Backlight regression on Clevo P751DM2-G


the backlight control is still broken on my Clevo P751DM2-G machine, even with 515.76. It does feature an nVidia 1070 Mobile directly attached to an AU Optronics display (i.e., no hybrid mode).

Backlight control is working fine on Windows and even on Linux before the nVidia module loads. Once the nVidia module has been initialized (by starting X), it’s stuck on full brightness.

acpidump and nvidia-bug-report output attached.

acpidump (726.8 KB)
nvidia-bug-report.log.gz (379.0 KB)

Please post the output of
ls -l /sys/class/backlight

lrwxrwxrwx 1 root root 0 Sep 27 18:43 nvidia_0 -> ../../devices/pci0000:00/0000:00:01.0/0000:01:00.0/backlight/nvidia_0

Merely the nvidia_0 node, as you would expect for such a setup.

Still an issue with 525.60.13. Getting pretty old.

This said, there now is a new node in sysfs, even though I haven’t used any different kernel parameters (although I did upgrade to Linux 6.1.1). Both nodes are symlinks to the same directory, though, so technically one of those is redundant. But that’s probably a bugfix for desktops that prefer acpi_video0 and have no notion of the proprietary nvidia_0 node.

ls -l /sys/class/backlight
total 0
lrwxrwxrwx 1 root root 0 Dec 26 06:39 acpi_video0 -> ../../devices/pci0000:00/0000:00:01.0/0000:01:00.0/backlight/acpi_video0
lrwxrwxrwx 1 root root 0 Dec 26 06:39 nvidia_0 -> ../../devices/pci0000:00/0000:00:01.0/0000:01:00.0/backlight/nvidia_0

Kernel parameters, not anything very unusual:

BOOT_IMAGE=/vmlinuz-6.1.1 root=UUID=6e77d2d7-fd5b-4017-8735-1342b0d695e3 ro resume=UUID=f9d8be29-deb8-4040-a506-015669411051 ro verbose nosplash test_suspend=ram memtest=5 rootwait zswap.enabled=1

Neither acpi_video0/brightness nor nvidia_0/brightness change anything still, though.