Re: [PATCH 2/6] thermal: of: Export non-devres helper to register/unregister thermal zone

Daniel Lezcano
2025-01-30T17:31:57Z

On 30/01/2025 11:33, Biju Das wrote:
> Hi Daniel Lezcano,
>
>> -----Original Message-----

[ ... ]

>>>> I've been through the driver before responding to this change. What
>>>> is the benefit of powering down / up (or clock off / on) the thermal
>>>> sensor when reading the temperature ?
>>>>
>>>> I can understand for disable / enable but I don't get for the
>>>> classic usage where a governor will be reading the temperature regularly.
>>>
>>> I tried to be as power saving as possible both at runtime and after
>>> the IP is not used anymore as the HW manual doesn't mentioned anything
>>> about accuracy or implications of disabling the IP clock at runtime.
>>> We use similar approach (of disabling clocks at runtime) for other IPs
>>> in the RZ/G3S SoC as well.
>>>
>>>>
>>>> Would the IP need some cycles to capture the temperature accurately
>>>> after the clock is enabled ?
>>>
>>> There is nothing about this mentioned about this in the HW manual of
>>> the RZ/G3S SoC. The only points mentioned are as described in the driver code:
>>> - wait at least 3us after each IIO channel read
>>> - wait at least 30us after enabling the sensor
>>> - wait at least 50us after setting OE bit in TSU_SM
>>>
>>> For this I chose to have it implemented as proposed.
>>
>> IMO, disabling/enabling the clock between two reads through the pm runtime may not be a good thing,
>> especially if the system enters a thermal situation where it has to mitigate.
>
> Just a question, You mean to avoid device destruction due to high temperature?? Assuming disabling the clk happens
> when the temp reaches the boundary and re-enabling of the clk after a time(which involves monitoring the CLK ON
> bit after enabling it, or a run time enable failure happens), where it exceeds the threshold??

Well, I have some comments with the device tree thermal configuration
which may answer your question but I'll wait for Claudiu to check the
temperature read comparison without rounding to 0.5°C

What I meant is if the temperature read is inaccurate, the mitigation
will be inaccurate too. It may not reach the critical temperature but it
is possible the performance could be impacted negatively under thermal
stress.

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