Raspberry Pi VC4 Graphics Driver Working To Support QPU Shaders

The latest Raspberry Pi graphics driver hacking by Eric Anholt of Broadcom has been working to support QPU shaders by this open-source driver stack. QPUs are the shader core of the graphics hardware found in the Raspberry Pi SoC, but come up short of supporting OpenCL or OpenGL compute shaders.

QPU shaders aren't suitable enough for handling OpenGL compute shaders or OpenCL for GPGPU, but does allow writing QPU shaders in raw assembly for execution on these shader cores. Anholt hasn't been working on supporting QPU shaders via the open-source VC4 driver stack due to these limitations plus there are security implications too since the lack of an MMU allows the GPU shader programs to access anywhere in system memory.

Eric is looking at supporting QPU shaders now though with this open-source driver stack since it can be used for accelerated video decode. For now he's pursuing an approach where there is root-only execution of the QPU shaders due to lack of validation support. He's got an experimental implementation currently running in his kernel tree and is looking like this support might come to the VC4 DRM driver with the Linux 4.10 kernel.

Those interested in more information can read this blog post.