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.
