Hello. I am reporting a regression in the kernel. an external HDMI monitor fails to wake up from a low-power state. The issue occurs both in the VT console (using consoleblank parameter) and in the X.Org graphical session (using xset dpms force off). The internal laptop display resumes correctly. This problem was not present in Linux kernel 6.17. It started occurring after updating to kernel 6.18.0. My Kernel: 6.18.3, built from vanilla sources in Gentoo. Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Strix [Radeon 880M / 890M] (rev c4).
No messages in dmesg regarding this. Steps to Reproduce: 1. Connect an external monitor via HDMI. 2. Boot with the kernel parameter consoleblank=30. 3. Wait 30 seconds for the screen to blank and some time (no more than 5 mins) additionally. 4. Try to wake the display by pressing a key. The external monitor remains off, while the internal laptop display turns on. 5. Also reproducible in X11/Xorg session using xset dpms force off. It is also needed to spent some time in off state. Thank you.
