https://bugzilla.kernel.org/show_bug.cgi?id=66501
Bug ID: 66501
Summary: 8086:2a42 [Asus UL80VT] Backlight control does not
work with Intel integrated card, but there are entries
in /sys/class/backlight
Product: ACPI
Version: 2.5
Kernel Version: 3.11.0-14-generic #21-Ubuntu
Hardware: All
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: Power-Video
Assignee: acpi_power-vi...@kernel-bugs.osdl.org
Reporter: gmill...@gmail.com
Regression: No
Created attachment 117421
--> https://bugzilla.kernel.org/attachment.cgi?id=117421&action=edit
dmesg
The screen brightness control has apparently never worked off-the-shelf on this
laptop released in 2009, Asus UL80VT-A1, which is an NVIDIA Optimus laptop (2
graphic cards). The use of the discrete Nvidia card is managed by Bumblebee
(https://wiki.ubuntu.com/Bumblebee). It used to work with the workaround
suggested at
http://wiki.daviddarts.com/Ubuntu_Maverick_on_the_Asus_UL30VT#Screen_Brightness
which modifies asus-brn-down.sh to use the "setpci" method. When the hotkeys
are triggered, there is no brightness change but the KDE popup notification
appears.
$ ls /sys/class/backlight/
acpi_video0 acpi_video1 intel_backlight
$ cat /sys/class/backlight/intel_backlight/max_brightness
2583660
$ cat /sys/class/backlight/intel_backlight/brightness
121584
The intel_backlight interface works, by echoing a value between 0 and 2583660.
$ cat /sys/class/backlight/acpi_video0/brightness
6
$ cat /sys/class/backlight/acpi_video0/max_brightness
15
$ cat /sys/class/backlight/acpi_video0/device/device
0x2a42
$ cat /sys/class/backlight/acpi_video1/brightness
15
$ cat /sys/class/backlight/acpi_video1/max_brightness
15
$ cat /sys/class/backlight/acpi_video1/device/device
0x0a74
By echoing a value between 0 and 15, the two acpi_video interfaces do not
change the screen brightness.
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