linux-kernel - Re: [PATCH v5 3/3] samples: rust: add Rust I2C sample driver

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Message-Id: <DCQ9K980YX1W.HZIQI6S5MST9@kernel.org>
Date: Thu, 11 Sep 2025 22:46:27 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Igor Korotin" <igor.korotin.linux@...il.com>
Cc: "Miguel Ojeda" <ojeda@...nel.org>, "Alex Gaynor"
 <alex.gaynor@...il.com>, "Wolfram Sang" <wsa+renesas@...g-engineering.com>,
 "Boqun Feng" <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Alice
 Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>, "Greg
 Kroah-Hartman" <gregkh@...uxfoundation.org>, "Viresh Kumar"
 <viresh.kumar@...aro.org>, "Asahi Lina" <lina+kernel@...hilina.net>,
 "Wedson Almeida Filho" <wedsonaf@...il.com>, "Alex Hung"
 <alex.hung@....com>, "Tamir Duberstein" <tamird@...il.com>, "Xiangfei Ding"
 <dingxiangfei2009@...il.com>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, <linux-i2c@...r.kernel.org>
Subject: Re: [PATCH v5 3/3] samples: rust: add Rust I2C sample driver

On Thu Sep 11, 2025 at 5:50 PM CEST, Igor Korotin wrote:
> +// NOTE: The code below is expanded macro module_i2c_driver. It is not used here
> +//       because we need to manually create an I2C client in `init()`. The macro
> +//       hides `init()`, so to demo client creation on adapter SAMPLE_I2C_ADAPTER_INDEX
> +//       we expand it by hand.
> +type Ops<T> = kernel::i2c::Adapter<T>;

Not a huge fan of this type alias, but up to you. :)

> +#[pin_data]
> +struct DriverModule {
> +    #[pin]
> +    _driver: kernel::driver::Registration<Ops<SampleDriver>>,
> +    _reg: i2c::Registration,
> +}
> +
> +impl kernel::InPlaceModule for DriverModule {
> +    fn init(
> +        module: &'static kernel::ThisModule,
> +    ) -> impl ::pin_init::PinInit<Self, kernel::error::Error> {
> +        kernel::try_pin_init!(Self {
> +            _reg <- {
> +                let adapter = i2c::I2cAdapter::<Normal>::get(SAMPLE_I2C_ADAPTER_INDEX)?;

Just i2c::I2cAdapter::get() is fine.

> +
> +                i2c::Registration::new(adapter.as_ref(), &BOARD_INFO)

Does i2c_new_client_device() grab a reference count of the adapter? If not, you
have to store an ARef<I2cAdapter> within your i2c::Registration as well.

> +            },
> +            _driver <- kernel::driver::Registration::new(<Self as kernel::ModuleMetadata>::NAME,module,),
> +        })
> +    }
> +}