Bug 496859

Hello,

Environment:
- Hardware: XMG Core 16 with NVIDIA RTX 4060 Mobile GPU and AMD iGPU
- Operating System: Arch Linux (up to date)
- Display Server: Wayland
- KDE Plasma: 6.2.4
- PowerDevil: 6.2.4-1

Issue:
The KDE brightness slider is not functional. When trying to adjust brightness using the GUI slider, no actual brightness change occurs. The system log shows repeated messages "ignoring brightness change, it's coming from the applet itself".

Steps to Reproduce:
1. Boot system
2. Try to adjust brightness using the KDE brightness slider
3. Observe that the slider moves but has no effect on screen brightness

Expected Behavior:
Moving the brightness slider should change the screen brightness.

Actual Behavior:
- The slider moves but does not affect brightness
- System logs show "ignoring brightness change, it's coming from the applet itself"
- PowerDevil logs show "Failed to initialize callback"

Workaround:
Brightness can be successfully controlled using the command line tool 'brightnessctl', confirming that hardware brightness control is working properly.

Relevant Log Output:
Nov 30 11:53:34 archlinux systemd[1]: Created slice Slice /system/systemd-backlight.
Nov 30 11:53:34 archlinux systemd[1]: Starting Load/Save Screen Backlight Brightness of backlight:acpi_video0...
Nov 30 11:53:34 archlinux systemd[1]: Starting Load/Save Screen Backlight Brightness of backlight:amdgpu_bl2...
Nov 30 11:53:34 archlinux systemd[1]: Finished Load/Save Screen Backlight Brightness of backlight:acpi_video0.
Nov 30 11:53:34 archlinux systemd[1]: Finished Load/Save Screen Backlight Brightness of backlight:amdgpu_bl2.
Nov 30 11:53:35 archlinux systemd[1]: Starting Set backlight permissions...
Nov 30 11:53:35 archlinux systemd[1]: backlight-permissions.service: Deactivated successfully.
Nov 30 11:53:35 archlinux systemd[1]: Finished Set backlight permissions.
Nov 30 11:53:43 archlinux systemd[828]: Starting Powerdevil...
Nov 30 11:53:44 archlinux org_kde_powerdevil[1226]: Initializing libddcutil.  ddcutil version: 2.1.4, shared library: /usr/lib/libddcutil.so.5.1.2
Nov 30 11:53:44 archlinux org_kde_powerdevil[1226]: Options passed from client:
Nov 30 11:53:44 archlinux org_kde_powerdevil[1226]: Applying combined options:
Nov 30 11:53:44 archlinux org_kde_powerdevil[1226]: Library initialization complete.
Nov 30 11:53:44 archlinux org_kde_powerdevil[1226]: org.kde.powerdevil: [DDCutilDetector]: Failed to initialize callback
Nov 30 11:53:44 archlinux systemd[1]: Created slice Slice /system/dbus-:1.1-org.kde.powerdevil.discretegpuhelper.
Nov 30 11:53:44 archlinux systemd[1]: Started dbus-:1.1-org.kde.powerdevil.discretegpuhelper@0.service.
Nov 30 11:53:44 archlinux systemd[1]: Created slice Slice /system/dbus-:1.1-org.kde.powerdevil.chargethresholdhelper.
Nov 30 11:53:44 archlinux systemd[1]: Started dbus-:1.1-org.kde.powerdevil.chargethresholdhelper@0.service.
Nov 30 11:53:44 archlinux systemd[1]: Created slice Slice /system/dbus-:1.1-org.kde.powerdevil.backlighthelper.
Nov 30 11:53:44 archlinux systemd[1]: Started dbus-:1.1-org.kde.powerdevil.backlighthelper@0.service.
Nov 30 11:53:44 archlinux org_kde_powerdevil[1226]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
Nov 30 11:53:44 archlinux systemd[828]: Started Powerdevil.
Nov 30 11:53:44 archlinux org_kde_powerdevil[1226]: org.kde.powerdevil: Handle button events action could not check for screen configuration
Nov 30 11:53:44 archlinux org_kde_powerdevil[1226]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
Nov 30 11:53:44 archlinux kclockd[1457]: PowerDevil found, using it for time tracking.
Nov 30 11:53:53 archlinux systemd[1]: dbus-:1.1-org.kde.powerdevil.discretegpuhelper@0.service: Deactivated successfully.
Nov 30 11:53:54 archlinux systemd[1]: dbus-:1.1-org.kde.powerdevil.chargethresholdhelper@0.service: Deactivated successfully.
Nov 30 11:53:54 archlinux systemd[1]: dbus-:1.1-org.kde.powerdevil.backlighthelper@0.service: Deactivated successfully.
Nov 30 11:54:22 archlinux systemd[1]: Started dbus-:1.1-org.kde.powerdevil.backlighthelper@1.service.
Nov 30 11:54:32 archlinux systemd[1]: dbus-:1.1-org.kde.powerdevil.backlighthelper@1.service: Deactivated successfully.
Nov 30 11:56:14 archlinux systemd[1]: Started dbus-:1.1-org.kde.powerdevil.backlighthelper@2.service.
Nov 30 11:56:24 archlinux systemd[1]: dbus-:1.1-org.kde.powerdevil.backlighthelper@2.service: Deactivated successfully.
Nov 30 12:01:59 archlinux systemd[1]: Started dbus-:1.1-org.kde.powerdevil.backlighthelper@3.service.

Additional Information:
- The system has two backlight devices: acpi_video0 and amdgpu_bl2
- Proper permissions are set (user is in video group)
- Manual brightness control through /sys/class/backlight/amdgpu_bl2/brightness works with sudo
- This appears to be a specific issue with PowerDevil's backlight handling on AMD GPUs under Wayland

Please let me know if you need any additional information to investigate this issue.

I would really appreciate support on this issue.

Kind regards.