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

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Message-ID: <70302f35-918e-4dc8-b4f4-30b86064251c@linux.dev>
Date: Sun, 8 Feb 2026 12:34:46 +0000
From: Igor Korotin <igor.korotin@...ux.dev>
To: Danilo Krummrich <dakr@...nel.org>,
 Igor Korotin via B4 Relay <devnull+igor.korotin.linux.gmail.com@...nel.org>
Cc: igor.korotin.linux@...il.com,
 Daniel Almeida <daniel.almeida@...labora.com>,
 Miguel Ojeda <ojeda@...nel.org>, 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>,
 Wolfram Sang <wsa+renesas@...g-engineering.com>,
 linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
 linux-i2c@...r.kernel.org, markus.probst@...teo.de, brgl@...nel.org,
 gregkh@...uxfoundation.org, rafael@...nel.org, driver-core@...ts.linux.dev
Subject: Re: [PATCH 0/5] rust: extend I2C functionality

Hello Danilo

On 1/31/2026 2:26 PM, Danilo Krummrich wrote:
> (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.

just to clarify what is currently implemented on the Rust side.

The Rust I2cAdapter is required to be bound to a parent Device<Bound>. 
The implementation keeps a reference to the embedded struct device 
inside struct i2c_adapter for the entire lifetime of the Rust adapter, 
so its lifetime is tied to the device model.

I am not entirely sure which specific lifetime or refcounting scenario 
you are referring to. If you have a concrete case in mind where this 
would still be problematic, could you please point it out?

Cheers
Igor