Backlight Brightness on Asus X55u notebook cannot be adjusted

I installed LEAP 15.1 on a ASUS X55u notebook. Adjusting the brightness via power management has no effect. Also there is a failure during boot:


 systemctl status systemd-backlight@backlight:acpi_video0.service
● systemd-backlight@backlight:acpi_video0.service - Load/Save Screen Backlight Brightness of backlight:acpi_video0
   Loaded: loaded (/usr/lib/systemd/system/systemd-backlight@.service; static; vendor preset: disabled)
   Active: failed (Result: exit-code) since Thu 2019-10-03 21:13:55 CEST; 3h 34min ago
     Docs: man:systemd-backlight@.service(8)
 Main PID: 688 (code=exited, status=1/FAILURE)

Okt 03 21:13:54 linux-nudl systemd[1]: Starting Load/Save Screen Backlight Brightness of backlight:acpi_video0...
Okt 03 21:13:55 linux-nudl systemd[1]: systemd-backlight@backlight:acpi_video0.service: Main process exited, code=exited, sta>
Okt 03 21:13:55 linux-nudl systemd[1]: Failed to start Load/Save Screen Backlight Brightness of backlight:acpi_video0.
Okt 03 21:13:55 linux-nudl systemd[1]: systemd-backlight@backlight:acpi_video0.service: Unit entered failed state.
Okt 03 21:13:55 linux-nudl systemd[1]: systemd-backlight@backlight:acpi_video0.service: Failed with result 'exit-code'.

Here infos about the graphics
/usr/sbin/hwinfo --gfxcard

26: PCI 01.0: 0300 VGA compatible controller (VGA)              
  [Created at pci.386]
  Unique ID: vSkL.7h3hPhINcV6
  SysFS ID: /devices/pci0000:00/0000:00:01.0
  SysFS BusID: 0000:00:01.0
  Hardware Class: graphics card
  Model: "ATI Wrestler [Radeon HD 7340]"
  Vendor: pci 0x1002 "ATI Technologies Inc"
  Device: pci 0x9808 "Wrestler [Radeon HD 7340]"
  SubVendor: pci 0x1043 "ASUSTeK Computer Inc."
  SubDevice: pci 0x14e7 
  Driver: "radeon"
  Driver Modules: "radeon"
  Memory Range: 0xd0000000-0xdfffffff (ro,non-prefetchable)
  I/O Ports: 0xf000-0xf0ff (rw)
  Memory Range: 0xfeb00000-0xfeb3ffff (rw,non-prefetchable)
  Memory Range: 0x000c0000-0x000dffff (rw,non-prefetchable,disabled)
  IRQ: 30 (627591 events)
  I/O Ports: 0x3c0-0x3df (rw)
  Module Alias: "pci:v00001002d00009808sv00001043sd000014E7bc03sc00i00"
  Driver Info #0:
    Driver Status: radeon is active
    Driver Activation Cmd: "modprobe radeon"
  Config Status: cfg=new, avail=yes, need=no, active=unknown

Any advice apreciated

Hi
Just check if there is another backlight service running (there should be an asus one), else try adding the following kernel boot option (via YaST -> Bootloader);


acpi_osi=\"!Windows 2012\"

Indeed there are four services
systemctl list-units --type service | grep backlight


● systemd-backlight@backlight:acpi_video0.service loaded failed failed  Load/Save Screen Backlight Brightness of backlight:acpi_video0               
● systemd-backlight@backlight:acpi_video1.service loaded failed failed  Load/Save Screen Backlight Brightness of backlight:acpi_video1               
  systemd-backlight@backlight:asus-nb-wmi.service loaded active exited  Load/Save Screen Backlight Brightness of backlight:asus-nb-wmi               
  systemd-backlight@backlight:radeon_bl0.service  loaded active exited  Load/Save Screen Backlight Brightness of backlight:radeon_bl0  

How to proceed from here?

else try adding the following kernel boot option (via YaST -> Bootloader) acpi_osi="!Windows 2012"

I tried but it had no effect.

Hi
I would disable and mask the first two;


systemctl disable acpi_video0.service acpi_video1.service
systemctl mask acpi_video0.service acpi_video1.service

Then disable either of the asus or radeon and reboot and see which one will work. Once you have the right one, disable and mask.

Thanks. This pointed in the right direction. Actually I could solve the backlight issue now with those two grub2 options:

acpi_backlight=video
acpi_osi=