linux-kernel - Re: [PATCH v6 2/3] rust: i2c: add manual I2C device creation abstractions

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Message-ID: <508bd9a1-c75a-4d1d-bed7-ee759ac5a701@kernel.org>
Date: Sun, 26 Oct 2025 11:48:10 +0100
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 v6 2/3] rust: i2c: add manual I2C device creation
 abstractions

On 10/5/25 12:23 PM, Igor Korotin wrote:
> +impl Registration {
> +    /// The C `i2c_new_client_device` function wrapper for manual I2C client creation.
> +    pub fn new(i2c_adapter: &I2cAdapter, i2c_board_info: &I2cBoardInfo) -> Result<Self> {
> +        // SAFETY: the kernel guarantees that `i2c_new_client_device()` returns either a valid
> +        // pointer or NULL. `from_err_ptr` separates errors. Following `NonNull::new` checks for NULL.
> +        let raw_dev = from_err_ptr(unsafe {
> +            bindings::i2c_new_client_device(i2c_adapter.as_raw(), i2c_board_info.as_raw())
> +        })?;
> +
> +        let dev_ptr = NonNull::new(raw_dev).ok_or(ENODEV)?;
> +
> +        Ok(Self(dev_ptr))
> +    }
> +}

I wonder if we want to ensure that a Registration can't out-live the driver that
registers the I2C client device.

This should only ever be called by drivers bound to more complex devices, so if
the parent driver is unbound I don't think I2C client device registered by this
driver should be able to survive.

Hence, I think Registration::new() should return
impl PinInit<Devres<Self>, Error> instead.