rust: add dma coherent allocator abstraction

This series adds the rust bindings for the dma coherent allocator which
is needed for nova-core[0].

For v15, document safety comments on the exception of usage on
read_volatile and write_volatile as suggested by Boqun Feng.

This is tested on a Nvidia GA104 GPU device using PoC code which parses
and loads the GSP firmware via DMA.

Changes since v14:
- Add safety comments on the exception of usage on read_volatile
  and write_volatile (Boqun Feng, Benno Lossin, Andreas Hindborg).
- Link to v14: https://lore.kernel.org/lkml/20250311174930.2348813-1-abd...

Changes since v13:
- Remove Devres wrapper, document correct solution for proper resource
  deallocation as TODO, add patches from Danilo to properly add DMA
  addressing capabilities for the device which requires a new trait
  that defines the DMA specific methods of devices. (Danilo)

Changes since v12:
- Move out the contentious functions: as_slice, as_slice_mut, and write
  for later discussion as a separate patch. Make write unsafe as well.
  Remove skip_drop, use volatile r/w for field_read and field_write
  (Alice Ryhl, et al.).
- Documentation improvements, use markdown for intra-doc links
  (Miguel Ojeda).
- Move dma addressing capabilities to a separate patch within device.rs
  (Andreas Hindborg).
- Add a simple driver to excercise the basics of the api (Danilo).

Changes since v11:
- Ensure robust handling for potential pointer arithmetic overflows
  in bounds checking (Petr Tesařík).
- Add dma mask helpers (Daniel Almeida).
- Clarification in the safety aspects of the as_slice/as_slice_mut API,
  Use ManuallyDrop trait as a replacement for into_parts(),
  Add dma_read!/dma_write! helper macros (Alice Ryhl).

Changes since v10:
- rename read() to as_slice() (Boqun Feng)
- Do a bitwise copy of ARef<Device> in into_parts() when returning the
  device reference (Alice Ryhl).

Changes since v9:
- Use ARef<Device> in the constructor arguments, docs clarification avoid
  manually dropping the refcount for the device in into_parts(), use
  add() instead of wrapping_add() in the pointer arithmetic for performance
  (Alice Ryhl).

Changes since v8:
- Add MAINTAINERS entry
- Fix build issues due to switch from core::ffi to crate:ffi in bindgen.
- Ensure the wrapped attribute is non-pub in struct Attrs, declare it 
  #[repr(transparent)] as well (Daniel Sedlak)

Changes since v7:
- Remove cpu_buf() and cpu_buf_mut() as exporting a r/w interface via
  a slice is undefined behaviour due to slice's requirement that the
  underlying pointer should not be modified (Alice Ryhl, Robin Murphy).
- Reintroduce r/w helpers instead which includes proper safety
  invariants (Daniel Almeida).

Changes since v6:
- Include the dma_attrs in the constructor, use alloc::Flags as inpiration

Changes since v5:
- Remove unnecessary lifetime annotation when returning the CPU buffer.

Changes since v4:
- Documentation and example fixes, use Markdown formatting (Miguel Ojeda).
- Discard read()/write() helpers to remove bound on Copy and fix overhead
  (Daniel Almeida).
- Improve error-handling in the constructor block (Andreas Hindborg).

Changes since v3:
- Reject ZST types by checking the type size in the constructor in
  addition to requiring FromBytes/AsBytes traits for the type (Alice Ryhl).

Changes since v2:
- Fixed missing header for generating the bindings.

Changes since v1:
- Fix missing info in commit log where EOVERFLOW is used.
- Restrict the dma coherent allocator to numeric types for now for valid
  behaviour (Daniel Almeida).
- Build slice dynamically.

[0] https://lore.kernel.org/lkml/20250131220432.17717-1-dakr@...

Abdiel Janulgue (5):
  rust: error: Add EOVERFLOW
  rust: add dma coherent allocator abstraction.
  samples: rust: add Rust dma test sample driver
  MAINTAINERS: add entry for Rust dma mapping helpers device driver API
  rust: dma: add as_slice/write functions for CoherentAllocation

Danilo Krummrich (6):
  rust: dma: implement `dma::Device` trait
  rust: dma: add dma addressing capabilities
  rust: pci: implement the `dma::Device` trait
  rust: platform: implement the `dma::Device` trait
  rust: dma: use `dma::Device` in `CoherentAllocation`
  rust: samples: dma: set DMA mask

 MAINTAINERS                     |  13 +
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers/dma.c              |   8 +
 rust/helpers/helpers.c          |   1 +
 rust/kernel/dma.rs              | 521 ++++++++++++++++++++++++++++++++
 rust/kernel/error.rs            |   1 +
 rust/kernel/lib.rs              |   1 +
 rust/kernel/pci.rs              |   2 +
 rust/kernel/platform.rs         |   2 +
 samples/rust/Kconfig            |  11 +
 samples/rust/Makefile           |   1 +
 samples/rust/rust_dma.rs        | 104 +++++++
 12 files changed, 666 insertions(+)
 create mode 100644 rust/helpers/dma.c
 create mode 100644 rust/kernel/dma.rs
 create mode 100644 samples/rust/rust_dma.rs


base-commit: cf25bc61f8aecad9b0c45fe32697e35ea4b13378
-- 
2.43.0