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3D mode will offload rendering operations to the host gpu and therefore requires a gpu with 3D support on the host machine.

The guest side requires additional software in order to convert OpenGL commands to the raw graphics stack state (Gallium state) and channel them through virtio-gpu to the host. Currently the 'mesa' library is used for this purpose. The backend then receives the raw graphics stack state and interprets it using the virglrenderer library from the raw state into an OpenGL form, which can be executed as entirely normal OpenGL on the host machine. The host also translates shaders from the TGSI format used by Gallium into the GLSL format used by OpenGL.

Changes expected

These requirements are likely to change as VIRTIO-VULKAN is introduced.  We expect the virtual platform interface to be VULKAN based without relation to OpenGL (which will exist only in the layers above).

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 REQ-1:   The device ID MUST be set according to the requirement in chapter 5.7.1 in [VIRTIO-GPU].

 ---------- >   CHECK IF CHAPTER NUMBERS ARE VALID FOR VIRTIO 1.1

Virtqueues.

 REQ-2:   The virtqueues MUST be set up according to the requirement in chapter 5.7.2 in [VIRTIO-GPU].

        Feature bits.

 REQ-3:   The  implementation MUST set the VIRTIO_GPU_F_VIRGL flag, described in chapter 5.7.3 in [VIRTIO-GPU].

        Device configuration layout.

 REQ-4:   The implementation MUST use the device configuration layout according to chapter 5.7.4 in [VIRTIO-GPU].

      REQ-4.1: The implementation MUST use the previously reserved config structure field to report the number of capsets supported by the virglrenderer library.

           REQ-4.1.1: The implementation SHALL NOT report the value of '0' as it is treated as absence of 3D support. 

        Device Operation.

 REQ-5:   The implementation MUST support the device operation concept (the command set and the operation flow) according to chapter 5.7.6 in [VIRTIO-GPU].

      REQ-5.1: The implementation MUST support scatter-gather operations to fulfill the requirement in chapter 5.7.6.1 in [VIRTIO-GPU].

      REQ-5.2: The implementation MUST support the extended command set as described in chapter 'Virtio-GPU | Virgl3D commands' in [VIRTIO-VIRGL].

      REQ-5.3: The implementation MUST support the 3D command set as described in chapter 'VIRTIO_GPU_CMD_SUBMIT_3D' in [VIRTIO-VIRGL].

      REQ-5.4: The implementation MUST support the VIRTIO_GPU_CMD_GET_CAPSET_INFO command set as described in [??? only kernel sources as a reference so far].

      REQ-5.5: The implementation MUST support the VIRTIO_GPU_CMD_GET_CAPSET command set as described in [??? only kernel sources as a reference so far].

      REQ-5.6: The implementation SHOULD be capable  to perform DMA operations to and from client's attached resources to fulfil the requirement in chapter 5.7.6.1 in [VIRTIO-GPU] and in 'Virtio-GPU | Virgl3D commands' in [VIRTIO-VIRGL].

        VGA Compatibility.

 REQ-6:   VGA compatibility, as described in chapter 5.7.7 in [VIRTIO-GPU], is optional.

Additional features.

 REQ-7:  In addition to the command set and features, defined in [VIRTIO-GPU] and [VIRTIO-VIRGL], the implementation MAY provide:

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The solution should become more flexible and independent from third party libraries on the guest side as soon as Vulkan support is introduced. It is achieved by the fact that that Vulkan uses Standard Portable Intermediate Representation as an intermediate device-independent language, so no additional translation between the guest and the host are required. It is still work in progress [VIRTIO-VULKAN].

3.4 IOMMU Device

NOTE: The current specification draft looks quite neat except the fact that it marks many requirements as SHO

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    [VIRTIO-VIRGL]  [AN OASIS STANDARD PROPOSAL OR OWN PAPER IS NEEDED]  https://github.com/Keenuts/virtio-gpu-documentation/blob/master/src/virtio-gpu.md

    [VIRTIO-VULKAN] https://gitlab.freedesktop.org/virgl/virglrenderer/-/milestones/2

    [VIRTIO-IOMMU]  VIRTIO-IOMMU DRAFT 0.8

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