https://bugs.kde.org/show_bug.cgi?id=399646
Bug ID: 399646
Summary: Brightness control adjusts the wrong backlight control
(multiple GPUs)
Product: Powerdevil
Version: 5.14.0
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: plasma-b...@kde.org
Reporter: bastian.beisc...@rwth-aachen.de
Target Milestone: ---
When using my laptops (Lenovo W520) FN-keys to adjust the display brightness
the OSD shows up and the sliders change, but the display brightness does not.
This laptop has two physical GPUs (Intel + NVIDIA), depending on the BIOS
settings you can use either Intel, NVIDIA by themselves or both. I have a PRIME
setup where I'm using both GPUs, the Intel GPU is the main one and the other
one is normally asleep, unless I plug in an external monitor.
I have to providers for backlight in /sys/class:
/sys/class/backlight/intel_backlight
/sys/class/backlight/nv_backlight
Both have "type" = "raw".
Even when I don't have a secondary monitor connected (and the NVIDIA GPU isn't
used at all) I can see that the nv_backlight/brightness value changes when
using the brightness control, but that's the wrong one!
Now I have had a quick glance at the code of the brightness controls, which
appears to either use a whitelist of backlight providers, or goes through all
the providers and picks the first one (since they both have type raw).
Because there surely are users who have NVIDIA as a primary GPU and Intel as a
secondary one, it is possible that a hardcoded list of preferences will never
satisfy all parties. Maybe a setting in ~/.config could be used to specify the
correct device?
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