https://bugs.kde.org/show_bug.cgi?id=482713
--- Comment #25 from matterhorn...@proton.me --- I've also had similar odd behaviour so thought I'd record it here. For more than three years using KDE on Tumbleweed I had my monitor (HP M24f 1080p) plugged into my PC via the bundled HDMI cable, and was blissfully unaware that changing the brightness of a monitor from software was even possible. Suddenly – and I forget when exactly this was, but earlier this year – I noticed that a brightness slider had appeared next to the Night Control toggle. And it worked! I assumed that a Plasma update had added either the functionality or the compatibility with my monitor. I don't remember it being only sporadically available, though I didn't use it all that much. A short while ago, maybe a month or so but no idea really, I noticed that the option was gone. And it stayed gone, so I assumed it was a regression. I didn't think to report it at the time. Now I got to wondering why it didn't work any more, did some googling, found this bug report. I yesterday switched to using a DP to HDMI cable rather than the old HDMI cable, and over the course of several reboots and logout/login cycles it doesn't seem to ever work with this cable. Weirdly, when I now switch back to the old cable, or another HDMI-HDMI cable, the brightness control seems to consistently appear. Which would imply that maybe the new DP-HDMI cable can't carry the DCC signal, something that would be entirely unsurprising – but the thing is, it is only now when I'm fiddling around with it and swapping back and forth that the brightness control appears with the HDMI-HDMI cable, whereas at least for the past few weeks I am absolutely 100% certain that it wasn't. But now I can't reproduce that. Another point is that if I swap from one cable to another during a session (i.e. the monitor is disconnected then reconnected via a different cable and port on the GPU) there are no new entries printed to the log, and the brightness slider either remains hidden or remains shown, but if I boot with HDMI-HDMI, get shown the slider, then switch to DP-HDMI, the slider is still shown but no longer has any effect (indeed, if I try to change the brightness the widget gets stuck and freezes). Should it be relevant, the cable in question is this one: https://www.amazon.de/UGREEN-DisplayPort-Uni-Direktional-Multi-Screen-Kompatibel/dp/B07V3RYBVY . It's advertised specifically as being one-way only, but at least some information must flow from the monitor to the PC as it still picks up the model name for instance. I've attached the log output of both the successful and failed cases. If I ever replicate the brightness slider failing to show with the HDMI-HDMI connection then I'll post a log of that, too. -- You are receiving this mail because: You are watching all bug changes.
