https://bugzilla.kernel.org/show_bug.cgi?id=55071
Summary: Backlight brightness switching doesn't work on Dell
Inspiron 15R SE (7520)
Product: ACPI
Version: 2.5
Kernel Version: 3.9-rc2
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: Power-Video
AssignedTo: acpi_power-vi...@kernel-bugs.osdl.org
ReportedBy: dannybaum...@web.de
Regression: Yes
Created an attachment (id=95161)
--> (https://bugzilla.kernel.org/attachment.cgi?id=95161)
acpidump output
Since kernel 3.7 I'm unable to control the brightness of the display backlight
on my Dell Inspiron 15R SE (model number 7520) via ACPI methods. Neither using
the hotkeys, nor manually writing values into
/sys/class/backlight/acpi_video[0,1]/brightness changes the brightness. It
works when either writing to intel_backlight/brightness or using kernel 3.6 or
(the preinstalled) Windows 8.
The actual commit that broke it was a57f7f9175b8ccbc9df83ac13860488913115de4 (
ACPICA: Add Windows8/Server2012 string for _OSI method). With that commit,
_BCL exposes a 102 item list instead of an 18 item one, and _BQC always seems
to return the value 100 (which is what breaks the brightness control via
hotkey).
I've attached the output of acpidump, which shows the differentiation in
behaviour between Windows 8 and !Windows 8 done by the AML code; I don't speak
AML fluently enough to interpret what exactly it's doing, though :(
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