R600g "Soft" FP64 Shows Signs Of Life, Enabling Older GPUs To Have OpenGL 4 In 2018

Most pre-GCN AMD graphics cards are still limited to OpenGL 3.3 support at this time due to not supporting FP64. Only the HD 5800/6900 series on R600g currently have real double-precision floating-point support working right now so at present they are on OpenGL 4.3 rather than 3.3, but those other generations may be catching up soon thanks to the "soft" FP64 code.

There's been soft/emulated FP64 support worked on and off over the years for R600g with ARB_gpu_shader_fp64 being the major extension not handled by most of the GPUs on the R600g driver. Once that "soft" support is in place along with the related ARB_vertex_attrib_64bit extension, it's possible most R600g supported hardware could catch-up to OpenGL 4.3 like the HD 5800/6900 series.

It's been a while since last having anything to report on this initiative but David Airlie has commented, "softfp64 is trickling along. I just knocked over min/max support today."

The latest R600g soft FP64 support can be found via this Mesa branch. It's not going to be merged in time for Mesa 18.0, but perhaps for Mesa 18.1 or 18.2 we will see the support all squared away for breathing some new life into this vintage Radeon graphics cards.

Related, hitting Mesa 18.0 Git yesterday was ARB_enhanced_layouts for R600g. That just leaves ARB_query_buffer_object left before R600g can expose OpenGL 4.4 support, assuming the driver can pass the OpenGL CTS. This is all good news if you're still stuck on the R600g driver in 2018.