the backlighthelper process is not getting started.


nerdy_kid@jesse-laptop:~$ /usr/lib/kde4/libexec/backlighthelper 
kernel backlight support found in "/sys/class/backlight/acpi_video0"
nerdy_kid@laptop:~$ cd /sys/class/backlight/acpi_video0
nerdy_kid@laptop:/sys/class/backlight/acpi_video0$ ls
total 0
-r--r--r-- 1 root root 4096 2010-12-27 11:02 actual_brightness
-rw-r--r-- 1 root root 4096 2010-12-27 11:02 bl_power
-rw-r--r-- 1 root root 4096 2010-12-27 10:25 brightness
lrwxrwxrwx 1 root root    0 2010-12-27 11:02 device -> ../../../LNXSYSTM:00/LNXSYBUS:00/PNP0A03:00/device:2d/LNXVIDEO:00/device:30
-r--r--r-- 1 root root 4096 2010-12-27 11:02 max_brightness
drwxr-xr-x 2 root root    0 2010-12-27 11:02 power
lrwxrwxrwx 1 root root    0 2010-12-27 11:02 subsystem -> ../../../../class/backlight
-rw-r--r-- 1 root root 4096 2010-12-27 11:02 uevent
nerdy_kid@laptop:/sys/class/backlight/acpi_video0$ cat brightness 
7
nerdy_kid@laptop:/sys/class/backlight/acpi_video0$ cat max_brightness 
7
nerdy_kid@laptop:/sys/class/backlight/acpi_video0$ sudo -i
[sudo] password for nerdy_kid: 
root@laptop:~# echo 5 > /sys/class/backlight/acpi_video0/brightness 
root@laptop:~# cat brightness 
5
root@laptop:~#


doing the above correctly sets and queries the lcd brightness, so it is a KDE issue.

Reassigning to Lukas

Any conditions under which to reproduce this? "powerdevil will randomly loose control" doesn't help much :)

Created attachment 55364 [details]
xsession error file.

Created attachment 55365 [details]
syslog resume from standby

I can't reproduce it reliably yet, but it does seem to have something to do with the suspend/resume cycle.  Lines 301 and 203 are of interest in the syslog.

I tried manually starting the backlight helper as root, but it still did not fix it.

I apologize for my string of comments, but I just tried manually setting the brightness via dbus (qdbusviewer) and it failed with the same "kded(10126) PowerDevilUPowerBackend::setBrightness: org.kde.powerdevil.backlighthelper.setbrightness failed" in .xsession-errors.

Also, I notice when it does work the backlighthelper process is not always running, it will normally start as soon as I adjust the brightness, and then exit about 5 seconds after I have ceased adjusting the brightness.  Is it supposed to do that?

added info.

For me plasma widget is utterly broken - the brightness slider doesnt work. When I try to adjust the brightness slider PolicyKit eats 100% cpu for a few seconds then the slider is back at maximum.

In xsession-errors I have the same "kded(3595) PowerDevilUPowerBackend::setBrightness: org.kde.powerdevil.backlighthelper.setbrightness failed" lines.

But changing brightness on profile change works perfectly a in xssesion-errors I got
"Debug message from helper: brightness: 4 
Debug message from helper: max brightness: 7 
Debug message from helper: data contains: QVariant(int, 57) "

I am using KDE 4.6 RC2 and I have nVidia Corporation GT216 [GeForce GT 330M]

polkitd cpu spikes up to about 7% for me.  I think it is authentication bug with Kauth actually, but I'm not a programmer.  My brightness does not change at all once this bug happens, not even with power profile changes.

It seems to have something to do with suspend/resume.  Like today, everything was working fine, I suspended the laptop (taking note of the state of the brightness slider) and when I resumed it, the brightness control was broken.

killing and restarting kded4 fixes the issue temporarily.

still effects 4.6 final

ok, can reproduce it!  With everything working, suspend the laptop -- it has to be a laptop I am pretty sure.  Now, turn it back on and immediately begin hitting the key combo to raise/lower brightness.  When KDE comes back up, the brightness control no longer works and "kded(17585) PowerDevilUPowerBackend::brightness: org.kde.powerdevil.backlighthelper.brightness failed " is littered all through the terminal output from kded4.  Killing kded4 and restarting it fixes it until the above is done again, but it also produces this line: 

 "QDBusConnection: name 'org.kde.powerdevil.backlighthelper' had owner '' but we thought it was ':x.xxxx'" 

which I thought was interesting.  

Suspending the laptop while it is plugged in, unplugging it and resuming or vice versa also triggers the bug, as power devil tries changing the brightness too soon I guess.

This should be fixed using latest NVIDIA beta driver, can you test please?

I have an NVIDIA Quadro K1000M and with the latest stable driver (310.40, which used to be the "beta" referred to above) can confirm that issue is fixed for me. I used Fedora 18, and be aware the latest driver in YUM is still only 304.something and is too old to support changing brightness.