Re: acpithinkpad(4): no writable fan control on ThinkPad T490 (FreeBSD acpi_ibm can write it)

Thanks, and sorry for the off-list reply - adding [email protected] to CC no=
w and validating the challenge.

I checked hw.perfpolicy: it was already set to auto,auto here, so that is n=
ot the cause. At normal warm idle the fan sits at 3978 RPM with the thermal=
 zone at 51 C - calm thermals, nothing demanding running. So the EC fan cur=
ve is running hard regardless of perf policy.

The core gap is unchanged: acpithinkpad(4) exposes the fan only as a read-o=
nly sensor, so there is no interface to step it down. The same T490 runs qu=
iet under FreeBSD 14.4 and 15, where acpi_ibm(4) writes the fan level via t=
he EC HFSP register - so the hardware supports a write path that acpithinkp=
ad does not implement.

That is really the question: whether writable fan-level control in acpithin=
kpad(4) is feasible. Happy to test patches or run diagnostics on this exact=
 machine.

Thanks again for the help getting this onto the list properly.




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On Friday, June 26th, 2026 at 10:30, stephane Tranchemer <[email protected]>=
 wrote:

> Hello,
>=20
> you sent your answer to me only, include [email protected] in CC, then
> validate the challenge, if you want others on the mailing list to see it
> too :)
>