RADV ACO Back-End Begins Tackling Navi 2 / GFX10.3 Support

With the "Sienna Cichlid" and "Navy Flounder" open-source driver support as what appear to be the first "Navi 2" GPUs and the first of the "GFX10.3" generation on the graphics engine side there is the initial kernel support with Linux 5.9 and the initial Mesa support for 20.2. That Mesa support has been focused on RadeonSI as the official OpenGL driver as well as Mesa's RADV driver as the Radeon Vulkan driver in-tree but not officially supported by AMD. That RADV support is currently un-tested. Both drivers currently depend upon the "AMDGPU" back-end found in the forthcoming LLVM 11.0 with its initial GFX10.3 support. But now on the RADV driver side there is preliminary GFX10.3 bits landing for the popular "ACO" back-end.

ACO is the back-end worked on by Valve and other stakeholders like open-source graphics driver engineers from Google and Red Hat. But as ACO isn't officially supported by AMD, there hasn't been any patches from them in wiring up the Navi 2 / GFX10.3 support for this AMDGPU LLVM alternative. Rhys Perry as part of Valve's Linux driver efforts though has worked out what should be the initial changes needed for this yet-to-be-released hardware with ACO.

From the shader compiler perspective the necessary changes can be looked at from the GFX10.3 enablement patches that were merged into LLVM. But as Rhys notes with the patches, given the lack of hardware availability to these developers there hasn't been any actual testing yet. "fossil-db compiles and disassembles without issues, but otherwise there's basically no testing."

These initial changes for ACO with GFX10.3 will come with Mesa 20.2 but more than likely there will be more fixes and optimizations to find out of Mesa 20.3 later in the year given the lack of real testing so far and the eventual performance improvements once the code can be tuned for the new hardware.