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Update Tyr Upstream Development Process #55

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90 changes: 26 additions & 64 deletions src/Tyr-GPU-Driver.md
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Expand Up @@ -2,17 +2,13 @@

## What is Tyr?

Tyr is a new Rust-based DRM driver for CSF-based Arm Mali GPUs. It is a port of
Panthor — a driver written in C for the same hardware — and written as a joint
effort between Collabora, Arm and Google engineers.
Tyr is a new Rust-based DRM driver for CSF-based Arm Mali GPUs. It is a Rust
reimplementation of Panthor — a driver written in C for the same hardware —
developed jointly by Collabora, Arm, and Google engineers.

Tyr aims to eventually implement the same userspace API offered by Panthor for
compatibility reasons, so that it can be used as a drop-in replacement in our
Vulkan driver, called
[PanVK](https://gitlab.freedesktop.org/mesa/mesa/-/tree/main/src/panfrost/vulkan?ref_type=heads).
In any case, we foresee Panthor being used — and of course supported — for a
relatively long time, as it is a mature driver with a large adoption in the
ecosystem. It will probably take a couple of years for Tyr to fully pick up.
compatibility reasons, so that it can be used as a drop-in replacement by the
[PanVK](https://gitlab.freedesktop.org/mesa/mesa/-/tree/main/src/panfrost/vulkan?ref_type=heads) Vulkan driver.

## Where is Tyr developed?

Expand All @@ -22,76 +18,42 @@ Tyr is developed both upstream and downstream.

The initial skeleton of the Tyr driver is now [upstream](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/tyr). Submissions against
the upstream Tyr driver should go to the [`dri-devel`](https://lore.kernel.org/dri-devel/)
and [`rust-for-linux`](https://lore.kernel.org/rust-for-linux/) mailing lists. If the
submission is larger and/or needs to be pre-reviewed, open a merge request
against the
[`tyr-for-upstream`](https://gitlab.freedesktop.org/panfrost/linux/-/tree/tyr-for-upstream)
branch in the [`panfrost/linux`](https://gitlab.freedesktop.org/panfrost/linux)
repository.
and [`rust-for-linux`](https://lore.kernel.org/rust-for-linux/) mailing lists.

Tyr commits should usually apply cleanly to [`drm-rust-next`](https://gitlab.freedesktop.org/drm/rust/kernel.git).

### Downstream

A more complete implementation of the Tyr driver is also available in the
Patches that are close to going upstream are collected for convenience in the
[`tyr-for-upstream`](https://gitlab.freedesktop.org/panfrost/linux/-/tree/tyr-for-upstream) branch.

A work-in-progress implementation of the full Tyr driver is also available in the
[`tyr-dev`](https://gitlab.freedesktop.org/panfrost/linux/-/tree/tyr-dev) branch.
Make submissions against the downstream Tyr driver by opening a merge request
against `tyr-dev`. It's expected that `tyr-dev` will be significantly
refactored before upstreaming.

This split is unfortunately necessary as we do not have the required
infrastructure in upstream yet, although our plan is to eventually migrate to
an upstream-only development model once this changes.

We go into more details about why we chose to develop Tyr this way on our
series of [blog
posts](https://www.collabora.com/news-and-blog/news-and-events/introducing-tyr-a-new-rust-drm-driver.html)
at [Collabora's blog](https://www.collabora.com/news-and-blog/). Anyone willing
to get acquainted with Mali's open source stack should refer to that, as we
will be covering the whole infrastructure from a simple Vulkan application to
the actual GPU hardware in Mali's CSF architecture. We will also cover the
various components needed to write a driver, as well as the status of the
abstractions needed to interact with them from Rust code.

As it currently stands, our downstream branch can be used to test the
abstractions that are still being developed. It makes sure that we can write a
functional driver with the abstractions that are currently being proposed.

## What is the current status of the driver?

The current upstream driver can power up the GPU and probe the device on an
RK3588 system-on-chip. This lets us read a few sections of ROM in the GPU,
which in turn lets us provide this information to userspace by means of a
`DRM_IOCTL_PANTHOR_DEV_QUERY` call.
## What is the current status of the driver?

This is all that can be done for now in upstream code, at least until the Micro
Controller Unit can be made to work.
The current upstream driver can probe and register an Arm Mali Valhall CSF GPU,
currently tested on RK3588 systems. During probe it enables the required clocks
and regulators, maps the GPU registers, issues a soft reset, powers on the L2
block, reads the GPU identification and feature registers, and exposes that
information to userspace through `DRM_IOCTL_PANTHOR_DEV_QUERY`.

Our downstream branch (`tyr-dev`) provides a full, working prototype that can run GNOME, Weston, and full-screen 3D games like SuperTuxKart: see [Racing karts on a Rust GPU kernel driver](https://www.collabora.com/news-and-blog/news-and-events/racing-karts-on-a-rust-gpu-kernel-driver.html).
The next major milestone is the Microcontroller Unit (MCU) firmware bring-up.
Until that is in place, the upstream driver is limited to device probing and
basic GPU information queries.

## Can I try it out?

Anyone with a RK3588 SoC can test Tyr, but the driver is not capable of
Anyone with an RK3588 SoC can test Tyr, but the driver is not capable of
replacing Panthor yet. A good candidate device is Radxa's
[ROCK 5B](https://radxa.com/products/rock5/5b/) Single Board Computer.

A good starting point is to use the Tyr driver to run the Panthor [IGT
A good starting point is to experiment with the Panthor [IGT
tests](https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/tree/master/tests/panthor).
While only a subset of the tests pass on the upstream code for the reasons
highlighted above, they should all pass if run on `tyr-dev`.

Note that Mali GPUs are found in a vast array of devices, and that we will
support more hardware as we progress in the implementation.

## Contributing

Tyr is open-source software, and as such, anyone interested in its development
can check our [issue
board](https://gitlab.freedesktop.org/panfrost/linux/-/issues/?label_name%5B%5D=tyr).
We will be posting good starting tasks at a future point.

To work on any given task, assign it to yourself and follow up with a merge
request against `tyr-for-upstream` (for patches targeting the upstream driver)
or `tyr-dev` (for work in the downstream staging branch).

Please also write the IGT tests needed to ensure that your code works.
If you would like to contribute, check our [issue
board](https://gitlab.freedesktop.org/panfrost/linux/-/issues/?label_name%5B%5D=tyr)
to look for open tasks.

Happy hacking!