Radeon R600g Driver Adds Experimental Support For Rusticl

While there is already RadeonSI driver support for the Rust OpenCL "Rusticl" implementation in Mesa since v23.1, merged now for Mesa 23.2 is experimental support for Rusticl with the older Radeon R600g for pre-GCN graphics cards.

AMD's official OpenCL compute stack with ROCm only supports newer generations of GPUs while Mesa's older "Clover" OpenCL Gallium3d state tracker has long supported the R600g driver but lacking OpenCL image support and other limitations. The new OpenCL solution within Mesa that has come together nicely over the past year is Rusticl that is written in the Rust programming language.

Rusticl has supported the RadeonSI driver and the other major Mesa drivers while now Gert Wollny has added experimental support for the R600g driver. Gert noted in the now-merged merge request:

"The MR adds some support for global_load and global_store, it only can deal with up to vec4 float or vec2 double values, and images are not supported at all - I think r600 on Clover also doesn't support these. AFAICS the problem there doesn't lie in the shader, but in the image state set-up.

Enabling the backend still needs export RUSTICL_ENABLE=r600"

So with Mesa 23.2 when building with Rusticl support and using the "RUSTICL_ENABLE=r600" environment variable, it's now possible to use this modern OpenCL implementation with AMD Radeon HD 6000 series graphics cards and older. But sadly still lacking OpenCL image support for now and will be interesting to see how performant it is and ultimately how well it matures moving ahead.