port-amd64/59756: NetBSD 10.1 UEFI bootloader does not work on ASRock Rack B650D4U mainboard with EPYC 4005 series CPU

[bernd.sieker%posteo.net@localhost]

>Number:         59756
>Category:       port-amd64
>Synopsis:       NetBSD 10.1 UEFI bootloader does not work on ASRock Rack B650D4U mainboard with EPYC 4005 series CPU
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Nov 13 13:40:00 +0000 2025
>Originator:     bernd.sieker%posteo.net@localhost
>Release:        NetBSD 10.1
>Organization:
>Environment:
System: NetBSD fluor.bersie.home 10.1 NetBSD 10.1 (FLUOR) #38: Tue Jan 21 08:19:05 CET 2025 bernd%fluor.bersie.home@localhost:/usr/src/sys/arch/amd64/compile/FLUOR amd64
Architecture: x86_64
Machine: amd64
>Description:
The system is an ASRock Rack B650D4U server mainboard with an AMD
EPYC 4465P CPU and two M.2 nvme SSDs.

I have used gpt to create EFI system partitions on both SSDs of
various sizes (64M to 640M) tried formatting FAT16 or FAT32, mounted
it with or without long names enabled, created the efi/boot folder
and copied bootx64.efi from /usr/mdec into it.

Whenever the system is set to UEFI boot, only a blank screen with
a cursor on the upper left is shown.

The machine can boot other uefi bootloaders just fine, I tested
rEFInd in various configurations.

I also tried using an older version of NetBSD's bootx64.efi from
a system I installed in 2021, with the same result. Either version
of that bootloader worked fine on Dell T110, Dell T320 and Dell
T420 systems with different Intel Xeon CPUs.

I also tried rEFInd to load the NetBSD bootloader, with the same
result (blank screen, cursor in the top left).

I tested BIOS versions 21.08 and 22.03 (all new) on the
mainboard.

The USB install image (self-built on another amd64 system, as well
as directly downloaded from netbsd.org) exhibits the same behaviour.

The problem appears to be the combination of this ASRock Rack
mainboard and/or AMD CPU with the NetBSD uefi bootloader.

The NetBSD bootloader works fine with the Dell/Xeon systems, and
the ASRock/AMD system boots fine with rEFInd.

I don't know if other CPUs will work on this mainboard.

Legacy booting works without problems and the systems runs just
fine.

>How-To-Repeat:
Install efi boot partition with NetBSD's bootx64.efi on ASRock Rack
B650D4U mainboard with EPYC 4005 series CPU. Reboot system in UEFI
mode, observe hanging bootloader.
>Fix:
Fix is unknown to me. Workaround is to boot in legacy ("BIOS") mode.