I have a Thinkpad Edge E130, and the LCD screen's backlight has 15 hardware steps.
$ cat /sys/class/backlight/acpi_video0/max_brightness $ 15
I'm currently running Linux with LXDE as desktop environment, and this is the problem:
- Before login to LXDE, the backlight works fine. With Fn+F6/Fn+F7 I can set all the hardware steps
- After login, I can set only 8 steps. I think that both LXDE and ACPI increase one step for every Fn+F7 pressure (8*2 "=" 15).
I've tried to add the following kernel boot parameters:
acpi_backligh=vendor, thinkpad-acpi.brightness_enable=1(according to this wiki)
In all the case the backlight completely stops to work, so I think that
acpi_backligh=vendor is not helpful in my case.
I have also tried with
video.use_bios_initial_backlight=0 kernel parameter, but nothing seems to happen (always 8 steps).