AMD Radeon RX 6500 XT crash after reboot following fw_update

Hi,

I'm trying to setup OpenBSD 7.8 (release) on a AMD Ryzen 5 system (GPU: 
AMD Radeon RX 6500 XT). The installation went without errors, but when 
I ran

	# fw_update

(which didn't report any errors, and added amdgpu and a number of
related drivers) and rebooted, I got the following kernel panic (OCRed
from the photo):

=======================================================================
016 pledge_sysctl	017_tmppath		018 pledgepaths
019_unveil_mount	020_freetype		021_calendar
022_recvfd		023_calendar		024_expat
025_sack		026_smtpd		027_iked
028_xserver		029_v6daemons		030_rpki
starting local daemons: cron xenodm.
Wed Apr 15 17:15:59 CEST 2026
drm_sched_entity_init: called with uninitialized scheduler
drm_sched_entity_init: called with uninitialized scheduler
drm:pid7964: drm_sched_job_init *ERROR* [drm] *ERROR* drm_sched_job_init: entity has no rq!
uvm_fault(0xfffffd83dd97e2e8, 0x1f0, 0, 1) -> e
kernel: page fault trap, code=0
Stopped at	amdgpu_bo_unreserve+0x1a:	movq	0x1f0(%rdi), %rdi
    TID    PID    UID     PRFLAGS     PFLAGS  CPU  COMMAND
*386028   7964      0    0x100000          0    4K Xorg
 294895  72157      0    0x100002          0    2  sha256
amdgpu_bo_unreserve (0) at amdgpu_bo_unreserve+0x1a
amdgpu_vm_init(ffff8000001f0000.ffff800001838000, 0) at amdgpu_vm_init+0x440
amdgpu_driver_open_kms(ffff8000001f0058,ffff8000022d5800) at amdgpu_driver_open_kms+0x139
drm_file_alloc(ffff8000001ae980) at drm_file_alloc+0x22d
drmopen(15701,3,2000,ffff8000fffeafe0) at drmopen+0x12c
spec_open_clone(ffff80005e870218) at spec_open_clone+0x166
spec_open(ffff80005e870218) at spec_open+0x198
VOP_OPEN(fffffd83d822cbf8,3,fffffd845d6c6bc8,ffff8000fffeafe0) at VOP_OPEN+0x57
vn_open(ffff80005e870430,3,0) at vn_open+0x2ea
doopenat(ffff8000fffeafe0,ffffff9c,73a981fa4c40,2,0,ffff80005e8705d0) at doopenat+0x221
syscall(ffff80005e870650) at syscall+0x5f9
Xsyscall at Xsyscall+0x128
end of kernel
end trace frame: 0x73a981fa4c20, count: 3
https://www.openbsd.org/ddb.html describes the minimum info required in bug
reports. Insufficient info makes it difficult to find and fix bugs.
ddb{4}>
=======================================================================

Next, at the ddb prompt I entered

	ddb{4}> reboot

and tried to enter UKC to "disable amdgpu", entering "boot -c" at the
initial "boot>" prompt, but then I got the following screen:

=======================================================================
kbc: cmd word write error
[ using 4604312 bytes of bsd ELF symbol table ]
Copyright (c) 1982, 1986, 1989, 1991, 1993
        The Regents of the University of California.  All rights reserved.
Copyright (c) 1995-2025 OpenBSD. All rights reserved.  https://www.OpenBSD.org

OpenBSD 7.8 (GENERIC.MP) #54: Sun Oct 12 12:58:11 MDT 2025
    [email protected]:/usr/src/sys/arch/amd64/compile/GENERIC.MP
real mem = 16223113216 (15471MB)
avail mem = 15704649728 (14977MB)
User Kernel Config
UKC>
=======================================================================

and the keyboard was unresponsive (at the same time, cursor after the 
"UKC>" prompt is flickering like crazy).

Any help would be appreciated.