Laptop screen and connected 4K (DP) monitor Problem: "Battery and Brightness" in systemtray shows a different brightness-percentage than set on laptop screen. Modifying the brightness-slider then 'suddenly jumps' to a way too dark setting I need to use the hardware-keys (Fn-*) to set the brightness up again to a usable state. Still, the brightness-slider is not in sync with the OSD (OSD ~65%, brightness-slider ~45%) This was working properly already but seems to be a regression? Operating System: Fedora Linux 37 KDE Plasma Version: 5.27.5 KDE Frameworks Version: 5.106.0 Qt Version: 5.15.9 Kernel Version: 6.3.3-100.fc37.x86_64 (64-bit) Graphics Platform: Wayland Processors: 8 × Intel® Core™ i7-7820HQ CPU @ 2.90GHz Memory: 31,1 GiB of RAM Graphics Processor: Mesa Intel® HD Graphics 630 Manufacturer: LENOVO System Version: ThinkPad T470p
I also noticed that moving slider fast can get it out of sync or revert (sync) to an intermediate state. So I trust your bug report even without screenshots (: Probably backend needs some job buffering and proper ordering. I've done something like that in my personal DDC/CI brightness control app, so I should take a look at it in Plasma powerdevil too.
A possibly relevant merge request was started @ https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/3178
New merge request @ https://invent.kde.org/plasma/powerdevil/-/merge_requests/342. It fixes the brightness slider lagginess and makes the slider jump way less, still possible but negligible in practice. I have deeply pondered what this means for the slider going out of sync with the OSD. Quick testing now seems fine in terms of showing the right OSD values after quickly dragging the brightness slider. It may just all be a question of "how much time do you give powerdevil to apply the new brightness slider value before pressing the brightness key". In which case, the answer is "it needs a lot less time to apply the new brightness than it did before (but there is still a little delay theoretically)".