linux-kernel - Re: [PATCH v6 3/5] thermal: renesas: rzg3e: Add thermal driver for the Renesas RZ/G3E SoC

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Message-ID: <6e496737-3cec-425e-a4a1-29b576f8eade@linaro.org>
Date: Tue, 5 Aug 2025 12:05:45 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: John Madieu <john.madieu.xa@...renesas.com>
Cc: "conor+dt@...nel.org" <conor+dt@...nel.org>,
 "geert+renesas@...der.be" <geert+renesas@...der.be>,
 "krzk+dt@...nel.org" <krzk+dt@...nel.org>,
 "rafael@...nel.org" <rafael@...nel.org>,
 Biju Das <biju.das.jz@...renesas.com>,
 "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
 "john.madieu@...il.com" <john.madieu@...il.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
 "linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>,
 "lukasz.luba@....com" <lukasz.luba@....com>,
 "magnus.damm" <magnus.damm@...il.com>, "robh@...nel.org" <robh@...nel.org>,
 "rui.zhang@...el.com" <rui.zhang@...el.com>,
 "sboyd@...nel.org" <sboyd@...nel.org>,
 "niklas.soderlund+renesas@...natech.se"
 <niklas.soderlund+renesas@...natech.se>
Subject: Re: [PATCH v6 3/5] thermal: renesas: rzg3e: Add thermal driver for
 the Renesas RZ/G3E SoC


Hi John,


On 05/08/2025 09:49, John Madieu wrote:

[ ... ]

>>> I might not get what you are asking, but since I compute the
>>> temperature in the hard IRQ handler, I just wait for it to complete
>>> and notify the completion so I can grab the processed value to notify
>>> the thermal core.
>>>
>>> Please let me know if this does not answer your question.
>>
>> Can you describe how the sensor works ? And perhaps if you have a pointer
>> to some documentation ?
> 
> Here is the documentation [1]. The thermal device is referred to as TSU.
> 
> [1] https://www.renesas.com/en/document/mah/rzg3e-group-users-manual-hardware?r=25574493
> 
>>    [ ... ]

Thanks for the pointer. I got it now ;)

I'm a bit worried about the latency introduced by this mechanism when 
the system is entering in a thermal pressure episode.

The get_temp function wait for a completion up to 100ms, it is a lot. 
Especially if the userspace can be reading the temperature and blocking 
the read.

There is also the spin_lock taken introducing another lock while the 
get_temp function is holding a mutex on the thermal zone.

Did you it that under stress ?

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