[ltp] Bug#448467: xserver-xorg-video-intel: Thinkpad brightness keys don't work

[Henrique de Moraes Holschuh]

On Mon, 29 Oct 2007, Marcus Better wrote:
> The brightness control keys on my Thinkpad R60 stopped working in X
> some time ago. I have probably upgraded both kernel and X.org since
> then, and don't know exactly when it broke.

The *60 and *61 series of ThinkPads require proper brightness support using
the ACPI specification.  Unfortunately, the kernel ACPI video driver is not
quite there yet, and you need at the very least the 2.6.22 version of ACPI
video to have any chance of it working most of the time.

They can also operate using thinkpad-acpi 0.18 (not merged into mainline
yet), although that requires a module parameter, as thinkpad-acpi 0.18
disables its brightness driver by default when it detects there is standard
ACPI brightness control in the BIOS.

thinkpad-acpi patches are at http://ibm-acpi.sf.net.

> Pressing the keys in an X session now only causes a short flicker, but
> does not affect the brightness. However the KDE on-screen display
> seems to think everything is fine since I can control the level it
> reports.

That's because the KDE on-screen displays does something Not Nice and
accesses the thinkpad NVRAM directly.

> I can control the brightness at least reasonably well with
>   echo 50 > /sys/devices/virtual/backlight/acpi_video1/brightness
> except that levels below 30 don't seem to have any effect.

That might be the correct behaviour.  The BIOS has some non-linear mapping
tables to translate from 0-100 to 0-7/0-15 (depending on thinkpad model).
It could be that anything from 0 to 30 maps to the first brightness level in
the hardware.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh