I have the same problem on a Samsung Q45 notebook.
Without KMS I can set brightness using xbacklight.
With KMS enabled and using xbacklight I get the "No outputs have backlight property" error and I can only set brightness using the setpci method.
/sys/class/backlight is completely empty on this machine.
I'll attach the acpidump and the contents of the sys and proc files mentioned earlier.
I have the same problem on a Samsung Q45 notebook.
Without KMS I can set brightness using xbacklight.
With KMS enabled and using xbacklight I get the "No outputs have backlight property" error and I can only set brightness using the setpci method.
/sys/class/ backlight is completely empty on this machine.
I'll attach the acpidump and the contents of the sys and proc files mentioned earlier.