[kde] [Bug 315506] New: PowerDevil backlight control picks wrong /sys/class/backlight control

[Tilman Vogel]

https://bugs.kde.org/show_bug.cgi?id=315506

            Bug ID: 315506
           Summary: PowerDevil backlight control picks wrong
                    /sys/class/backlight control
    Classification: Unclassified
           Product: kde
           Version: 4.8
          Platform: openSUSE RPMs
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: unassigned-bugs at kde.org
          Reporter: tilman.vogel at web.de

Looking at 
https://projects.kde.org/projects/kde/kde-workspace/repository/revisions/master/entry/powerdevil/daemon/backends/upower/backlighthelper.cpp#L46
shows that for Linux 3.x, the whitelist approach is never used and instead the
available kernel backlight controls are ranked purely by their type and
"firmware > platform > raw".

In my configuration, however, the binary nvidia driver registers
/sys/class/backlight/acpi_video0 which is "firmware" but unfortunately is
non-functional and I don't know a way to unregister that sys-control.
Nevertheless, I also have /sys/class/backlight/nvidia_backlight which is
provided by 
https://github.com/guillaumezin/nvidiabl
which works and is a "raw" control.
So, powerdevil does not pick it in favor of the non-functional device.
Also, in a scenario where there are actually multiple "equivalent" (type-wise)
sys-controls, it would just pick the alphabetically highest which is a
non-robust guess.
I think, there should be a way to override this or even better offer all
available controls (with an option to hide some).


Reproducible: Always

Steps to Reproduce:
1. Install KDE 4.8.5 on an ASUS G55VW (Nvidia GTX 660M with binary drivers)
2. Install nvidiabl (see above)

Actual Results:  
KDE brightness controls don't have any effect.

Expected Results:  
KDE brightness controls do take effect.

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