Comment 5 for bug 954661

Mario Limonciello (superm1) wrote :

At least to me this doesn't look like it's at all caused by a userspace interpretation problem, it's caused only by this intel_backlight interface. It's defaulting to the maximum value it can be set to (4882).

* The button presses do actually translate into the values of /sys/class/backlight/acpi_video0/brightness changing between 0 and 15 as they should.

Manually putting any numbers into /sys/class/backlight/intel_backlight/brightness smaller than max_brightness allows the ACPI video control to work*.

Now most values above 0 set for intel_backlight seem to cause a horrible flicker on the screen as the ACPI values are changed.

I compared to another machine with a properly functioning backlight control, and it's defaulting to a more sane 118 (out of max 976) on it's intel_backlight/brightness value. So for whatever reason, the intel_backlight value that is defaulted on this laptop is 4882.