re: kern/56714: Radeon acceleration not working with SAPPHIRE AMD FIREPRO 2270 x1

[matthew green <mrg%eterna.com.au@localhost>]

this is also the same problem that triggers PR#57059, which has
a teardown issue that causes a panic afterwards.


> 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)

we've recently made some progresss in understanding this problem.

it appears to happen on UEFI boots only.  at least 3 people have
confirmed this fixes (or breaks) their systems.

in confirmed i was able to break it on my ryzen 3600 system by
turning on uefi.  this systems normally runs with a serial console
(which is not supported by the uefi on the host, hence using bios
normally), so as part of the effort to debug this i forced the
kernel to use serial console using these options:

options         CONS_OVERRIDE
options         CONSDEVNAME="\"com\""
options         CONSPEED=115200
options         CONADDR=0x3f8

(note that previously, CONS_OVERRIDE was not required.)

however, this kernel boots from UEFI and *does* have working
radeon acceleration.  eg:

Dec  2 08:11:57 the-blessing /netbsd: [  24.6873761] {drm:netbsd:r600_dma_ring_test+0x22c} *ERROR* radeon: ring 3 test failed (0xCAFEDEAD) after 100000 usecs

vs

Dec  2 08:53:42 the-blessing /netbsd: [ 2057.8790796] [drm] ring test on 3 succeeded in 2 usecs


hopefully this data point can help isolate the cause.


.mrg.