A commit made by Marek Olšák and signed off by Alex Deucher now enables 2D tiling by default for the R600 through Cayman GPUs. The 2D color tiling mode hasn't been enabled by default (though 1D color tiling has) due to problems, but if using the latest Radeon Linux DRM driver plus Mesa 9.0+, the open-source stack should be in fairly good shape. The support on the R600 Gallium3D driver was in an experimental state for one year while the older R300 Gallium3D driver has already adequate color tiling support enabled by default.
The 2D color tiling support can continue to be manually toggled through the ColorTiling2D option within the xorg.conf configuration file.
For those unfamiliar with 2D color tiling, it's capable of delivering some OpenGL performance advantages as showcased in Using The New Radeon Gallium3D 2D Color Tiling and An Updated Look At Radeon Gallium3D 2D Color Tiling. New 2D color tiling benchmarks from the open-source Radeon driver are forthcoming.