linux-kernel - Re: [PATCH v3] arm64: dts: rockchip: add thermal fan control to rockpro64

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Date:   Fri, 13 Aug 2021 16:54:42 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Robin Murphy <robin.murphy@....com>,
        Peter Geis <pgwipeout@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>
Cc:     devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] arm64: dts: rockchip: add thermal fan control to
 rockpro64


Hi Robin,


On 13/08/2021 15:51, Robin Murphy wrote:
> On 2021-08-13 13:59, Daniel Lezcano wrote:
>> On 30/07/2021 17:17, Peter Geis wrote:
>>> The rockpro64 had a fan node since
>>> commit 5882d65c1691 ("arm64: dts: rockchip: Add PWM fan for RockPro64")
>>> however it was never tied into the thermal driver for automatic control.
>>>
>>> Add the links to the thermal node to permit the kernel to handle this
>>> automatically.
>>> Borrowed from the (rk3399-khadas-edge.dtsi).
>>>
>>> Signed-off-by: Peter Geis <pgwipeout@...il.com>

[ ... ]

>>>   +&cpu_thermal {
>>> +    trips {
>>> +        cpu_warm: cpu_warm {
>>> +            temperature = <55000>;
>>> +            hysteresis = <2000>;
>>> +            type = "active";
>>> +        };
>>> +
>>> +        cpu_hot: cpu_hot {
>>> +            temperature = <65000>;
>>> +            hysteresis = <2000>;
>>> +            type = "active";
>>> +        };
>>> +    };
>>> +
>>
>> Why two trip points ?
>>
>> Why not one functioning temperature and no lower / upper limits for the
>> cooling maps ?
> 
> Certainly when I first did this for NanoPC-T4, IIRC it was to avoid the
> fan ramping up too eagerly, since level 1 for my fan is effectively
> silent but still cools enough to let a moderate load eventually settle
> to a steady state below the second trip.

Thanks for your answer.

What would be the governor for this setup ?




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