ACPI and backlight

Marius Gedminas marius at pov.lt
Sun Jan 9 22:05:44 UTC 2005


I am looking for ACPI gurus.

I run hoary, kernel 2.6.10 with acpi on a Thinkpad T23.  ACPI sleep
works (only it makes the system clock go twice as fast for some reason,
so I added hwclock --hctosys into sleep.sh to restore it after resuming).

I do no want my laptop to go to sleep when I close the lid, so I made my
lid.sh do only 'xset dpms force off'.  It works when I push the lid
button manually (without that 'xset dpms force off' in lid.sh, only the
backlight goes off but I can still see windows etc. if I look closely).

A minor annoyance is that 'xset dpms force on' does not do anything, so
I have to hit a key or move the mouse the get the screen back when I
release the lid button.

Now the mystery: the backlight does not go off if I actually close the
lid.  I can see that lid.sh is run -- xset dpms force off works so I get
a black shining screen.

I do not understand how closing the lid is different from just pushing
the little "lid is closed" button, and what exactly controls the
backlight (acpi? bios? hardware?).  I can, however, reliably reproduce
this:

  * pushing the lid button by hand always turns off the backlight
  * closing the lid while in BIOS or in GRUB menu always turns off the
    backlight
  * closing the lid once the ACPI module is loaded does not turn off the
    backlight (this also happens with Warty Live CD that uses 2.6.7),
    even though it blanks the screen.

Any ideas?

I will try booting with APM (acpi=off on the command line), and I will
try booting my old Debian unstable system that used 2.4.x and apm.

Marius Gedminas
-- 
EMACS is a good OS.  The only thing it lacks is a decent text-editor.
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