In the output of `xrandr --verbose` there should be a few lines looking something like this:
BACKLIGHT_CONTROL: kernel
supported: native legacy combination kernel
BACKLIGHT: 15 (0x0000000f) range: (0,15)
What are your corresponding lines?
Does the number on the BACKLIGHT line change?
Do you have one or more files called "brightness" in some subdirectory under /proc/acpi/video/ (the exact location below that varies)? Where are they? What do they say? Does it change?
In the output of `xrandr --verbose` there should be a few lines looking something like this:
BACKLIGHT_CONTROL: kernel
supported: native legacy combination kernel
BACKLIGHT: 15 (0x0000000f) range: (0,15)
What are your corresponding lines?
Does the number on the BACKLIGHT line change?
Do you have one or more files called "brightness" in some subdirectory under /proc/acpi/video/ (the exact location below that varies)? Where are they? What do they say? Does it change?