AMD has released the Open Source driver AMDGPU with support for Radeon R9 285.
Publishing the code of this driver, the company reaches out to Linux distributions' users that have been demanding for a long time the possibility to use free drivers. The only found restriction is that Catalyst will be an additional and propietary component.
So far, to play without relinquishing the full power in Linux and taking full advantage of the possibilities of the graphics cards, licensed drivers were needed in order to have advanced features, like full support for 3D.
NVIDIA has also made a similar movement with his Nouveau project, but the performance of its free driver isn't as good as users would like it to be.
More information: Phoronix