Comment 10 for bug 1938999

I could reproduce this issue on L15, when I insert DP cable, it show a lot of '*ERROR* Link Training Unsuccessful'. And from the xrandr I found the DP monitor was recognized, and I could move mouse to this external monitor, but the screen is black.

Aug 12 23:45:05 u-ThinkPad-L15-Gen-1 kernel: i915 0000:00:02.0: [drm] *ERROR* Link Training Unsuccessful
Aug 12 23:45:05 u-ThinkPad-L15-Gen-1 kernel: i915 0000:00:02.0: [drm] *ERROR* Link Training Unsuccessful

u@u-ThinkPad-L15-Gen-1:~$ uname -an
Linux u-ThinkPad-L15-Gen-1 5.11.0-25-generic #27~20.04.1-Ubuntu SMP Tue Jul 13 17:41:23 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

$ xrandr
DP-1-3 connected 1600x900+1920+0 (normal left inverted right x axis y axis) 434mm x 236mm
   1600x900 59.98*+
   1280x1024 75.02 60.02··
   1152x864 75.00··
   1024x768 75.03 60.00··
   800x600 75.00 60.32··
   640x480 75.00 59.94··
   720x400 70.08··