support for the Picasso APU in amdgpu

[Bakul Shah]

I recenty bought a relatively inexpensiven Ryzen 5 3500U
laptop & FreeBSD-12.1 came up just fine.  Except for a couple
of things, one of them being graphics.

I installed drm-kmod (drm-fbsd12.0-kmod-4.16.g20200115 &
drm-kmod-g20190710) and also xf86-video-amdgpu-19.0.1.  I see
/dev/drm/ but Xorg terminates as /dev/dri doesn't exist.

Looks like support for this particular AMD mobile chip
(Picasso series) is missing.

Files in kms-drm-f3206bf/drivers/gpu/drm/amd/amdgpu seem
pretty much copies of linux versions. Is f3206bf a linux
source tag? Were the sources converted using a script or
manually?

Linux seem to have added Picasso support in 4.20.  Grepping
shows very few changes (as Picasso is basically RavenRidge).

I can do one of two things: either make the few source changes
to the existing drm package or try to upgrade to 4.20 -- the
latter seems like a bigger task.

On the wiki.freebsd.org/Graphics I see that updating drm-devel
to 4.20 is 20% complete but I suspect this page is outdated!
Looking at drm-deel-kmod/Makefile it seems it is based on
linux 5.0? Ideally I don't want to upgrade to -current.

Any advice?

Thanks,
Bakul