https://bugzilla.kernel.org/show_bug.cgi?id=16379
Summary: Display backlight controls not working
Product: ACPI
Version: 2.5
Kernel Version: 2.6.34.1
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: ACPICA-Core
AssignedTo: acpi_acpica-c...@kernel-bugs.osdl.org
ReportedBy: m...@andreas-demmer.de
Regression: No
With kernel 2.6.34, I am unable to change the display brightness: The display
backlight always stays 100% bright even when on battery or using a
energy-saving power plan, sucking my battery dry in no time.
I had a look at /proc/acpi/video to check the brightness information,
but the only folders there are GFX0 and PEGP, none of them contains an LCD
subfolder. :-(
This is what acpi_listen tells me when using the brightness control FN keys:
http://pastebin.com/bTewPC87
It seems that brightness information is stored in:
* GFX0/DD02/brightness
* PEGP/DD02/brightness
Writing "50" into this files (for 50% brightness) does not change the
brightness. Interesting detail: xbacklight now sais the brightness was 50% but
its not. Setting the brightness directly with xbacklight also does not work.
Xorg detects backlight controls: "(II) intel(0): found backlight control
interface /sys/class/backlight/acpi_video1", but there is also a acpi_video0. I
have written different values in the "brightness" file of both entries but
nothing happened.
I suspect this to be an issue of the switchable graphics or the BIOS: My
notebook (HP Envy 14) comes with switchable graphics: A discrete ATI Mobility
Radeon HD 5650 and a integrated Intel Arrandale adapter.
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