Brightness Controls Disappeared: PowerDevil not working properly

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1

My brightness controls have disappeared and PowerDevil is logging problems such as:

jun 29 18:18:03 hp-laptop-15da0xxx systemd[1695]: Starting plasma-powerdevil.service - Powerdevil...
jun 29 18:18:03 hp-laptop-15da0xxx dbus-daemon[1011]: [system] Activating service name='org.kde.powerdevil.discretegpuhelper' requested by ':1.214' (uid=1000 pid=12365 comm="/usr/lib/x86_64-linux-gnu/libexec/org_kde_powerdev" label="unconfined") (using servicehelper)
jun 29 18:18:03 hp-laptop-15da0xxx dbus-daemon[1011]: [system] Successfully activated service 'org.kde.powerdevil.discretegpuhelper'
jun 29 18:18:03 hp-laptop-15da0xxx dbus-daemon[1011]: [system] Activating service name='org.kde.powerdevil.chargethresholdhelper' requested by ':1.214' (uid=1000 pid=12365 comm="/usr/lib/x86_64-linux-gnu/libexec/org_kde_powerdev" label="unconfined") (using servicehelper)
jun 29 18:18:03 hp-laptop-15da0xxx dbus-daemon[1011]: [system] Successfully activated service 'org.kde.powerdevil.chargethresholdhelper'
jun 29 18:18:03 hp-laptop-15da0xxx dbus-daemon[1011]: [system] Activating service name='org.kde.powerdevil.backlighthelper' requested by ':1.214' (uid=1000 pid=12365 comm="/usr/lib/x86_64-linux-gnu/libexec/org_kde_powerdev" label="unconfined") (using servicehelper)
jun 29 18:18:03 hp-laptop-15da0xxx org.kde.powerdevil.backlighthelper[12390]: org.kde.powerdevil: no kernel backlight interface found
jun 29 18:18:03 hp-laptop-15da0xxx dbus-daemon[1011]: [system] Successfully activated service 'org.kde.powerdevil.backlighthelper'
jun 29 18:18:03 hp-laptop-15da0xxx org_kde_powerdevil[12365]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
jun 29 18:18:03 hp-laptop-15da0xxx org_kde_powerdevil[12365]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed
jun 29 18:18:03 hp-laptop-15da0xxx systemd[1695]: Started plasma-powerdevil.service - Powerdevil.
jun 29 18:18:03 hp-laptop-15da0xxx org_kde_powerdevil[12365]: org.kde.powerdevil: Handle button events action could not check for screen configuration
jun 29 18:18:03 hp-laptop-15da0xxx org_kde_powerdevil[12365]: org.kde.powerdevil: The profile  "AC" tried to activate "DimDisplay" a non-existent action. This is usually due to an installation problem, a configuration problem, or because the action is not supported
jun 29 18:18:03 hp-laptop-15da0xxx org_kde_powerdevil[12365]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"

I have tried reinstalling PowerDevil to no avail.

Last week I installed a couple of updates which caused my Kubuntu system to fail to adding the kernel directive “nomodeset”. Following advice found online, I then decided to disable Nouveau via a config file in /etc/modprobe.d, and then attempted to change to nvidia proprietary drivers. This last step was a disaster which I managed to resolve by purging nvidia packages from the system using “apt purge nvidia*”. This allowed the system to start again. Finally, I decided to experiment with Nouveau settings again and found that the original settings worked fine. At this point I am not sure what has changed on my system - I’ve undone everything that I did manually. The only candidate is that I have purged some nvidia packages that were there before.

How can I get my brightness controls back?

OS: Ubuntu 24.04.2
KDE Plasma: 5.27.12
KDE Frameworks: 5.115.0
Qt: 5.15.13

00:02.0 VGA compatible controller: Intel Corporation UHD Graphics 620 (rev 07) (prog-if 00 [VGA controller])
Subsystem: Hewlett-Packard Company UHD Graphics 620
Flags: bus master, fast devsel, latency 0, IRQ 255
Memory at a2000000 (64-bit, non-prefetchable) [size=16M]
Memory at b0000000 (64-bit, prefetchable) [size=256M]
I/O ports at 6000 [size=64]
Expansion ROM at 000c0000 [virtual] [disabled] [size=128K]
Capabilities:
Kernel modules: i915

01:00.0 3D controller: NVIDIA Corporation GM108M [GeForce MX110] (rev a2)
Subsystem: Hewlett-Packard Company GM108M [GeForce MX110]
Flags: bus master, fast devsel, latency 0, IRQ 255, IOMMU group 10
Memory at a3000000 (32-bit, non-prefetchable) [size=16M]
Memory at 90000000 (64-bit, prefetchable) [size=256M]
Memory at a0000000 (64-bit, prefetchable) [size=32M]
I/O ports at 5000 [disabled] [size=128]
Expansion ROM at [disabled]
Capabilities:
Kernel modules: nvidiafb, nouveau

2

I had two problems with powerdevil and controlling the brightness of an external monitor. Not the same problems as the one you describe but worth to try.

The first issue was that the controls disappeared every time I logged in, so, I had to restart the service each time using the following

systemctl --user restart plasma-powerdevil

After a Plasma update that I did recently, I the brightness control worked only for my laptop’s display and not for my external monitor. In summary, it turns out my system didn’t have the program ddcutil and that my user was not part of the i2c group. So, check if ddcutil is installed, and run the following command to get more information about the problem

ddcutil environment

If you have the same problem about your user and the i2c group, execute

sudo usermod -G i2c -a <user>

You have to log out and log in for the changes to be applied.

After that I could control the brightness of my external monitor again.

3

Thanks for your ideas. In the meantime I had already decided to try a reinstall of Kubuntu because I have my home directories on a separate partition and few additional packages installed (although I used dpkg to generate a list of installed packages to help determine the ones I particularly wanted). I particularly noticed that the packages brightness-udev and brightnessctl are no longer installed and my brightness stuff works, so I’m not really questioning any more.