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Lock the display link

If the screen goes black after boot, or when the resolution changes, but Linux is still running (white LED, SSH works), the cause is often the link between the GPU and the HDMI converter. This page explains the cause and shows how to lock the link so it stays stable.

Not tested

This fix was reported on firmware 13.60 with the official CachyOS image, kernel 7.2.3 and a 1 TB USB SSD. It writes to debugfs, which is not a stable interface, so the path may change between kernels. Share your results on Discord.

Why it happens​

The GPU does not output HDMI directly. It sends DisplayPort (DP) to an internal DP to HDMI converter. When you pick a mode below 4K, the driver can lower the link speed. The converter then fails to sync and the screen goes black. dmesg shows the same error as in Link training error:

[drm] *ERROR* perform_8b_10b_clock_recovery_sequence: Link Training Error, could not get CR after 100 tries

A kernel that includes the fix described there needs none of this. Use this page when you can't update the kernel yet, or when the black screen comes back.

Recover without a reboot​

Try these in order. All of them need Linux to be running.

  1. Switch the TV or monitor input away and back.

  2. Switch TTY. Press Ctrl+Alt+F2, wait 2 to 3 seconds, then press Ctrl+Alt+F1. Repeat if needed.

  3. Lock the link and force a hotplug. Run both lines on the PS5 (from tty2 or over SSH):

    echo "4 0x1e" | sudo tee /sys/kernel/debug/dri/0/DP-1/link_settings
    echo 1 | sudo tee /sys/kernel/debug/dri/0/DP-1/trigger_hotplug

  4. If the screen is still black, wait for hdmi: got real edid in dmesg, then run the hotplug line a second time.

4 0x1e means four lanes at HBR3, the highest link rate. On a KDE desktop a hotplug can make KWin lose the screen, so try the TTY switch first. Gamescope is not affected.

A USB keyboard may drop out

Switching TTYs can disconnect a USB keyboard or mouse. Unplug it and plug it in again.

A service that runs before the display manager starts keeps the link locked.

Create the script:

/usr/local/bin/dp-link-lock
#!/bin/sh
f=/sys/kernel/debug/dri/0/DP-1/link_settings
mountpoint -q /sys/kernel/debug || mount -t debugfs none /sys/kernel/debug
for i in $(seq 60); do [ -e "$f" ] && break; sleep 0.5; done
echo "4 0x1e" > "$f"

Create the service:

/etc/systemd/system/dp-link-lock.service
[Unit]
Description=Lock DP-1 link to 4x HBR3 (PS5 HDMI converter)
After=systemd-modules-load.service sys-kernel-debug.mount
Before=display-manager.service

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/local/bin/dp-link-lock

[Install]
WantedBy=multi-user.target

Make the script executable and enable the service:

sudo chmod +x /usr/local/bin/dp-link-lock
sudo systemctl enable dp-link-lock

Reboot, then check the link:

cat /sys/kernel/debug/dri/0/DP-1/link_settings

The output shows Preferred: 4 0x1e when the lock is active. A few CR errors and one warning trace in dmesg during boot are normal.

Use a safe mode as well​

Keep video=DP-1:1920x1080@60 in cmdline.txt so the first mode set at boot is one every display accepts. Change the resolution from the desktop once Linux is running. See Kernel setup.