booters on real risc-v hardware?

["T K Spindler (moof)" <dogcow%babymeat.com@localhost>]

The other day I received a Milk-V Duo 256M SBC; it uses a Sophgo SG2002
(a C906 core, and a derivative of the CV1800B chip), and uses OpenSBI
and u-boot (and some other glue) to boot linux on its primary core. (It
also as a secondary C906, and a ARM A53; not bad for $10 + shipping.)

While linux is all well and good, I'd like to attempt to boot NetBSD on
it, which begs the question - what booter *should* it be using? Ought it
to use u-boot (and all that entails), or hook into OpenSBI, or use some
other methodology?

While FreeBSD notes that it *can* use OpenSBI, it is unclear whether
this has actually been tried on real hardware or not.

If any of y'all are curious as to how the vendor of the board I've got
does it, https://github.com/milkv-duo/duo-buildroot-sdk/ is their build
system.