Re: [PATCH 0/5] rust: extend I2C functionality

["Danilo Krummrich" <dakr@kernel.org>]

(Cc: Bartosz, Greg, Rafael, driver-core)

On Sat Jan 31, 2026 at 3:12 PM CET, Igor Korotin via B4 Relay wrote:
> This patch series extend the existing I2C functionality with:
> - Abstractions allowing to implement I2C algorithms used by I2C adapters;
> - Abstractions allowing to create and add new I2C adapters;
> - Safe wrappers upon I2C and SMbus transferring C API: read/write
>   bytes/words/byte arrays.
>
> The patch series contains additional new sample driver `rust_i2c_adapter`
> presenting the new functionality. 

The i2c_adapter code on the C side has some lifetime issues, Bartosz looks into
resolving.

My biggest concern is that struct i2c_adapter is a bus device implementation,
but does not use the reference count of the embedded struct device.

Instead, I2C bus drivers embedd the i2c_adapter in their driver specific
structure, which is typically freed in the I2C bus driver's remove() callback.

This violates struct device reference counts.

Until this is fixed, the Rust abstractions should probably work around this, to
subsequent painful rework.

> Patch series depend on 
> message-id: <20260107103511.570525-1-dakr@kernel.org>
>
> Signed-off-by: Igor Korotin <igor.korotin.linux@gmail.com>
> ---
> Igor Korotin (5):
>       rust: i2c: split client and adapter code into separate files
>       rust: bits: add define_flags macro
>       rust: i2c: Add I2C Adapter registration abstractions
>       rust: i2c: add I2C wrappers
>       samples: rust: add Rust I2C adapter registration sample
>
>  MAINTAINERS                      |   4 +-
>  include/linux/i2c.h              |   6 +
>  rust/helpers/helpers.c           |   1 +
>  rust/helpers/i2c.c               |  15 ++
>  rust/kernel/bits.rs              |  57 ++++++++
>  rust/kernel/i2c.rs               | 254 ++-------------------------------
>  rust/kernel/i2c/adapter.rs       | 200 ++++++++++++++++++++++++++
>  rust/kernel/i2c/algo.rs          | 300 +++++++++++++++++++++++++++++++++++++++
>  rust/kernel/i2c/client.rs        | 284 ++++++++++++++++++++++++++++++++++++
>  samples/rust/Kconfig             |  12 ++
>  samples/rust/Makefile            |   1 +
>  samples/rust/rust_driver_i2c.rs  |  10 +-
>  samples/rust/rust_i2c_adapter.rs | 170 ++++++++++++++++++++++
>  samples/rust/rust_i2c_client.rs  |  15 +-
>  14 files changed, 1069 insertions(+), 260 deletions(-)
> ---
> base-commit: a7c013f779530190d0c1e1aa5e7c8a61f0bd479e
> change-id: 20260131-i2c-adapter-d38d330c4c25
> prerequisite-message-id: <20260107103511.570525-1-dakr@kernel.org>
> prerequisite-patch-id: 6e4d28a06d842ddfc7db82f410532a35b8fe317d
> prerequisite-patch-id: 9739295d85b688257fca29be1e1217a05a69c9e7
> prerequisite-patch-id: 78eaed3746a40713f44f13508fcf43653b0a4528
> prerequisite-patch-id: 99f1881bc896896297a903affcfa4f62cab1a307
> prerequisite-patch-id: ea8baa9d648f1178d6f39d140b98bddf3c183f6f
> prerequisite-patch-id: f8a9e049d204bde04e80151a67dfff5ec2633e7a
>
> Best regards,
> -- 
> Igor Korotin <igor.korotin.linux@gmail.com>