LCD backlight brightness control only works until boot starts

[rekado]

Binary package hint: acpi-support

I'm running Intrepid Ibex Beta from a fresh install on a Haier A61 laptop (probably a rebranded Clevo type). The LCD's brightness can be lowered by pressing Fn+F8 and increased by pressing Fn+F7. This works right until Ubuntu boots from GRUB. While in GRUB the brightness control works.

When booting with acpi=off the backlight control works, however I lose all ACPI advantages, so this is no fix.
Booting with acpi=ht also leaves the brightness control intact but the system won't finish booting. Instead it stops with the light brown pre-desktop; the mouse can still be moved but I cannot even switch to another tty anymore.

All the other boot-options like pci=noacpi, acpi=noirq, pnpacpi=off, noapic or nolapic have no effect.

None of the workarounds mentioned in the forums or on similar bug reports worked. I've been trying for almost a year and collected all kinds of information but no proposed workaround fixed the issue.

---
Output of lsb_release -rd:

Description: Ubuntu intrepid (development branch)
Release: 8.10

---
Output of apt-cache policy acpi-support

acpi-support:
  Installed: 0.112
  Candidate: 0.112
  Version table:
 *** 0.112 0
        500 http://de.archive.ubuntu.com intrepid/main Packages
        100 /var/lib/dpkg/status

[rekado (rekado)]

This happened when trying to copy the acpi directory to tmp:

cp: cannot open `/proc/acpi/event' for reading: Device or resource busy

Hope it doesn't make a difference.

[rekado (rekado)]

This is the related thread with information what fixes I tried:

http://ubuntuforums.org/showthread.php?p=5915703

[rekado (rekado)]

Is there any more information I shall provide? How can I try debugging it on my own?

[rekado (rekado)]

I'm now on Arch and with a very simple installation the error is the same. As soon as acpid is loaded the brightness cannot be changed anymore.

cat /proc/acpi/video/IGD/LCD/info

yields following output

device_id: 0x0110
type: UNKNOWN
known by bios: no

[rekado (rekado)]

"Good news, everyone..."

Playing with the options explained here http://www.columbia.edu/~ariel/acpi/acpi_howto.txt I finally managed to get it done.

I added the boot option acpi_osi= to my kernel line in /boot/grub/menu.lst and now it works. By default acpi_osi is used to hand over a string to the BIOS to pretend we are running Windows NT. Providing an empty string apparently leaves it as it is.

[rekado (rekado)]

Fixed with kernel boot option "acpi_osi=" (without quotation marks).