There's been work going on for years of "soft" FP64 support to allow emulated support for the double-precision floating-point data types for GPUs not otherwise inherently supporting this capability. The soft support would allow for some older GPUs to then advertise OpenGL 4.0+ support now that ARB_gpu_shader_fp64 support could be enabled. That day looks like it's finally coming for mainline Mesa.

David Airlie who continues investing a bit of time in improving the R600 Gallium3D driver is positioning the soft FP64 support for upstream soon. This would really help the Radeon HD 5000/6000 series hardware sans the HD 5800/6900 series that have native FP64 support exposed currently and thus at OpenGL 4.3+ support right now with this open-source AMD driver. The FP64 / ARB_gpu_shader_fp64 support is a requirement for OpenGL 4.0 compliance.

David started off this week by posting some precursor patches to FP64 for Mesa. He commented, "I've been fixing up Elie's work and although the produced shaders are large, and really show up the copy prop and sb liveness passes as horrible inefficent when you have lots of if statements, I think we should start angling towards upstreaming it."

The good news is most (any?) games don't rely upon FP64 so if there is slow emulated performance it shouldn't matter much but just crosses the remaining item off the list for being able to enable OpenGL 4.x support. Airlie also noted that with the soft FP64 support the R600g driver is up to passing 99% of the Piglit regression tests.

Here's to hoping that soft FP64 support will finally make it into mainline for the Mesa 18.1 release next quarter.