CONFIG_AUXILIARY_BUS cannot be enabled explicitly, and unless we select
it we have no way to include it (and thus to enable NOVA_CORE) unless
another driver happens to do it for us.

Fixes: e041d81a0377 ("gpu: nova-core: register auxiliary device for nova-drm")
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://lore.kernel.org/r/20250515-aux_bus-v2-2-47c70f96ae9b@nvidia.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Register an auxiliary device for nova-drm.

For now always use zero for the auxiliary device's ID; we don't use it
yet anyways. However, once it lands, we should switch to XArray.

Acked-by: Dave Airlie <airlied@redhat.com>
Link: https://lore.kernel.org/r/20250424160452.8070-2-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Add the initial nova-core driver stub.

nova-core is intended to serve as a common base for nova-drm (the
corresponding DRM driver) and the vGPU manager VFIO driver, serving as a
hard- and firmware abstraction layer for GSP-based NVIDIA GPUs.

The Nova project, including nova-core and nova-drm, in the long term,
is intended to serve as the successor of Nouveau for all GSP-based GPUs.

The motivation for both, starting a successor project for Nouveau and
doing so using the Rust programming language, is documented in detail
through a previous post on the mailing list [1], an LWN article [2] and a
talk from LPC '24.

In order to avoid the chicken and egg problem to require a user to
upstream Rust abstractions, but at the same time require the Rust
abstractions to implement the driver, nova-core kicks off as a driver
stub and is subsequently developed upstream.

Link: https://lore.kernel.org/dri-devel/Zfsj0_tb-0-tNrJy@cassiopeiae/T/#u [1]
Link: https://lwn.net/Articles/990736/ [2]
Link: https://youtu.be/3Igmx28B3BQ?si=sBdSEer4tAPKGpOs [3]
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://lore.kernel.org/r/20250306222336.23482-5-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>