linux-kernel - Re: [PATCH v7 4/4] thermal: mediatek: add another get

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Date:   Wed, 25 Jan 2023 11:02:03 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Amjad Ouled-Ameur <aouledameur@...libre.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Amit Kucheria <amitk@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>
Cc:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Fabien Parent <fparent@...libre.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Markus Schneider-Pargmann <msp@...libre.com>,
        linux-pm@...r.kernel.org, Rob Herring <robh@...nel.org>,
        Michael Kao <michael.kao@...iatek.com>,
        linux-kernel@...r.kernel.org, Hsin-Yi Wang <hsinyi@...omium.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v7 4/4] thermal: mediatek: add another get_temp ops for
 thermal sensors

On 24/01/2023 23:27, Amjad Ouled-Ameur wrote:
> 
> On 1/24/23 18:55, Daniel Lezcano wrote:
>> On 24/01/2023 18:46, Amjad Ouled-Ameur wrote:
>>>
>>> On 1/24/23 17:54, Daniel Lezcano wrote:
>>>>
>>>> Hi Amjad,
>>>>
>>>> On 24/01/2023 11:08, Amjad Ouled-Ameur wrote:
>>>>
>>>> [ ... ]
>>>>
>>>>>>>
>>>>>>> IIUC, there is a sensor per couple of cores. 1 x 2Bigs, 1 x 
>>>>>>> 2Bigs, 1 x 4 Little, right ?
>>>>>>
>>>>>> MT8365 SoC has 4 x A53 CPUs. The SoC has 4 thermal zones per 
>>>>>> sensor. Thermal zone 0 corresponds
>>>>>>
>>>>>> to all 4 x A53 CPUs, the other thermal zones (1, 2 and 3) has 
>>>>>> nothing to do with CPUs. The cooling device type
>>>>>>
>>>>>> used for CPUs is passive. FYI, thermal zones 1, 2 and 3 are 
>>>>>> present in the SoC for debug-purpose only, they are not supposed
>>>>>>
>>>>>> to be used for production.
>>>>>>
>>>>> After reconsidering the fact that zones 1, 2 and 3 are only used 
>>>>> for dev/debug, it might be best to avo >
>>>>> aggregation as you suggested, and keep only support for zone 0 in 
>>>>> this driver. Thus I suggest I send a V8
>>>>>
>>>>> where I keep only below fixes for this patch if that's okay with you:
>>>>>
>>>>> - Define "raw_to_mcelsius" function pointer for "struct 
>>>>> thermal_bank_cfg".
>>>>>
>>>>> - Fix "mtk_thermal" variable in mtk_read_temp().
>>>>>
>>>>> - Set "mt->raw_to_mcelsius" in probe().
>>>>>
>>>>>
>>>>> For zones 1, 2 and 3 we can later add a different driver specific 
>>>>> for dev/debug to probe them to
>>>>>
>>>>> avoid confusion.
>>>>
>>>> You can add them in the driver and in the device tree, but just add 
>>>> the cooling device for the thermal zone 0.
>>>
>>> Thermal zone 0 uses CPU{0..3} for passive cooling, in this case we 
>>> should register cooling device with
>>>
>>> cpufreq_cooling_register() for each CPU right ?
>>
>> No, the OF code device tree does already that. You just have to 
>> register the different thermal zones.
>>
>> Do you have a pointer to a device tree for this board and the thermal 
>> setup ?
> 
> Sure, here is a dtsi for MT8365 SoC which contains thermal nodes [0].

 From my POV, there are two different setup with the DT but only one 
implementation with the driver.

The driver should register all the thermal zones for each CPUs. For 
that, make things nice with the defines for the dt-bindings like [1].

Then the device tree:

setup1:

Describe all the thermal zones in the DT which will be similar to [2]. 
Each CPU has a thermal zone, trip points and the same cooling device.

The first thermal zone reaching the trip temperature threshold will 
start the mitigation. The thermal framework takes care of multiple 
thermal zones sharing the same cooling device.

The result will be the same as the max temperature aggregation you did 
previously.

setup2:

Describe all the thermal zones in the DT [3], but add the cooling device 
only on the sensor you are interested in mitigating.


And finally, if the sensors should be used to describe a kind of 
temperature gradient, a linear equation could be used but that is not 
implemented yet in the thermal framework.

Hope that helps

   -- Daniel

[1] 
https://lore.kernel.org/linux-arm-kernel/5dd5c795-5e67-146d-7132-30fc90171d4c@collabora.com/T/#Z2e.:..:20230124131717.128660-3-bchihi::40baylibre.com:1include:dt-bindings:thermal:mediatek-lvts.h

[2] 
https://lore.kernel.org/linux-arm-kernel/5dd5c795-5e67-146d-7132-30fc90171d4c@collabora.com/T/#m303240c4da71f6f37831e5d1b6f3da771ae8dd90

[3] 
https://lore.kernel.org/linux-arm-kernel/5dd5c795-5e67-146d-7132-30fc90171d4c@collabora.com/T/#Z2e.:..:20230124131717.128660-6-bchihi::40baylibre.com:1arch:arm64:boot:dts:mediatek:mt8195.dtsi


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