Patches were posted this week for implementing Microsoft's extensions around the ACPI fan device for allowing the operating system to set fan speed trip points. In turn this should help some HP systems and likely other OEMs too in getting fan information working under Linux.

Open-source developer Armin Wolf posted the patches this week for supporting Microsoft's _DSM interface for the ACPI fan device.

Armin explained with [1]the patch series :

"Microsoft has designed a _DSM interface for the ACPI fan device that allows the OS to set fan speed trip points. The ACPI firmware will notify the ACPI fan device when said trip points are triggered.

Unfortunately some device manufacturers (like HP) blindly assume that the OS will use this _DSM interface and thus only update the fan speed value returned by the _FST control method when sending a notification to the ACPI fan device. This results in stale fan speed values being reported by the ACPI fan driver."

With the patches for handling the Microsoft fan extensions, this should help different devices falling into that boat. The original [2]bug report last year was over missing fan information on an HP EliteBook 860.



[1] https://lore.kernel.org/linux-acpi/20251005222513.7794-1-W_Armin@gmx.de/

[2] https://github.com/lm-sensors/lm-sensors/issues/506