Comment 201 for bug 568611

ASUS UL30A running oneiric with 2.6.38-9-generic amd64 kernel:

[ 0.000000] Linux version 2.6.38-9-generic (buildd@king) (gcc version 4.5.2 (Ubuntu/Linaro 4.5.2-8ubuntu4) ) #43+kamal~mjgbacklight4-Ubuntu SMP Fri Apr 29 04:33:59 UTC 2011 (Ubuntu 2.6.38-9.43+kamal~mjgbacklight4-generic 2.6.38.4)

Pressing Fn+F6 (Brightness Up) is catched by XFCE and notification for brightness up is shown. But brightness does not change and kernel says:

[ 803.043216] ACPI Error: Result stack is empty! State=ffff880134fc4800 (20110112/dswstate-98)
[ 803.043236] ACPI Exception: AE_AML_NO_RETURN_VALUE, Missing or null operand (20110112/dsutils-646)
[ 803.043247] ACPI Exception: AE_AML_NO_RETURN_VALUE, While creating Arg 1 (20110112/dsutils-763)
[ 803.043261] ACPI Error: Method parse/execution failed [\_SB_.PCI0.VGA_.UPBL] (Node ffff880137638550), AE_AML_NO_RETURN_VALUE (20110112/psparse-536)
[ 803.043284] ACPI Error: Method parse/execution failed [\_SB_.PCI0.SBRG.EC0_._Q0F] (Node ffff88013763fcd0), AE_AML_NO_RETURN_VALUE (20110112/psparse-536)

On Fn+F5 (Brightness Down):

[ 833.535486] ACPI Error: Result stack is empty! State=ffff88012f7c7800 (20110112/dswstate-98)
[ 833.535505] ACPI Exception: AE_AML_NO_RETURN_VALUE, Missing or null operand (20110112/dsutils-646)
[ 833.535517] ACPI Exception: AE_AML_NO_RETURN_VALUE, While creating Arg 1 (20110112/dsutils-763)
[ 833.535531] ACPI Error: Method parse/execution failed [\_SB_.PCI0.VGA_.DWBL] (Node ffff880137638578), AE_AML_NO_RETURN_VALUE (20110112/psparse-536)
[ 833.535554] ACPI Error: Method parse/execution failed [\_SB_.PCI0.SBRG.EC0_._Q0E] (Node ffff88013763fca8), AE_AML_NO_RETURN_VALUE (20110112/psparse-536)

Now I have two backlight interfaces:

17:01 root@lucek:backlight# ls -l
razem 0
lrwxrwxrwx 1 root root 0 2011-05-20 16:47 asus_laptop -> ../../devices/platform/asus_laptop/backlight/asus_laptop
lrwxrwxrwx 1 root root 0 2011-05-20 16:47 intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight

Removing of asus-laptop module gave me black screen with no backlight at all. Loading it back does not change situation.

Amount of possible step for intel_backlight scares me:

17:03 root@lucek:intel_backlight# cat max_brightness
1992060