| 1 | V3D
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| 2 | ===
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| 3 |
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| 4 | Mesa's V3D graphics driver stack includes a `conformant GLES3.1
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| 5 | driver
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| 6 | <https://www.khronos.org/conformance/adopters/conformant-products/opengles#submission_882>`__
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| 7 | called V3D and a Vulkan graphics driver called V3DV, notably
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| 8 | used on the Raspberry Pi 4 and Raspberry Pi 5.
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| 9 |
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| 10 | The V3D Mesa drivers communicate directly with the `V3D
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| 11 | <https://www.kernel.org/doc/html/latest/gpu/v3d.html>`__ kernel DRM
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| 12 | driver for scheduling GPU commands. Additionally, on the Raspberry Pi
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| 13 | 4 and 5, the kernel uses the VC4 DRM driver for display support, so Mesa
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| 14 | exposes a ``vc4_dri.so`` using the kmsro helpers to do
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| 15 | behind-the-scenes buffer management between the two kernel drivers,
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| 16 | while executing rendering on the V3D kernel module.
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| 17 |
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| 18 | Initial development work was done on the Broadcom 7268 (V3D 3.3) and
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| 19 | 7278 (V3D 4.1). Development since then has been on V3D 4.2 (Raspberry
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| 20 | Pi 4), and V3D 7.1 (Raspberry Pi 5). When the support for V3D 7.1
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| 21 | landed, the support for 3.3 and 4.1 was dropped as it was not tested
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| 22 | anymore (see `MR#25851
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| 23 | <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25851>`__)
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| 24 | Broadcom's reference software platforms do not make use of the open
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| 25 | source V3D stack, but porting a particular hardware implementation to
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| 26 | use it would still be possible.
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| 27 |
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| 28 | Hardware Documentation
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| 29 | ----------------------
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| 30 |
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| 31 | Broadcom never released a public specification for the V3D 3.x or 4.x
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| 32 | series.
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| 33 |
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| 34 | For driver developers, Broadcom publicly released a `specification
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| 35 | <https://docs.broadcom.com/doc/12358545>`__ PDF for the 21553, which
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| 36 | is closely related to the VC4 GPU present in the Raspberry Pi. They
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| 37 | also released a `snapshot <https://docs.broadcom.com/docs/12358546>`__
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| 38 | of a corresponding Android graphics driver. That graphics driver was
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| 39 | ported to Raspbian for a demo, but was not expected to have ongoing
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| 40 | development.
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| 41 |
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| 42 | Developers with NDA access with Broadcom or Raspberry Pi can get
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| 43 | access to the V3D architecture specification for documentation of the
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| 44 | GPU's programming model. There is also a C++ software simulator
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| 45 | called simpenrose, and the Mesa driver includes a backend
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| 46 | (``src/broadcom/drm-shim/``) to use simpenrose from an x86 system with
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| 47 | the i915 graphics driver with all of the VC4 rendering commands
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| 48 | emulated on simpenrose and memcpyed to the real GPU. Note that
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| 49 | simpenrose's API drifts over time, so you need to be synced up with
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| 50 | whatever version Mesa was last being developed against.
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