date: Tue, 29 Jul 2025 12:13:58 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Mikhail Kshevetskiy <mikhail.kshevetskiy@...sys.eu>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Matthias Brugger
 <matthias.bgg@...il.com>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org,
 Frank Wunderlich <frank-w@...lic-files.de>
Subject: Re: [PATCH v4] arm64: dts: mediatek: mt7986-bpi-r3: Change fan PWM
 value for mid speed

Il 29/07/25 09:56, Mikhail Kshevetskiy ha scritto:
> Popular cheap PWM fans for this machine, like the ones coming in
> heatsink+fan combos will not work properly at the currently defined
> medium speed. Trying different pwm setting using a command
> 
>    echo $value > /sys/devices/platform/pwm-fan/hwmon/hwmon1/pwm1
> 
> I found:
> 
>    pwm1 value     fan rotation speed   cpu temperature     notes
>    -----------------------------------------------------------------
>      0            maximal              31.5 Celsius        too noisy
>     40            optimal              35.2 Celsius        no noise hearable
>     95            minimal
>     above 95      does not rotate      55.5 Celsius
>    -----------------------------------------------------------------
> 
> Thus only cpu-active-high and cpu-active-low modes are usable.
> I think this is wrong.
> 
> This patch fixes cpu-active-medium settings for bpi-r3 board.
> 
> I know, the patch is not ideal as it can break pwm fan for some users.
> Likely this is the only official mt7986-bpi-r3 heatsink+fan solution
> available on the market.
> 
> This patch may not be enough. Users may wants to tweak their thermal_zone0
> trip points, thus tuning fan rotation speed depending on cpu temperature.
> That can be done on the base of the following example:
> 
>    === example =========
>    # cpu temperature below 25 Celsius degrees, no rotation
>    echo 25000 > /sys/class/thermal/thermal_zone0/trip_point_4_temp
>    # cpu temperature in [25..32] Celsius degrees, normal rotation speed
>    echo 32000 > /sys/class/thermal/thermal_zone0/trip_point_3_temp
>    # cpu temperature above 50 Celsius degrees, max rotation speed
>    echo 50000 > /sys/class/thermal/thermal_zone0/trip_point_2_temp
>    =====================
> 
> Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@...sys.eu>
> Acked-by: Frank Wunderlich <frank-w@...lic-files.de>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>