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

[Igor Korotin <igor.korotin@linux.dev>]

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