# PowerVR

PowerVR is an open source Vulkan driver for Imagination Technologies PowerVR GPUs, starting with those based on the Rogue architecture.

The driver is conformant to Vulkan 1.0 on BXS-4-64, but not yet on other GPUs and Vulkan versions, so it requires exporting `PVR_I_WANT_A_BROKEN_VULKAN_DRIVER=1` to the environment for GPUs that aren’t conformant to any Vulkan version before running any Vulkan content.

The following hardware is currently in active development:

Product | Series | B.V.N.C | Vulkan
--- | --- | --- | ---
AXE-1-16M | A-Series | 33.15.11.3 | 1.2
BXM-4-64 | B-Series | 36.52.104.182 | 1.2
BXM-4-64 | B-Series | 36.56.104.183 | 1.2
BXS-4-64 | B-Series | 36.53.104.796 | 1.2

The following hardware is partially supported and not currently under active development:

Product | Series | B.V.N.C | Vulkan
--- | --- | --- | ---
GX6250 | Series 6XT | 4.40.2.51 | 1.2

Various core-specific features and workarounds are likely to be unimplemented for this hardware. Some very simple Vulkan applications may run unhindered, but instability and corruption are to be expected until additional feature support and workarounds are in place.

The following hardware is unsupported and not under active development:

Product | Series | B.V.N.C
--- | --- | ---
G6110 | Series 6XE | 5.9.1.46
GX6250 | Series 6XT | 4.45.2.58
GX6650 | Series 6XT | 4.46.6.62
GE7800 | Series 7XE | 15.5.1.64
GE8300 | Series 8XE | 22.67.54.30
GE8300 | Series 8XE | 22.68.54.30
GE8300 | Series 8XE | 22.102.54.38
BXE-2-32 | B-Series | 36.29.52.182
BXE-4-32 | B-Series | 36.50.54.182

Device info and firmware have been made available for these devices, typically due to community requests or interest, but no support is guaranteed beyond this.

In some cases, a product name is shared across multiple BVNCs so to check for support make sure the BVNC matches the one listed. As the feature set and hardware issues can vary between BVNCs, additional driver changes might be necessary even for devices sharing the same product name.

Hardware documentation can be found at: https://docs.imgtec.com/

Note: GPUs prior to Series6 do not have the hardware capabilities required to support Vulkan and therefore cannot be supported by this driver.

## Multi-Architecture support

To support multiple distinct hardware generations without too much spaghetti-code, the PowerVR build compiles a few files multiple times (once per hardware architecture) and uses a system of macros and aliases to be able to refer to the different versions.

The files that get compiled multiple times are those named `pvr_arch_*.c`. These files contain definitions of functions prefixed with `pvr_arch_` (instead of the normal `pvr_`-prefix). The `arch`-bit of that function is a placeholder, which gets replaced at compile-time, thanks to a system of defines in the corresponding header file, supported by a set of macros defined in `pvr_macros.h`.

The intention is that these functions are mostly called from architecture specific entrypoints, that are handled by the common vulkan dispatch-table code. This means that an architecture specific function can easily call either architecture specific or architecture agnostic code.

The tricky bit comes when architecture agnostic code calls architecture specific code. In that case, we have the `PVR_ARCH_DISPATCH` and `PVR_ARCH_DISPATCH_RET` macros. These are a bit error-prone to use because they need to see definitions for all architecture versions of each entrypoint, which isn’t something we have available. To work around this, we define a `PER_ARCH_FUNCS(arch)` macro in each source-file that needs to use these dispatch macros and make sure to instantiate it once per architecture.

To avoid confusion, please do not add functions that are prefixed with `pvr_arch_` if they are not part of the system described here.

## drm-shim

PowerVR implements `drm-shim`, stubbing out the powervr DRM kernel interface. This allows for use-cases such as offline compiler testing and control-stream dumping.

To build Mesa with the PowerVR drm-shim, configure Meson with `-Dvulkan-drivers=imagination` and `-Dtools=drm-shim`. The drm-shim binary will be built to `build/src/imagination/drm-shim/libpowervr_noop_drm_shim.so`.

To use, set the `LD_PRELOAD` environment variable to the drm-shim binary.

By default, drm-shim mocks a BXS-4-64 with a BVNC of 36.53.104.796, however this can be overridden by setting the `PVR_SHIM_DEVICE_BVNC` environment variable. The value to set should match those found in the `struct pvr_device_ident` instances defined in `src/imagination/common/device_info/*.h`.

The reported quirks and enhancements can be overridden by setting the `PVR_SHIM_MUSTHAVE_QUIRKS`, `PVR_SHIM_QUIRKS`, and `PVR_SHIM_ENHANCEMENTS` environment variables. These should be set to a comma/semicolon-separated list of quirk/enhancement IDs.

## Chat

PowerVR developers and users hang out on IRC at `#powervr` on OFTC. Note that registering and authenticating with `NickServ` is required to prevent spam. Join the chat.

## Hardware glossary

BVNC

  Set of four numbers used to uniquely identify each GPU (Series6 onwards). This is used to determine the GPU feature set, along with any known hardware issues.