[PATCH v3 0/3] Rust abstractions for the SPI driver subsystem

[Shuai Liu]

Changes since v2:
  - use `info_unchecked_opt()` when reading driver data from the SPI id
    table, so that entries without driver data (e.g. `@none` tables) are
    handled gracefully instead of dereferencing a NULL driver_data
  - remove `SpiDevice::setup()`: it modifies device fields without
    holding the I/O mutex and can race with concurrent transfers, and
    it is of little use without corresponding setters
  - drop the bounce buffers in `write_then_read()`: the C core's
    spi_write_then_read() already copies both buffers into internal
    DMA-safe bounce buffers; `write()` and `read()` still bounce, since
    the core functions they call transfer the caller-provided buffer
    directly
  - add `Sync` for `SpiDevice<Bound>` so that device references
    obtained in `probe()` can be stored in driver data; I/O remains
    available from any device context, following the precedent of the
    other bus abstractions (e.g. `usb::Device`)

All of the above were found by the Sashiko automated review.

The Rust abstractions for several buses are already present in the
kernel (PCI, platform, I2C, USB, serdev, ...), but the SPI driver
subsystem is still missing such abstractions. This series adds them,
along with a sample driver demonstrating their usage.

To my knowledge, nobody is currently working on Rust SPI abstractions;
if someone already has work in progress, please let me know and I will
happily drop or rebase this series.

The abstractions follow the same layout as the existing I2C and serdev
abstractions: a `Driver` trait for drivers to implement, an `Adapter`
for driver registration, and a `SpiDevice` wrapping `struct spi_device`.
This first installment provides synchronous `read`, `write` and
`write_then_read` operations; message-based transfers (`spi_message` /
`spi_transfer`) can be added on top in a follow-up series.

One deviation from the I2C abstractions: `spi_match_id()` is not
exported to modules, so device id matching by modalias uses the
exported `spi_get_device_id()` instead, falling back to the OF and ACPI
tables.

The series is based on the current mainline tree (7.4 merge window) and
has been build-tested with CONFIG_RUST=y, including the KUnit tests and
doctests for the new abstractions. I do not have access to real SPI
hardware to run-test this series, but the included sample driver can be
used for that purpose.

Signed-off-by: Shuai Liu <847807867@xxxxxx>

Shuai Liu (3):
  rust: helpers: add SPI helpers
  rust: spi: add SPI driver abstractions
  samples: rust: add SPI driver sample

 rust/bindings/bindings_helper.h |   1 +
 rust/helpers/helpers.c          |   1 +
 rust/helpers/spi.c              |  25 ++
 rust/kernel/Kconfig.test        |  11 +
 rust/kernel/lib.rs              |   2 +
 rust/kernel/spi.rs              | 548 ++++++++++++++++++++++++++++++++
 samples/rust/Kconfig            |  11 +
 samples/rust/Makefile           |   1 +
 samples/rust/rust_driver_spi.rs |  66 ++++
 9 files changed, 666 insertions(+)
 create mode 100644 rust/helpers/spi.c
 create mode 100644 rust/kernel/spi.rs
 create mode 100644 samples/rust/rust_driver_spi.rs

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2.43.0