[PATCH v2 0/3] Rust abstractions for the SPI driver subsystem

[PATCH v2 0/3] Rust abstractions for the SPI driver subsystem

[Shuai Liu]

Changes since v1:
  - guard rust/helpers/spi.c with CONFIG_SPI and only build the module
    in lib.rs when CONFIG_SPI is enabled, fixing a link error with
    CONFIG_RUST=y and CONFIG_SPI=n
  - fix the match data lookup order in probe_callback(): OF/ACPI match
    data first, then the SPI id table, matching the C core's
    spi_get_device_match_data()
  - copy data into DMA-safe bounce buffers in write(), read() and
    write_then_read(); the SPI core requires transfer buffers to be
    DMA-safe, while caller-provided slices may be located anywhere
    (e.g. on the stack)

The first three changes were found by the Sashiko automated review; the
remaining findings (null handling in spi_id_info() and length overflow
in write_then_read()) turned out to be false positives, as both cases
are already handled.

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@qq.com>

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              | 558 ++++++++++++++++++++++++++++++++
 samples/rust/Kconfig            |  11 +
 samples/rust/Makefile           |   1 +
 samples/rust/rust_driver_spi.rs |  66 ++++
 9 files changed, 676 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