port-amd64/57278: Fails to open console on APU+GPU AMD Crossfire system

[mikoxyzzz%gmail.com@localhost]

>Number:         57278
>Category:       port-amd64
>Synopsis:       Fails to open console on APU+GPU AMD Crossfire system
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Mar 18 20:10:00 +0000 2023
>Originator:     Miko Larsson
>Release:        9.3, current
>Organization:
>Environment:
N/A
>Description:
On a system with an APU+GPU Crossfire setup (A8 7600+Radeon R5 330), the kernel panics since it's unable to open a console. Panic is as follows (transcribed from an image, so I apologize in advance for any eventual typos), excluding log timestamps:

[drm] ib test on ring 2 succeeded in 0 usecs
[drm] ib test on ring 3 succeeded in 0 usecs
[drm] ib test on ring 4 succeeded in 0 usecs
[drm] Radeon Display Connectors
[drm] Initialized radeon 2.50.0 20080528 for radeon1 on minor 1
panic: cnopen: no console device
cpu0: Begin traceback...
vpanic() at netbsd:vpanic+0x183
panic() at netbsd:panic+0x3c
cnopen() at netbsd:cnopen+0x104
cdev_open() at netbsd:cdev_open+0x133
spec_open() at netbsd:spec_open+0x237
VOP_OPEN() at netbsd:VOP_OPEN+0x3e
vn_open() at netbsd:vn_open+0x32e
do_open() at netbsd:do_open+0xc3
do_sys_openat() at netbsd:do_sys_openat+0x74
sys_open() at netbsd:sys_open+0x24
syscall() at netbsd:syscall+0x196
--- syscall (number 5) ---
netbsd:syscall+0x196:
cpu0: End traceback...
fatal breakpoint trap in supervisor mode
trap type 1 code 0 rip 0xffffffff80235315 cs 0x8 rflags 0x202 cr2 0x74c55320fab8 ilevel 0 rsp
curlwp 0xffff89f0dbc719c0 pid 171.171 lowest kstack 0xffffa904031f02c0
Stopped in pid 171.171 (init) at        netbsd:breakpoint+0x5:  leave
breakpoint() at netbsd:breakpoint+0x5
vpanic() at netbsd+vpanic+0x183
panic() at netbsd:panic+0x3c
cnopen() at netbsd:cnopen+0x104
cdev_open() at netbsd:cdev_open+0x133
spec_open() at netbsd:spec_open+0x237
VOP_OPEN() at netbsd:VOP_OPEN+0x3e
vn_open() at netbsd:vn_open+0x32e
do_open() at netbsd:do_open+0xc3
do_sys_openat() at netbsd:do_sys_openat+0x74
sys_open() at netbsd:sys_open+0x24
syscall() at netbsd:syscall+0x196
--- syscall (number 5) ---
netbsd:syscall+0x196:
ds          8
es          0
fs          180
gs          4a70
rdi         0
rsi         ffffa9001ce4c020
rbp         ffffa904031f4ac0
rbx         0
--db_more--

At this point, the console is completely frozen and won't accept any input from e.g. the keyboard.

I've tested both 9.3 and current; on 9.3 the console completely freezes after "[drm] Initialized radeon 2.50.0 20080528 for radeon1 on minor 1", whereas on current I got the aforementioned kernel panic.
>How-To-Repeat:
1. Get ahold of a system with an identical Crossfire setup as detailed earlier
2. Try to boot NetBSD-current from e.g. an install USB
>Fix: