[PATCH v2 0/4] Add Rust abstractions for nvmem-provider

[Link Mauve]

Hi, this is my first foray in Rust in the kernel!  I’m fairly used to
both Rust and the kernel, but not yet to both at the same time.

I wanted to try something simple before jumping to more advanced stuff
like DRM or V4L2 drivers, so I set on rewriting one of my old Wii
drivers in Rust.

I made sure there was no unsafe anywhere in the driver, and tried to
keep it to as few places as possible in the nvmem abstraction.

I’ve tested it on a Wii, using a downstream branch[1], plus the PowerPC
support patch[2], plus a terrible patch to make libcore not use integer
division on u64 or u128[3].  I’ve tested that the data I get out of this
driver result to the same data as the previous C driver.

Thanks for your time!

[1] https://github.com/Wii-Linux/wii-linux-ngx/commits/wii-mainline
[2] https://lore.kernel.org/rust-for-linux/20260204030507.8203-1-linkmauve@linkmauve.fr/T/
[3] https://linkmauve.fr/files/0001-XXX-Unimplement-core-fmt-on-u64-u128-and-Duration.patch

Changes since v1:
- Add Rust helpers to read and write as big endian.
- Set CONFIG_RUST=y in the Wii defconfig.
- Drop the patch to document nvmem-provider.h, this can go in a latter
  series.

In the nvmem abstractions:
- Replace as pointer casts with .cast(), .cast_const() and .cast_mut().
- Replace NvmemConfig::set_*() with NvmemConfig::with_*() to allow the
  builder pattern.
- Expose devm_nvmem_register() on Device instead of in NvmemConfig,
  making it both more correct and more evident coming from C.
- Make it set priv, reg_read and reg_write, as those are managed by the
  abstraction.

In the nintendo-otp driver:
- Add missing RUST depends
- Remove unnecessary reference to pdev in the driver.
- Simplify the loop using while let instead of break.
- Remove unnecessary Drop impl.
- Adapt to the NvmemConfig changes.
- Use c"" instead of c_str!().
- Correctly read and write as big endian.
- Keep a pinned reference to the iomem, otherwise the driver will crash
  trying to access unmapped memory.

Link Mauve (4):
  rust: io: Add big-endian read and write functions
  rust: nvmem: Add an abstraction for nvmem providers
  nvmem: Replace the Wii and Wii U OTP driver with a Rust one
  powerpc: wii_defconfig: Enable Rust

 arch/powerpc/configs/wii_defconfig |   1 +
 drivers/nvmem/Kconfig              |   1 +
 drivers/nvmem/Makefile             |   2 +-
 drivers/nvmem/nintendo-otp.c       | 122 ---------------------
 drivers/nvmem/nintendo_otp.rs      | 127 ++++++++++++++++++++++
 rust/bindings/bindings_helper.h    |   1 +
 rust/helpers/io.c                  |  34 ++++++
 rust/kernel/io.rs                  |  18 ++++
 rust/kernel/lib.rs                 |   2 +
 rust/kernel/nvmem.rs               | 163 +++++++++++++++++++++++++++++
 10 files changed, 348 insertions(+), 123 deletions(-)
 delete mode 100644 drivers/nvmem/nintendo-otp.c
 create mode 100644 drivers/nvmem/nintendo_otp.rs
 create mode 100644 rust/kernel/nvmem.rs

-- 
2.52.0