linux-kernel - Re: Thermal driver with safeguards

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Message-ID: <3fbab873-c11f-40f7-b3eb-fa3c18528ba2@tuxedocomputers.com>
Date: Fri, 10 Jan 2025 17:56:18 +0100
From: Werner Sembach <wse@...edocomputers.com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>,
 "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
 "Rafael J . Wysocki" <rafael@...nel.org>
Cc: rui.zhang@...el.com, Hans de Goede <hdegoede@...hat.com>,
 Armin Wolf <W_Armin@....de>, Ilpo Järvinen
 <ilpo.jarvinen@...ux.intel.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 platform-driver-x86@...r.kernel.org
Subject: Re: Thermal driver with safeguards

Hi Daniel,

Am 09.01.25 um 22:36 schrieb Daniel Lezcano:
> On 02/12/2024 15:52, Werner Sembach wrote:
>> Hi,
>>
>> given a pair of a temperature sensor and a fan, I want to implement a driver. 
>> that allows userspace to directly control the fan if it wants to. But have a 
>> minimum fan speed when certain high temperatures are reached to avoid crashes 
>> or hardware damage.
>
> From the userspace, use directly the thermal-engine which is currently under 
> development [1]. You can add your platform specific code in a plugin while the 
> thermal engine will catch all the thermal events and pass them to it [2].
>
> The thermal engine has a configuration file which will setup the thermal 
> framework to be woken up at different temperatures.
That still requires to trust userspace/the user to not write dangerous values 
directly to sysfs?
>
> The thermal engine will be proposed for a distro package, so the platform 
> support will be automatically supported.
>
> Beside the trip points can be setup in the device to act on higher temperature.
As far as i can tell these trip points only notify userspace but you can't 
attach code executed in kernel to it.
>
> What is unclear is how the fan is managed. I suggest to have a look at 
> pwm-fan.c in drivers/hwmon

I already looked at hwmon, but that basically just writes trough values from and 
to userspace and has no kernel side management of temperatures and fan speeds 
whatsoever.

Kind regards,

Werner

>
>> e.g.
>>
>> - temperature of target die is 80°C -> fan speed must be at least 30%
>>
>> - temperature of target die is 90°C -> fan speed must be at least 40%
>>
>> - temperature of target die is 105°C -> fan speed must be 100%
>>
>> - temperature of target die is 110°C -> device shuts off to protect the hardware
>>
>> Would the thermal subsystem be the right place for this to implement this 
>> protection in driver?
>>
>> It already has functions around periodic temperature polling and trip points.
>
> [1] https://github.com/Linaro/libpm/tree/master
> [2] 
> https://github.com/Linaro/libpm/blob/master/thermal-engine/plugins/te-plugin-example-game.c
>
>