It will be many, many weeks before AMD supports "Clover" for their Radeon GPUs on the open-source Linux DRM / Gallium3D stack. The support they're aiming for is the Radeon HD 5000 "Evergreen" series and newer, but this Clover state tracker to support OpenCL is still a ways out for those with ATI/AMD GPUs. A whiteboard drawing of the Radeon Clover TODO list was shown at XDC2011 Chicago by John Bridgman.
John showed a whiteboard drawing of what's left to do for the open-source OpenCL support using Gallium3D Clover with modern Radeon HD graphics cards using the R600g driver. About 108 weeks it looks like, assuming no other developers contribute. On AMD's side they have Tom Stellard working on the GPGPU support
and Alex Deucher to also help. However, they haven't updated this drawing since looking at the progress made on the OpenCL state tracker
this summer via Google's Summer of Code.
Below is the drawing with rough estimates (numbers represent weeks for completion). Items scribbled out are future Radeon GPUs (e.g. Southern Islands, etc). Hopefully John Bridgman will be able to post a better image of this drawing in the Phoronix Forums.
With PathScale already having an OpenCL run-time
and a compute abstraction layer working for their PSCNV driver (their Nouveau driver fork) and this being portable to Nouveau, the open-source NVIDIA Linux driver may be the first one to bring-up OpenCL support for Gallium3D drivers.