Created attachment 182013 [details]
brightness settings missing from applet and from power management settings

SUMMARY
When the screens on my PC turn off (due to Power Management settings -> Turn off Screen: 5 Minutes), *sometimes* (seemingly after the screens have been off for a longer time), the brightness controls no longer appear.

STEPS TO REPRODUCE
1. Boot with KDE in Wayland Session
2. Monitor Brightness appears in Power and Brightness widget as expected
3. Leave PC until monitors sleep - seems to be about 10 minutes, when "Turn off Screen" is set to 5min.
4. Wake PC

OBSERVED RESULT
Monitor Brightness no longer appears in the Power and Brightness widget.
Monitor Brightness is no longer a setting available in the Power Management window.
`kscreen-doctor -o` now shows both monitors as "brightness control - unsupported"

EXPECTED RESULT
I should be able to adjust monitor brightness, and monitor dimming in Power Management.
`kscreen-doctor -o` should continue to show Brightness control: supported, set to 100% and dimming to 100%.

SOFTWARE/OS VERSIONS

> Operating System: Fedora Linux 42
> KDE Plasma Version: 6.3.5
> KDE Frameworks Version: 6.14.0
> Qt Version: 6.9.0
> Kernel Version: 6.14.8-300.fc42.x86_64 (64-bit)
> Graphics Platform: Wayland
> Processors: 12 × AMD Ryzen 5 7600 6-Core Processor
> Memory: 30.5 GB of RAM
> Graphics Processor 1: AMD Radeon RX 6700 XT
> Graphics Processor 2: AMD Radeon Graphics

ADDITIONAL INFORMATION

MONITOR HARDWARE:
Primary Monitor is an HP OMEN 27Q; Secondary Monitor is an HP P22h G5.

kscreen-doctor -o, when monitor brightness is working correctly;

> Output: 1 DP-1
>         enabled
>         connected
>         priority 1
>         DisplayPort
>         Modes:  1:2560x1440@60!  2:2560x1440@165*  [... just gonna trim this]
>         Geometry: 1080,240 2560x1440
>         Scale: 1
>         Rotation: 1
>         Overscan: 0
>         Vrr: Automatic
>         RgbRange: unknown
>         HDR: disabled
>         Wide Color Gamut: disabled
>         ICC profile: none
>         Color profile source: sRGB
>         Color power preference: prefer efficiency and performance
>         Brightness control: supported, set to 100% and dimming to 100%
> Output: 2 HDMI-A-1
>         enabled
>         connected
>         priority 2
>         HDMI
>         Modes:  44:1920x1080@60*!  45:1920x1080@75  [...]
>         Geometry: 0,0 1080x1920
>         Scale: 1
>         Rotation: 8
>         Overscan: 0
>         Vrr: incapable
>         RgbRange: unknown
>         HDR: incapable
>         Wide Color Gamut: incapable
>         ICC profile: none
>         Color profile source: sRGB
>         Color power preference: prefer efficiency and performance
>         Brightness control: supported, set to 100% and dimming to 100%


kscreendoctor -o, after sleeping;
>Output: 1 DP-1
>        enabled
>        connected
>        priority 1
>        DisplayPort
>        Modes:  1:2560x1440@60!  2:2560x1440@165*  [...]
>        Geometry: 1080,240 2560x1440
>        Scale: 1
>        Rotation: 1
>        Overscan: 0
>        Vrr: Automatic
>        RgbRange: unknown
>        HDR: disabled
>        Wide Color Gamut: disabled
>        ICC profile: none
>        Color profile source: sRGB
>        Color power preference: prefer efficiency and performance
>        Brightness control: unsupported
>Output: 2 HDMI-A-1
>        enabled
>        connected
>        priority 2
>        HDMI
>        Modes:  44:1920x1080@60*!  45:1920x1080@75  [...]
>        Geometry: 0,0 1080x1920
>        Scale: 1
>        Rotation: 8
>        Overscan: 0
>        Vrr: incapable
>        RgbRange: unknown
>        HDR: incapable
>        Wide Color Gamut: incapable
>        ICC profile: none
>        Color profile source: sRGB
>        Color power preference: prefer efficiency and performance
>        Brightness control: unsupported


If I were to guess, the fact it doesn't happen immediately after sleeping would indicate it's something to do with the monitors entering some sort of sleep state of their own, and then when they 'reactivate', their brightness control settings don't get detected properly. It's plausibly related to a separate bug where windows will get moved around when waking in the same situation.

I also experienced bug https://bugs.kde.org/show_bug.cgi?id=500041, and this could plausibly be related to https://bugs.kde.org/show_bug.cgi?id=488539.

Not sure if this bug was introduced in 6.3.5, or if it's been an issue since earlier 6.3 patches.