Thread for bug #422455:

I recently bought an 1080p / 144 Hz Viewsonic monitor which I run on my AMD Radeon (amdgpu) card. I noticed that when using a DisplayPort cable rather than a HDMI one, the monitor refuses to go or stay into standby making it impossible to use this essential power saving feature. I was convinced this is a Kernel or driver issue and discussed it on generic Linux forums. Someone then suggested I try putting the monitor in standby in an IceWM session, which to my surprise works perfectly, revealing the bug lies with KDE most likely its PowerDevil module. Here's a list of the exact results I get with each session:

• IceWM: Tested with 'xset dpms force standby'. Monitor properly goes into standby, resumes only once a key is pressed or the mouse is moved.
• Plasma (X11): Tested with 'xset dpms force standby'. Monitor goes into standby but only stays there for about 3 seconds, powering on afterward despite not moving the mouse or pressing any key.
• Plasma (Wayland): Tested with a 1 minute timeout from System Settings due to lack of alternative to xset for triggering standby on demand. Monitor goes powers down for roughly 3 seconds, after which it powers back on and reveals the login screen (the session crashes, see bug #420160 for this aspect).

It should be reiterated that my monitor properly handles energy saving on both the X11 and Wayland Plasma sessions when using a HDMI cable, this only happens over DisplayPort. I have to use DP due to HDMI only supporting up to 120 Hz of the 144 Hz allowed by the monitor. Currently I have to trade the ability to put the screen in standby, which results in extra electricity consumption as well as wearing the monitor out more rapidly. As my above test indicates the issue is KDE related, I hope we can find out what it is and have it fixed for the next Plasma release if possible.