Comment # 32 on bug 1193599 from Daike Yu

I have also been bitten by this issue on a Thinkpad P15 Gen1, with a Quadro
T1000M and an i9-10885H. This issue exists on both Leap 15.4 (kernel 5.14.21)
and Tumbleweed (kernel 6.0.8).

Tested nvidia driver includes G05 (on Leap 15.4 and Tumbleweed) and G06 (on
Tumbleweed). The version of nvidia driver doesn't seem to affect the behavior.

dmesg output is almost identical to the attachment provided by Andreas earlier
(I'll attach them nonetheless).

Some observations I would like to add:

Since this issue seems to be related to the HDMI output (as indicated by the
fact that this is related to LSPCON, and other bug reports also mentioned that
HDMI is not working unless plugged in before boot up), I did some experience
with whether HDMI is working in different situations:

1. nvidia driver disabled (with prime-select), and nvidia module unloaded: HDMI
output does not work no matter HDMI cable plugged in before boot or not.

2. nvidia driver enabled (with prime-select):
  2.1. HDMI cable plugged in before boot up: HDMI output works, LSPCON error
message still appears.
  2.2. HDMI cable unplugged before boot up: HDMI output not working during X11
session. However plymouth splash does show up normally on the external monitor
after `systemctl reboot`.
  I'm guessing in this scenario the discrete GPU is providing the HDMI output.

3. nvidia driver enabled, iGPU disabled in BIOS: same as 2, except LSPCON error
messages disappeared (makes sense since i915 is not loaded at all)

Unfortunately AFAIK there's no way to disable discrete GPU only in BIOS on this
machine, so I cannot test the iGPU-only situation. If anybody know how to
disable discrete GPU on this machine please kindly let me know.

Also, on the same machine HDMI is working without flaw if I dual-boot into
Windows 10, although I'm not sure in such situation which GPU is in use (since
I don't know how to enable only the iGPU).

So I suspect there's two separate issue exists here:

1. nvidia driver is not handling HDMI hot plug correctly (therefore we need to
plug in HDMI cable before boot to get HDMI working with discrete GPU)
2. i915 have some problem with LSPCON (so HDMI output with iGPU is not working
at all).

Hope this info helps, and please let me know if there's anything else I can
help with (debug log/testing etc).