Re: Regression: Backlight control broken on HP Omen 15‑ax246nf with kernel 7.0.0‑28‑generic

On Tue, Aug 18, 2026 at 3:03 PM harryblanc <[email protected]> wrote:
>
> *Subject:* Re: Regression: Backlight control broken on HP Omen
> 15‑ax246nf with kernel 7.0.x
>
> Hello Rafael, Thorsten,
>
> Here are the outputs you requested, from both the working kernel
> (6.17.0‑42) and the failing one (7.0.0‑29).
>
> For context:
>
>   *
>
>     Secure Boot is *disabled* on this machine.
>
>   *
>
>     GPU setup is *Optimus with NVIDIA GTX 1050 “on‑demand” mode* (Intel
>     iGPU is primary).
>
>   *
>
>     These changes do not affect the issue: the backlight regression
>     remains exactly the same on kernel 7.0.29.
>
>   *
>
>     Kernel 6.17.0‑42 (backlight working normally)
>
>   *
>
>     $ ls -l /sys/bus/acpi/drivers/video/
>     total 0
>     --w------- 1 root root 4096 août 18 14:50 bind
>     lrwxrwxrwx 1 root root    0 août 18 14:50 LNXVIDEO:00 ->
>     ../../../../devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:00/LNXVIDEO:00
>     lrwxrwxrwx 1 root root    0 août 18 14:50 LNXVIDEO:01 ->
>     ../../../../devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/LNXVIDEO:01
>     lrwxrwxrwx 1 root root    0 août 18 14:43 module ->
>     ../../../../module/video
>     --w------- 1 root root 4096 août 18 14:50 uevent
>     --w------- 1 root root 4096 août 18 14:50 unbind
>
>   *
>
>     The ACPI video driver attaches normally, and backlight control works
>     as expected.
>
>   *
>
>     Kernel 7.0.0‑29 (backlight stuck at maximum)
>
>   *
>
>     $ ls -l /sys/bus/auxiliary/devices/*/
>
>     /sys/bus/auxiliary/devices/acpi.video_bus.0/:
>     driver -> ../../../../bus/auxiliary/drivers/video
>     firmware_node ->
>     ../../../LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:00/LNXVIDEO:00
>     input/
>     power/
>     subsystem -> ../../../../bus/auxiliary
>     uevent
>
>     /sys/bus/auxiliary/devices/acpi.video_bus.1/:
>     driver -> ../../../bus/auxiliary/drivers/video
>     firmware_node -> ../../LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/LNXVIDEO:01
>     input/
>     power/
>     subsystem -> ../../../bus/auxiliary
>     uevent
>
>   *
>
>     On kernel 7.0.x, the ACPI video devices are no longer bound under
>     |/sys/bus/acpi/drivers/video/|. Instead, they appear under the
>     *auxiliary bus* (|acpi.video_bus.*|). As a result:
>
>   *
>
>     |acpi_video0| disappears

Well, this is not supposed to happen regardless.

The (auxiliary) video driver binds to both devices and it uses the
same platform firmware interfaces as before.

It should register the backlight interface for one of them, but that
doesn't happen for some reason, probably related to the ACPI error
messages you see when running 7.0.x.

>
>   *
>
>     only |intel_backlight| remains
>
>   *
>
>     brightness keys move the slider, but the actual backlight does not
>     change
>
>   *
>
>     ACPI errors appear in dmesg (CreateField length zero,
>     AE_AML_BUFFER_LIMIT, WMID failures)
>
> This matches the regression I initially reported.
>
> If you need additional logs (ACPI, i915, auxiliary bus traces), I can
> provide them.

Please boot the working 6.17.0‑42 kernel again, do

$ ls -l /sys/class/backlight

while running it and send the output of that command.

Also please send boot logs (the output of dmesg after a fresh boot)
from both the working (6.17.0‑42) and failing (7.0.0‑29) kernels.

Thanks!