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

[Henrique de Moraes Holschuh]

On Sun, 23 Dec 2007, Jesse Barnes wrote:
> The Intel X driver now tries to talk to the kernel drivers directly (via 
> the /sys/class/backlight interface) starting with the thinkpad_screen 
> driver, followed by acpi_video1 and acpi_video0.  Depending on how your 
> kernel is configured, this may work perfectly or result in the drivers 
> fighting one another for backlight adjustments.

You are *required* to use the latest devel version 0.18 of thinkpad-acpi
(available in kernel 2.6.24, OR through patches from ibm-acpi.sf.net for
kernels 2.6.20 and above) if you want to use thinkpad_screen in a Lenovo
Thinkpad *61 laptop.

Also, by default, a new enough thinkpad-acpi (0.17? I forget) will refrain
from registering the backlight subdriver if it detects ACPI support is
available (*60 models with very new BIOS, and all *61 models).

> Since on Thinkpads, the kernel method is available (either via the 
> kernel thinkpad driver or ACPI) you should try to use that, but it may 
> be that the acpi_video1 method is your best choice.  You can try that 
> interface by changing the order of the string array in i830_lvds.c 
> around line 67.

Patches to fix the kernel to not export a backlight entry for inactive ACPI
nodes are queued, but really, it is *an extremely bad idea* to hardcode
*anything* of the sort inside X.org.  It needs to be made a configurable
*list* of backlight devices, please.

> If you want to use one of the other methods (which may provide you with 
> more possible backlight levels) you should unload all kernel backlight 
> drivers prior to loading X (or disabling their backlight interfaces as 
> in the case of the thinkpad driver); that may give you a good user 
> experience too...

Agreed.

-- 
  "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