Update: this is an intermittent timing race. Three consecutive boots on
the same kernel (7.0.0-22.22-generic) show the failure tracks exactly
how late the xe display driver loads relative to the Thunderbolt DP-
tunnel setup/teardown:
Boot A (original report):
[t+17s] thunderbolt 0000:00:0d.2: 0:5 <-> 1:14 (DP): not active, tearing down
[t+101s] xe 0000:00:02.0: [drm] Found pantherlake ... integrated display
-> tunnel torn down 84s before xe loads; external monitor dead until I
manually
unplug/replug the Thunderbolt cable. systemd-analyze blame shows a ~99s
udev
coldplug stall this boot (dev-rfkill, tpm0, ttyS0-3 settling at ~1m39s).
Boot B:
[t+17s] thunderbolt ... (DP): not active, tearing down
[t+26s] xe ... Found pantherlake ... integrated display
-> same teardown, but xe came up ~9s later and the DP tunnel re-established
automatically; monitor worked.
Boot C:
[t+16s] xe ... Found pantherlake ... integrated display
[t+32s] thunderbolt 0-1: new device found (dock)
-> xe already up before the dock's DP tunnel was negotiated; no teardown;
clean.
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https://bugs.launchpad.net/bugs/2155195
Title:
[Panther Lake/xe] DisplayPort-over-Thunderbolt external monitor not
detected at cold boot (regression in linux 7.0.0-22)
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