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[BUG] linux-cachyos 7.3.0: HDMI monitors blank at 4K 120 Hz with VRR off (RX 9060 XT)

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
47/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
linux, shell
Domain
backend, operating-systems

Research direction

Compare the changes between linux-cachyos 7.2.10 and 7.3.0-5, focusing on kernel display support for AMDGPU and HDMI FRL/DSC at 4K 120 Hz. Reproduce with the reported RX 9060 XT setup and inspect debugfs link state during a blank; the report offers to capture it. Done means identifying and fixing the 7.3.0-5 regression so the HDMI monitors remain stable at 120 Hz.

Written by the indexing model from the issue text.

Description

Summary

After updating linux-cachyos from 7.2.10 to 7.3.0-5, two HDMI monitors running 3840x2160 at 120 Hz blank together every few minutes and come back after a moment. A third, identical monitor on DisplayPort at 160 Hz is never affected. This may be related to #1075, but the trigger looks different: VRR is set to Never, the refresh rate is 120 Hz, and amdgpu.dcfeaturemask is not set.

What isolates it
Kernel HDMI at 4K 120 Hz
linux-cachyos 7.2.10 (before update) stable
linux-cachyos 7.3.0-5 blanks repeatedly, both HDMI monitors at once
linux-cachyos 7.3.0-5 with HDMI at 60 Hz stable
linux-cachyos-lts 6.18.55 stable

Firmware (20261019), Mesa 26.2.5 and KWin 6.8.1 were the same in every row, so the kernel is the only variable. I could not test vanilla 7.3 because Arch linux is still at 7.2.11.

What the PC sees during a blank

Nothing. I watched udevadm monitor (drm), journalctl -kf filtered for amdgpu/drm, KWin's journal, and connector status/dpms in sysfs while it blanked several times. No hotplug event, no amdgpu error, no KWin output change, no connector state change. The monitors appear to lose the signal on their side while the driver believes the link is fine.

Hardware and settings
  • GPU: RX 9060 XT 16 GB (Navi 44)
  • Monitors: 3x ASUS ROG Strix XG27UCS (HDMI 2.1 with FRL up to 12 Gbps x4, DSC 1.2a, HDMI VRR 48 to 160 Hz, AMD VSDB v2)
  • HDMI-A-1 and HDMI-A-2 at 3840x2160@120, DP-1 at 3840x2160@160
  • KWin Adaptive Sync: Never on all outputs; vrr_capable and passive_vrr_capable both read 0
  • HDR off, RGB range automatic
  • Kernel cmdline: quiet nowatchdog splash rw rootflags=subvol=/@ root=UUID=... (no amdgpu parameters)
  • KDE Plasma 6.8.1 Wayland, CachyOS
Workaround

Holding linux-cachyos 7.2.10 via IgnorePkg. Happy to test a build or capture debugfs link state on 7.3 if that helps.

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Merged PRs (30d)
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