kern/56677: radeon firmware cannot load with root on zfs

[oskar%fessel.org@localhost]

>Number:         56677
>Category:       kern
>Synopsis:       radeon firmware cannot load with root on zfs
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Jan 29 23:30:00 +0000 2022
>Originator:     Jan-hinrich Fessel
>Release:        -current
>Organization:
>Environment:
NetBSD zippo.fessel.org 9.99.93 NetBSD 9.99.93 (ZAPPA) #0: Sat Jan 22 00:01:59 CET 2022  root@:/var/obj/sys/arch/amd64/compile/ZAPPA amd64

>Description:
Using the setup described at https://wiki.netbsd.org/wiki/RootOnZFS/ the kernel panics during load with an ATI FirePro 2270 x1 as the console device and radeon* enabled.

(handwritten transcript)
kern info: [drm] Loading CEDAR Microcode
r600_cp: Failed to load firmware "radeon/CEDAR_pfp.bin"
{drm:netbsd:evergreen_inot+0x374} *ERROR* Failed to load fi...

radeon0: error: Fatal error during GPU init
radeon0: unable to register drm: 2
panic: chosen: no console device

I also built a custom Ramdisk with the firmware on it at /usr/libdata/firmware/radeon, but that did not change anything.

When not booting to the ifs root, the card works, but without acceleration.  
kern info: [drm] ring test on 0 succeeded in 1 usecs
kern error: [drm:(/hurz/src/sys/external/bsd/drm2/dist/drm/radeon/radeon_r600_dma.c:274)r600_dma_ring_test] *ERROR* radeon: ring 3 test failed (0xCAFEDEAD)
radeon0: autoconfiguration error: error: disabling GPU acceleration

>How-To-Repeat:
follow the instructions at https://wiki.netbsd.org/wiki/RootOnZFS/ with an ATI Radeon installed as console device.  Probably with any card that loads microcode from the filesystem.
While at it, find that the system cannot dump core...

>Fix: