linux-kernel - External HDMI monitor fails to wake up from DPMS/consoleblank since kernel 6.18

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Message-ID: <zeo54utdQP5v8eYapWyEEqMIAIVyazyK360IARqaw91yEK75U_c7NHDmchrX_XG5irs3AJ9m-ytSXUXsS2Z4Awh1BzBR9HfwHW7a9e1uKgg=@proton.me>
Date: Wed, 07 Jan 2026 17:31:03 +0000
From: alliancetrooper <alliancetrooper@...ton.me>
To: "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Cc: "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: External HDMI monitor fails to wake up from DPMS/consoleblank since kernel 6.18

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.