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

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Message-ID: <10637103-7e15-406a-8e9c-0eee3c5c4922@gmail.com>
Date: Sat, 27 Sep 2025 19:20:52 +0100
From: Igor Korotin <igor.korotin.linux@...il.com>
To: Danilo Krummrich <dakr@...nel.org>
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

Hello Danilo

On 9/11/2025 9:46 PM, Danilo Krummrich wrote:
> 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. :)

I literally just unwrapped module_driver! macro to get to the init 
function.
This type was part of that macro. I do not see it necessary, so I'll 
remove it
in the next drop.
  >> +
>> +                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.

Well, as far as I traced the C code, `adapter->dev` is a 
`client->dev->parent`. Inside of the i2c_new_client_device the new 
created client device is being registered and as part of this 
registration device's parent reference count is being incremented.

A big thanks for the review and comments.

Regards
Igor