Support was added to existing drivers for similar hardware, a number of commits mention the Milk-V Pioneer board, I can't comment on how well it is supported, though:
Thanks - I was grepping through the kernel sources and could not find any references to the Pioneer, Milk-V or the SG2042 SoC. It makes sense it's mentions in the commit logs instead, especially if the hardware is rather similar to existing supported components... I didn't know about the freshbsd site, nice to have this!
Yeah, freshbsd.org is useful for linking to searches publicly, I seem to recall GitHub requiring you to be logged in.
Likely works fine in UEFI boards, using sbi for uart and timers, as long as the rest of the hardware is relatively standard.