kern/56648: i915drmkms fails to detect output

[manu%netbsd.org@localhost]

>Number:         56648
>Category:       kern
>Synopsis:       i915drmkms fails to detect output
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jan 21 02:15:01 +0000 2022
>Originator:     Emmanuel Dreyfus
>Release:        NetBSD-current/amd64
>Organization:
NetBSD
>Environment:
System: NetBSD basalte 9.99.93 NetBSD 9.99.93 (GENERIC) #94: Fri Jan  7 03:55:44 CET 2022  manu@basalte:/home2/manu/netbsd-src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:
The machine is a notebook with Intel UHD Graphis 615. It features an internal dispay (eDP1) and an external HDMI output.

Since the recent DRM update, the integrated dispaly now works with i195drmkms, but it fails to detect a display conenced on the external HDMI output. xrandr says:
# xrandr -d :0
Screen 0: minimum 8 x 8, current 1920 x 1200, maximum 32767 x 32767
eDP1 connected primary 1920x1200+0+0 left (normal left inverted right x axis y axis) 90mm x 150mm
   1200x1920     55.00*+
   DP1 disconnected (normal left inverted right x axis y axis)
   HDMI1 disconnected (normal left inverted right x axis y axis)
   HDMI2 disconnected (normal left inverted right x axis y axis)
   VIRTUAL1 disconnected (normal left inverted right x axis y axis)

   When booting (UEFI mode) the external display works and automatically mirrors the integrated display. It gets blank when i915drmkms takes over the display during boot time.
>How-To-Repeat:
 Use the machine :-/
>Fix:
 Not known yet