Bug 65351

Summary: Can't control laptop screen's brightness when switched to discrete card (Radeon HD 5650) on muxed laptop
Product: Drivers Reporter: bigshot (thequack12)
Component: Video(DRI - Intel)Assignee: Daniel Vetter (daniel)
Status: RESOLVED INSUFFICIENT_DATA    
Severity: high CC: chris, intel-gfx-bugs
Priority: P3    
Hardware: x86-64   
OS: Linux   
Kernel Version: 3.12.0-1-ARCH #1 x86_64 Subsystem:
Regression: No Bisected commit-id:

Description bigshot 2013-11-21 17:50:33 UTC 
When I switch to integrated intel graphics with:
#echo "DIGD" > /sys/kernel/debug/vgaswitcheroo/switch
logout & logback in with only laptop's screen on (obviously),
I _can_ control the laptop screen's 'brightness'. But,
when I switch to discrete Radeon HD 5650 graphics with:
#echo "DDIS" > /sys/kernel/debug/vgaswitcheroo/switch
logout & logback in with both laptop's screen and external monitor 'ON' - laptop screen's brightness becomes full, and I can't decrease the brightness!

I tried:
#echo 1000 > /sys/class/backlight/intel_backlight/brightness
but it doesn't show any effect on brightness of laptop's screen.

Also, the value in /sys/class/backlight/intel_backlight/brightness "jumps" to arbitrary number when I "echo" number into it to "lower" the brightness.

e.g. when I do:
#cd /sys/class/backlight/intel_backlight
#echo 4882 > brightness
the value in 'brightness' file jumps to 13000 and even 64332 or something on second try to lower the brightness.

Finally, let me know if any sort of logs or information is required...
Comment 1 Chris Wilson 2014-03-31 08:27:05 UTC 
If the intel_backlight interface doesn't work when using the discrete GPU (which is not too surprising) have you tried the other backlight interfaces?
Comment 2 Jani Nikula 2014-08-14 11:39:02 UTC 
Timeout. Please reopen if the problem persists with recent kernels.