Rust abstractions for network PHY drivers

This patchset adds Rust abstractions for network PHY drivers. It
doesn't fully cover the C APIs for PHY drivers but I think that it's
already useful. I implement two PHY drivers (Asix AX88772A PHYs and
Realtek Generic FE-GE). Seems they work well with real hardware.

Thanks for lots of feedback on v1! I've tried to address them but
sorry if I missed some.

Here are major changes from v1:

- uses rustified enum for C's phy_state enum

This guarantees that C and Rust never diverge. If the C code is
changed without updating the Rust code, compiling the Rust code fails.

Note that C allows using a value that isn't defined in phy_state enum
for phy_state. It leads to undefined behaviour in Rust side. But this
enum is used as state machine in the C side. Such should not
happen. If it happens, it's a bug on the C side.

- adds the Asix driver to drivers/net/phy/ instead of samples/rust/

I've implemented all the features of drivers/net/phy/ax88796b.c. The
features of C and Rust versions are equivalent. You can choose either
on kernel configuration. I suppose that how to handle drivers in Rust
will be discussed in KS or somewhere. Until then, you can use this
to make reviewing the abstractions easier.

- uses static allocation for phy_driver

v1 dynamically allocates memory for phy_driver. v2 uses static
allocation; the registration of drivers is much simpler. I added a
macro that handles registering drivers, building the device id table,
etc.

- cleaning up the interface for PHYLIB

Uses u16 for register and value, keeps genphy_ function names,
dropping lockless_ functions without MDIO bus locked, etc. u8 could be
used for C22 registers but I like to use the same type for C22 and C45.


v1:
https://lwn.net/ml/rust-for-linux/20230913133609.1668758-...

FUJITA Tomonori (3):
  rust: core abstractions for network PHY drivers
  MAINTAINERS: add Rust PHY abstractions file to the ETHERNET PHY
    LIBRARY
  net: phy: add Rust Asix PHY driver

 MAINTAINERS                      |   2 +
 drivers/net/phy/Kconfig          |  16 +
 drivers/net/phy/Makefile         |   8 +-
 drivers/net/phy/ax88796b_rust.rs | 147 ++++++
 rust/Makefile                    |   1 +
 rust/bindings/bindings_helper.h  |   3 +
 rust/kernel/lib.rs               |   3 +
 rust/kernel/net.rs               |   6 +
 rust/kernel/net/phy.rs           | 760 +++++++++++++++++++++++++++++++
 rust/uapi/uapi_helper.h          |   1 +
 10 files changed, 946 insertions(+), 1 deletion(-)
 create mode 100644 drivers/net/phy/ax88796b_rust.rs
 create mode 100644 rust/kernel/net.rs
 create mode 100644 rust/kernel/net/phy.rs


base-commit: 0bb80ecc33a8fb5a682236443c1e740d5c917d1d
-- 
2.34.1