Comment 49 for bug 872652

Dear All,

I just tested this last patch, and it works for me on my ASUS UL20A. (intel GMA 4500HD)

below some detailed infos:

$ uname -a
Linux rgw2 3.0.0-13-generic #22+kamal~fix~stuck~backlight3-Ubuntu SMP Fri Nov 18 01:04:58 UT i686 i686 i386 GNU/Linux
$ cat /proc/cmd*
BOOT_IMAGE=/boot/vmlinuz-3.0.0-13-generic root=UUID=212683b0-1b69-4969-a259-665b422074e3 ro quiet splash acpi_backlight=vendor vt.handoff=7
~$ ls -l /sys/class/backlight
total 0
lrwxrwxrwx 1 root root 0 2011-11-23 13:41 asus_laptop -> ../../devices/platform/asus_laptop/backlight/asus_laptop
lrwxrwxrwx 1 root root 0 2011-11-23 13:41 intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight

My Hardware: ASUS UL20A
$ lspci -nn
00:02.0 VGA compatible controller [0300]: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller [8086:2a42] (rev 07)
00:02.1 Display controller [0380]: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller [8086:2a43] (rev 07)

I use acpi_backlight=vendor, to have backlight control button work.
Without this option, the buttons are recognized, but have no dimming effect and cause somewhere a waiting loop between 2 actions. Also, sometime the screen switch off without any reason.
Manual dimming can be done using command
sudo setpci -s 00:02.0 F4.B=xx
where xx is dimming percentage.

**** before the patch
$ xset s activate => switch off the screen
lock screen, and wait for screen off, then unlock: the screen stay stucked at brightness 0 (off)
**** after the patch
$ xset s activate => swicth off then on the screen
lock screen, and wait for screen off, then unlock: the screen switch back on at previous dim level.

without acpi_backlight=vendor and without the patch the behaviour, seems quite normal, except that brightness control is not possible with the keyboard, brightness is off or max.

CONCLUSION:
-Default systems works without dimming control
-Dimming control requires acpi_backlight=vendor which activates the bug, and proposed patch is ok.