Well there is already a radeon_hd accelerant, but that’s only the 2D part of the driver… and as far as I know it doesn’t even initialize the 3d engine. Haiku’s native radeon_hd 2D driver was written mostly by kaliisti5 in recent years.
I’m not sure if haiku implemented what Mesa needs to run it would end up being called an accelerant (technically the same) but would probably more resemble or actually be a Linux DRM driver (direct rendering manager nothing to do with rights management) Regardless of what that part looks like end users should only care about the features the drivers provide such as APIs, and functionality HDMI , HDMI audio etc…
waddlesplash could comment on that more accurately I imagine… also he had a sort of layout as to what it would look like planned out, what we aren’t sure about yet, is what the best way to go about writing the kernel portion is from a maintanability perspective, as well as with ease of keeping up with driver updates.
The BSD’s have wrappers for Linux drivers, but they are all have one issue or anohter, such as being ugly or missing features, or being out of date. There is also a partial native Haiku to Linux wrapper that hasn’t been finished written by hamish.