On 2011-11-10 at 19:36 -0500, Taylor Hedberg wrote:
Sebastian Schwarz, Thu 2011-11-10 @ 16:36:54+0100:
The bug can easily triggered in X by running:
xset dpms force off
Yes, this is the same behavior that I'm seeing. Writing the max_brightness value into the sysfs brightness file restores normal backlight brightness. I can also restore it with `xbacklight -set 100`.
After running `xbacklight -set 100` my backlight is at the previous brightness level, which is 57% and not at the 100% xbacklight should set it to.
I found this I my dmesg output:
[Firmware Bug]: Duplicate ACPI video bus devices for the same VGA controller, please try module parameter "video.allow_duplicates=1"if the current driver doesn't work.
But I also haven't tried this, as the incorrect brightness has not annoyed me enough, yet.
I have this message in my dmesg output as well, but unfortunately, setting the mentioned module parameter doesn't have any effect on the problems I'm seeing.
It doesn't do anything over here, too. However downgrading the kernel to 3.0.7-1 helps. There are a few interesting things: % pacman -Q linux xorg-xbacklight linux 3.0.7-1 xorg-xbacklight 1.1.2-2 % xbacklight -get No outputs have backlight property % cat /sys/class/backlight/intel_backlight/{,max_}brightness cat: /sys/class/backlight/intel_backlight/brightness: No such file or directory cat: /sys/class/backlight/intel_backlight/max_brightness: No such file or directory So 3.1 has probably some new backlight code, which does not work as it should. And indeed there are two threads on the linux.kernel newsgroup[1, 2] and one on the LKML[3] with an explanation, a patch[4] and a couple of bug reports[5, 6, 7]. I have not tested the patch yet, but is seems to deal with the issue at hand. [1]: https://groups.google.com/group/linux.kernel/browse_thread/thread/28296924e8... [2]: https://groups.google.com/group/linux.kernel/browse_thread/thread/fde3079d9f... [3]: https://lkml.org/lkml/2011/9/19/381 [4]: https://lkml.org/lkml/diff/2011/10/25/473/1 [5]: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/872652 [6]: https://launchpad.net/~kamalmostafa/+archive/stuck-backlight [7]: https://bugs.freedesktop.org/show_bug.cgi?id=41926