| V3D |
| === |
| |
| Mesa's ``v3d`` graphics driver stack includes a `conformant GLES3.1 |
| driver |
| <https://www.khronos.org/conformance/adopters/conformant-products/opengles#submission_882>`__ |
| called ``v3d`` and a Vulkan graphics driver called ``v3dv``, notably |
| used on the Raspberry Pi 4. |
| |
| The v3d Mesa drivers communicate directly with the `v3d |
| <https://www.kernel.org/doc/html/latest/gpu/v3d.html>`__ kernel DRM |
| driver for scheduling GPU commands. Additionally, on the Raspberry Pi |
| 4, the kernel uses the vc4 DRM driver for display support, so Mesa |
| exposes a ``vc4_dri.so`` using the kmsro helpers to do |
| behind-the-scenes buffer management between the two kernel drivers, |
| while executing rendering on the v3d kernel module. |
| |
| Initial development work was done on the Broadcom 7268 (V3D 3.3) and |
| 7278 (V3D 4.1). Development since then has been on V3D 4.2, and |
| though the 3.3 and 4.1 support continues to remain in tree, it is not |
| tested any more. Broadcom's reference software platforms do not make |
| use of the open source v3d stack, but porting a particular hardware |
| implementation to use it would still be possible. |
| |
| Hardware Documentation |
| ---------------------- |
| |
| Broadcom never released a public specification for the V3D 3.x or 4.x |
| series. |
| |
| For driver developers, Broadcom publicly released a `specification |
| <https://docs.broadcom.com/doc/12358545>`__ PDF for the 21553, which |
| is closely related to the vc4 GPU present in the Raspberry Pi. They |
| also released a `snapshot <https://docs.broadcom.com/docs/12358546>`__ |
| of a corresponding Android graphics driver. That graphics driver was |
| ported to Raspbian for a demo, but was not expected to have ongoing |
| development. |
| |
| Developers with NDA access with Broadcom or Raspberry Pi can get |
| access to the V3D architecture specification for documentation of the |
| GPU's programming model. There is also a C++ software simulator |
| called simpenrose, and the Mesa driver includes a backend |
| (``src/broadcom/drm-shim/``) to use simpenrose from an x86 system with |
| the i915 graphics driver with all of the vc4 rendering commands |
| emulated on simpenrose and memcpyed to the real GPU. Note that |
| simpenrose's API drifts over time, so you need to be syned up with |
| whatever version Mesa was last being developed against. |