Re: [REGRESSION] thermal: per-zone hwmon names break Steam Deck fan control

Hi,

On Wed, Jul 29, 2026 at 10:50=E2=80=AFPM Matthew Schwartz
<[email protected]> wrote:
>
> Hello,
>
> After upgrading my Steam Deck OLED to a 7.2-rc kernel, the userspace fan =
control daemon that I use stopped working. I bisected the regression to d63=
23469bcfb ("thermal: hwmon: Register a hwmon device for each thermal zone")=
.
>
> Before this commit, the ACPI thermal-zone hwmon name was acpitz, while af=
ter the change it is now acpitz_0.
>
> The device profiles for fan control rely on the exact `acpitz` hwmon nami=
ng like the below code snippet:
>
> devices:
>   - hwmon_name: acpitz
>     nice_name: CPU
>     max_temp: 90
>     temp_hysteresis: 0
>     sensor_name: temp1
>
> So now, the profile fails to load with:
>
> fancontrol.py[40528]: Warning: hwmons not fully loaded, retrying...
> fancontrol.py[40528]: Warning: hwmons not fully loaded, retrying...
> fancontrol.py[40528]: Warning: hwmons not fully loaded, retrying...
> fancontrol.py[40528]: Traceback (most recent call last):
> fancontrol.py[40528]:   File "/usr/share/jupiter-fan-control/fancontrol.p=
y", line 606, in <module>
> fancontrol.py[40528]:     raise FileNotFoundError("Failed to load hwmons =
after 10 attempts.")
> fancontrol.py[40528]: FileNotFoundError: Failed to load hwmons after 10 a=
ttempts.
>
> Because initialization fails, the daemon never enters its fan-control loo=
p or writes the requested fan target.
>
> This change was also backported to Linux 7.1.5 as commit 996957016bc1, so=
 the regression is present there as well and has led to a userspace ABI reg=
ression. I can look at accommodating the change on the userspace side, but =
it still seemed worth reporting as a kernel regression.
>
> Thanks,
> Matt
>
> #regzbot introduced: d6323469bcfbda91f0aa89b7b39ad45fe822ca5d

Thanks for the report!

I think that commit d6323469bcfb will need to be reverted.