Doesn't the UEFI firmware map a GPU framebuffer into the main address space "for free" so you can easily poke raw pixels over the bus? Then again the UEFI FB is only single-buffered, so if you rely on that in lieu of full-fat GPU drivers then you'd probably want to layer some CPU framebuffers on top anyway.

Yes if you have UEFI.

well, if you poke framebuffer pixels directly you might as well do scanline racing.