[ltp] Brightness control on X60

Henrique de Moraes Holschuh linux-thinkpad@linux-thinkpad.org
Wed, 23 May 2007 23:40:08 -0300

On Wed, 23 May 2007, Nathaniel Smith wrote:
> On Wed, May 23, 2007 at 03:54:47PM -0300, Henrique de Moraes Holschuh wrote:
> > On Wed, 23 May 2007, Nathaniel Smith wrote:
> > > In fact, if I use /proc/acpi/ibm/brightness or
> > > /sys/panel/backlight/*/brightness to adjust the backlight, it works
> > > perfectly -- doesn't affect X at all.  So a workaround would be to
> > 
> > Well, if ibm-acpi seems to be working, check if the ACPI video module is
> > loaded, and if it is, try removing it *before* starting X for the first
> > time.
> > 
> > Does that fix the issue?
> Ah-hah, removing the ACPI video driver does indeed seem to fix the
> problem.

File a bug against the distro's kernel.  They need to backport the ACPI
video driver fixes from 2.6.20.

> Now when I press the "up brightness" key the brightness goes all the
> way to maximum (smoothly passing through intermediate stages for a
> nice fading effect), and if I press the "down brightness" key it does
> similarly to the minimum.  If I hit the key quickly twice in
> succession, it will stop at an intermediate level.  ...Is this how
> it's supposed to work?

Well, AFAIK no, it is not.  But I have no idea why it is doing that.

Might be the way the firmware behaves (what happens under Windows?), or
you have two things trying to control the brigness, and interfering with
each other in the most curious way I have ever heard of.

  "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