[kde] [Bug 348882] New: KDE cannot set backlight anymore, kernel can

[azrdev at googlemail.com]

https://bugs.kde.org/show_bug.cgi?id=348882

            Bug ID: 348882
           Summary: KDE cannot set backlight anymore, kernel can
           Product: kde
           Version: 4.11.5
          Platform: Archlinux Packages
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: unassigned-bugs at kde.org
          Reporter: azrdev at googlemail.com

Since the last KDE update[1] on my archlinux, KDE cannot set the screen
backlight anymore. When `echo`ing to /sys/class/backlight/radeon_bl0/brightness
it works fine (as before), but if I press the XF86MonBrightness{Down,Up}
buttons, or use the battery plasma widget to adjust the brightness, nothing
happens except some log messages [2] about backlighthelper being started. Those
had been there identically when it still worked.
The brightness control of the battery widget initially shows 0%, previously it
showed the actual current level.

uname: Linux host 4.0.4-2-ARCH #1 SMP PREEMPT Fri May 22 03:05:23 UTC 2015
x86_64 GNU/Linux
As in the current archlinux repos, my system has mixed KDE4 and KF5 components
running: I can tell the versions if there's anything specific of interest.
My graphics card is the embedded Radeon HD 7340 in my E2-1800 Zacate CPU, see
[3]

[1] excerpt from /var/log/pacman.log :
[2015-05-13 09:46] [ALPM] upgraded kdebase-workspace (4.11.18-1 -> 4.11.19-1)
[2015-05-13 09:46] [ALPM] upgraded kdebase-plasma (15.04.0-3 -> 15.04.1-1)

[2] from journal:
Jun 08 15:39:50 host dbus[236]: [system] Activating service
name='org.kde.powerdevil.backlighthelper' (using servicehelper)
Jun 08 15:39:50 host org.kde.powerdevil.backlighthelper[16793]:
QDBusConnection: system D-Bus connection created before QCoreApplication.
Application may misbehave.
Jun 08 15:39:50 host dbus[236]: [system] Successfully activated service
'org.kde.powerdevil.backlighthelper'

[3] sudo lspci -nnk -v -s 00:01.0  # my graphics card
00:01.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc.
[AMD/ATI] Wrestler [Radeon HD 7340] [1002:9808] (prog-if 00 [VGA controller])
        Subsystem: Lenovo Device [17aa:5105]
        Flags: bus master, fast devsel, latency 0, IRQ 32
        Memory at e0000000 (32-bit, prefetchable) [size=256M]
        I/O ports at 3000 [size=256]
        Memory at f0b00000 (32-bit, non-prefetchable) [size=256K]
        Expansion ROM at <unassigned> [disabled]
        Capabilities: [50] Power Management version 3
        Capabilities: [58] Express Root Complex Integrated Endpoint, MSI 00
        Capabilities: [a0] MSI: Enable+ Count=1/1 Maskable- 64bit+
        Capabilities: [100] Vendor Specific Information: ID=0001 Rev=1 Len=010
<?>
        Kernel driver in use: radeon
        Kernel modules: radeon


Reproducible: Always

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