While AMD has their open-source Linux driver stack, their GPU's BIOS hasn't been open-source though in years prior there was talk of reverse-engineering the ATI BIOS. That project didn't pan out but now there's a new developer claiming to have an open-source video BIOS for Radeon hardware.
His claim was made in our forums and he cites his SourceForge.net OpenRadeonBIOS project page.
At the moment there's one file (vbios0.0.7z) from yesterday. In digging through the source to this supposed Radeon BIOS, there's a mix of old and new code, including VBE code from more than one decade ago.
Supposedly this open-source BIOS will work with Windows XP and then under Linux can work using the open-source Radeon driver at least for CentOS and Lubuntu. However, it seems only VGA connections are supported (no HDMI/DVI/DP) and there's likely a host of other limitations.
The README also doesn't say which Radeon GPUs are actually supported. However, for those wanting to dig deeper into this new open-source Radeon GPU BIOS project, hit up the links above.