[Bug 221430] nvidia_wmi_ec_backlight: brightness writes silently dropped on HP OMEN 16 (2025)

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=221430

--- Comment #8 from Hans de Goede (hansg@kernel.org) ---
(In reply to floquimaurice from comment #7)
> Hi Hans,
> 
> I added acpi_backlight=native nvidia_wmi_ec_backlight.force=1 (and
> nvidia.NVreg_EnableBacklightHandler=0) to my kernel command line.
> 
> Here are the folders that appeared in /sys/class/backlight/:
> 
>     intel_backlight (max_brightness: 192000)
> 
>     nvidia_0 (max_brightness: 100)
> 
>     nvidia_wmi_ec_backlight (max_brightness: 100)
> 
> I tried echoing different values into the brightness file for each of these
> three folders. The commands were accepted without any errors, but the
> physical screen brightness did not change at all.
> 
> I am just reporting the facts here. Let me know if you need me to run any
> other specific commands or tests!

Ok, so this is not a classic "which backlight driver should we use" problem.
But rather some issue with one of the backlight drivers.

The 192000 max-brightness for the intel_backlight looks suspicious.

Assuming that the LCD panel is indeed being driven by the Intel GPU and not
muxed to the nvidia GPU then I would start with filing a bug against the i915
driver:

https://drm.pages.freedesktop.org/intel-docs/how-to-file-i915-bugs.html

What value did you select in the BIOS for the hybrid-GPU config ? If you
selected discrete only instead of one of the hybrid options then this more
likely is an nvidia driver issue...

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