I've met the following problem: normally my T400 (Lenovo Thinkpad) has 16 steps of brightness, and Windows utilizes it correctly.

After a fresh install & minor tweaks Mint 12 (which is based on 11.10 Ubuntu) I only had 6 steps which was way to few.

Listing /sys/class/backlight showed 3 entried. I removed the acpi-tools package, one of the disapperared - and I now have 10 steps!

Therefore I think if I can reduce the entries to 1 I'm going to have 16 steps, since the stepping will be 1 instead of 2 (or 3).

/sys/class/backlight/

intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight
thinkpad_screen -> ../../devices/virtual/backlight/thinkpad_screen

The problem is that I'm unable to trace back what are the configs / daemons / kernel options triggers these two.

More strangely, I discovered a strange behaviour. I monitored

watch -n1 "cat /sys/class/backlight/thinkpad_screen/actual_brightness"

and

watch -n1 "cat /sys/class/backlight/intel_backlight/actual_brightness"

while changing the brightness with FN+home/end combinations from max to min. The outcome is the following:

brighness   intel       thinkpad
---------   -----       --------
MAX         2408475         7
|           1955115         5
|           1435640         3
|           1246740         1
|           1086175         0
|           1010615         6
|           859495          4
|           689485          2
v           481695          0
MIN         217235          0


brighness   intel       thinkpad
---------   -----       --------
MIN         217235          0
|           481695          2
|           689485          4
|           859495          6
|           1010615         7
|           1086175         1
|           1246740         3
|           1435640         5
v           1955115         7
MAX         2408475         0

When stepping from MIN to MAX, there's no difference between the last 2 steps.

Also, the OSD icon (Cinnamon desktop, default theme) goes from full to min in 4 steps and from full to min once again in 4 steps.

So... it seems that the intel entry is working correctly, showing correct values. The thinkpad entry however twists the things and even showing incorrect values.

Does anyone have any idea how to get rid of the thinkpad entry?

System data: Linux Mint 12 3.0.0-16 kernel Lenovo ThinkPad T400 Cinnamon 1.4 desktop

For any additional info, please tell me what do you need.

EDIT

I'm sorry, I forgot to mention, I added acpi_backlight=vendor to GRUB cmdline as well, this is the result of the semi-better working than the default.