[PATCH v7 00/10] rust: add `register!` macro

[Alexandre Courbot]

New revision addressing the v6 feedback - the use of "location" instead
of "reference" in particular reads well both in the code and the
comments.

As a reminder, since the previous revision we use the I/O type to
perform the actual I/O instead of the register type, which moves us from
this access pattern:

    let boot0 = regs::NV_PMC_BOOT_0::read(bar);

to this arguably more natural one:

    let boot0 = bar.read(regs::NV_PMC_BOOT_0);

This revision is based on `driver-core-testing` as of 2026-02-24 with
[1] applied. A tree with this series and its dependencies is available
at [2].

[1] https://lore.kernel.org/all/20260206-io-v2-0-71dea20a06e6@xxxxxxxxxx/
[2] https://github.com/Gnurou/linux/tree/b4/register

The first patch enables the `generic_arg_infer` feature, which is
required for generic type inference and used in subsequent patches. This
feature is stable since rustc 1.89.

The second patch adds `shr` and `shl` methods to `Bounded`. These were
suggested by Alice during LPC as a way to avoid the use of the
controversial `Bounded::from_expr` in both the bitfield macro and the
Nova code. The third patch adds another convenience method to obtain a
`bool` from single-bit `Bounded`s, while the fourth patch turns
`Bounded::get` into a const method in order to make register setter
methods const.

Patches 5 and 6 introduce the `IoLoc` and `IoWrite` types around which
I/O accesses are centered. This allows registers to be accessed using
the same `read` and `write` methods as primitive types.

Patch 7 adds the `register!` macro and the types it requires.

Patch 8 updates the Rust PCI sample driver to use `register!`, as per
its TODO item.

Patch 9 illustrates more extensively how this macro is used by
converting nova-core to use it, and removing the local implementation.
This patch is to be merged one cycle after the other patches.

Patch 10 is an RFC allowing a shorter write syntax to be used in the
case of fixed or relative registers. It doesn't need to be merged
immediately, but I think it is a good time to discuss it.

I have also removed Gary's signoff on patches 5 and 7 to make sure it
doesn't get merged before he gives it explicitly.

Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>

---
Changes in v7:
- Use `RES + SHIFT >= N` instead of `RES >= N - SHIFT` in
  `Bounded::shr`.
- Rename `IoRef` to `IoLoc` and all related types
  accordingly.
- Use `Into` trait bounds in both directions on `IoLoc`.
- Add RFC patch allowing fixed register values to be used directly with
  `write`.
- Link to v6: https://patch.msgid.link/20260216-register-v6-0-eec9a4de9e9e@xxxxxxxxxx

Changes in v6:
- Remove Tested-by tags as the code has considerably changed.
- Make `Bounded::get` const so it can be used with registers.
- Use the `pin_init::zeroed()` const function instead of defining our
  own method.
- Generalize all `Io` around the new `IoRef` and `IoWrite` types, and
  make registers use these as well.
- Use the more natural pattern of having the `Io` type perform the I/O
  access instead of the register type.
- Convert the whole PCI driver example, and not only the PCI
  configuration space.
- Rename `Bounded::as_bool` to `Bounded::into_bool`.
- Drop `Bounded::into_inner` in favor of making `Bounded::get` const.
- Link to v5: https://patch.msgid.link/20260129-register-v5-0-c4587c902514@xxxxxxxxxx

Changes in v5:
- Rename all setters to `with_*` and `with_const_*`.
- Use `, stride = ` to specify the stride of register arrays.
- Remove `Deref` requirement on the `RegisterIo` trait and make it
  `#[doc(hidden)`.
- Simplify the top dispatch rule a bit.
- Link to v4: https://patch.msgid.link/20260128-register-v4-0-aee3a33d9649@xxxxxxxxxx

Changes in v4:
- Add `with_` const field setter methods (removing the need to call
  `Bounded::new` for constant field values).
- Add `into_inner` const method for `Bounded`.
- Add `from_raw` and const `zeroed` method to create initial register
  values.
- More documentation improvements.
- Link to v3: https://patch.msgid.link/20260126-register-v3-0-2328a59d7312@xxxxxxxxxx

Changes in v3:
- Sort the Rust features list alphabetically.
- Rebase on top of latest `driver-core-next` including the new Io trait.
- Allow several registers to be defined from the same macro invocation.
- Remove references to `bitfield!` macro.
- Fix doccomment of `shr` and `shl`.
- Use `+` syntax for relative register offsets.
- Move register arrays size and stride to after the backing type declaration.
- Use regular doccomments to document registers and fields (thanks Gary!).
- Remove `Default` implementation and implement the more predictable
  `Zeroable` instead.
- Improve doccomments a bit.
- Link to v2: https://patch.msgid.link/20260121-register-v2-0-79d9b8d5e36a@xxxxxxxxxx

Changes in v2:
- Remove `bitfield!` and put its rules into `register!` to give it more
  time to get reviewed.
- Allow output type larger than strictly required for `shr` and `shl` on
  `Bounded`.
- Enable the `generic_arg_infer` feature, required for rustc < 1.89.
- Link to v1: https://patch.msgid.link/20260120-register-v1-0-723a1743b557@xxxxxxxxxx

---
Alexandre Courbot (10):
      rust: enable the `generic_arg_infer` feature
      rust: num: add `shr` and `shl` methods to `Bounded`
      rust: num: add `into_bool` method to `Bounded`
      rust: num: make Bounded::get const
      rust: io: add IoLoc and IoWrite types
      rust: io: use generic read/write accessors for primitive accesses
      rust: io: add `register!` macro
      sample: rust: pci: use `register!` macro
      [FOR REFERENCE] gpu: nova-core: use the kernel `register!` macro
      RFC: rust: io: allow fixed register values directly in `write`

 drivers/gpu/nova-core/falcon.rs           |  249 +++----
 drivers/gpu/nova-core/falcon/gsp.rs       |   23 +-
 drivers/gpu/nova-core/falcon/hal/ga102.rs |   65 +-
 drivers/gpu/nova-core/falcon/hal/tu102.rs |   11 +-
 drivers/gpu/nova-core/falcon/sec2.rs      |   17 +-
 drivers/gpu/nova-core/fb.rs               |    6 +-
 drivers/gpu/nova-core/fb/hal/ga100.rs     |   40 +-
 drivers/gpu/nova-core/fb/hal/ga102.rs     |    7 +-
 drivers/gpu/nova-core/fb/hal/tu102.rs     |   22 +-
 drivers/gpu/nova-core/gfw.rs              |   11 +-
 drivers/gpu/nova-core/gpu.rs              |   36 +-
 drivers/gpu/nova-core/gsp/boot.rs         |   11 +-
 drivers/gpu/nova-core/gsp/cmdq.rs         |   10 +-
 drivers/gpu/nova-core/regs.rs             |  544 ++++++++------
 drivers/gpu/nova-core/regs/macros.rs      |  739 -------------------
 rust/kernel/io.rs                         |  347 +++++++--
 rust/kernel/io/register.rs                | 1135 +++++++++++++++++++++++++++++
 rust/kernel/lib.rs                        |    3 +
 rust/kernel/num/bounded.rs                |   70 +-
 samples/rust/rust_driver_pci.rs           |   84 ++-
 scripts/Makefile.build                    |    3 +-
 21 files changed, 2118 insertions(+), 1315 deletions(-)
---
base-commit: 545225ee0b0b6998c7b6ff888f8497681b8b35c4
change-id: 20260117-register-ccaba1d21713

Best regards,
-- 
Alexandre Courbot <acourbot@xxxxxxxxxx>