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

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Message-ID: <98ddf1b6-1804-4116-b4e2-f54a62c27966@tuxon.dev>
Date: Thu, 30 Jan 2025 22:53:22 +0200
From: Claudiu Beznea <claudiu.beznea@...on.dev>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: rafael@...nel.org, rui.zhang@...el.com, lukasz.luba@....com,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 geert+renesas@...der.be, magnus.damm@...il.com, mturquette@...libre.com,
 sboyd@...nel.org, p.zabel@...gutronix.de, ulf.hansson@...aro.org,
 linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH 2/6] thermal: of: Export non-devres helper to
 register/unregister thermal zone

Hi, Daniel,

On 30.01.2025 19:24, Daniel Lezcano wrote:
> On 30/01/2025 11:30, Claudiu Beznea wrote:
>>
>>
>> On 30.01.2025 12:07, Daniel Lezcano wrote:
>>> On Thu, Jan 30, 2025 at 11:08:03AM +0200, Claudiu Beznea wrote:
>>>> Hi, Daniel,
> 
> [ ... ]
> 
>>>>> 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.
>>>
>>> Without any testing capturing the temperatures and compare between the
>>> always-on
>>> and on/off, it is hard to say if it is true or not. Up to you to test
>>> that or
>>> not. If you think it is fine, then let's go with it.
>>
>> I tested it with and w/o the runtime PM and on/off support (so, everything
>> ON from the probe) and the reported temperature values were similar.
> 
> 
> Did you remove the roundup to 0.5°C ?

I did the testing as suggested and, this time, collected results and
compared side by side. I read the temperature for 10 minutes, 60 seconds
after the Linux prompt showed up. There is, indeed, a slight difference b/w
the 2 cases.

When the runtime PM doesn't touch the clocks on read the reported
temperature varies b/w 53-54 degrees while when the runtime PM
enables/disables the clocks a single read reported 55 degrees, the rest
reported 54 degrees.

I plotted the results side by side here:
https://i2.paste.pics/f07eaeddc2ccc3c6695fe5056b52f4a2.png?trs=0a0eaab99bb59ebcb10051eb298f437c7cd50c16437a87392aebc16cd9013e18&rand=vWXm2VTrbt

Please let me know how do you consider it.

Thank you,
Claudiu

> 
>