linux-kernel - Re: [PATCH RFC 2/4] rust: add basic serial device bus abstractions

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Message-ID: <4c26408c-b8ce-42a6-b0df-47053fd81eda@gmail.com>
Date: Sun, 21 Dec 2025 10:19:11 +0100
From: Dirk Behme <dirk.behme@...il.com>
To: Markus Probst <markus.probst@...teo.de>, Rob Herring <robh@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jiri Slaby <jirislaby@...nel.org>, 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>,
 Danilo Krummrich <dakr@...nel.org>,
 Kari Argillander <kari.argillander@...il.com>
Cc: linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH RFC 2/4] rust: add basic serial device bus abstractions

Hi Markus,

On 20.12.25 19:44, Markus Probst wrote:
> Implement the basic serial device bus abstractions required to write a
> serial device bus device driver with or without the need for initial device
> data. This includes the following data structures:
> 
> The `serdev::Driver` trait represents the interface to the driver.
> 
> The `serdev::Device` abstraction represents a `struct serdev_device`.
> 
> In order to provide the Serdev specific parts to a generic
> `driver::Registration` the `driver::RegistrationOps` trait is
> implemented by `serdev::Adapter`.
> 
> Co-developed-by: Kari Argillander <kari.argillander@...il.com>
> Signed-off-by: Kari Argillander <kari.argillander@...il.com>
> Signed-off-by: Markus Probst <markus.probst@...teo.de>
> ---
>  rust/bindings/bindings_helper.h |   1 +
>  rust/helpers/helpers.c          |   1 +
>  rust/helpers/serdev.c           |  22 ++
>  rust/kernel/lib.rs              |   2 +
>  rust/kernel/serdev.rs           | 815 ++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 841 insertions(+)
> 
...
> diff --git a/rust/kernel/serdev.rs b/rust/kernel/serdev.rs
> new file mode 100644
> index 000000000000..0f5ef325a054
> --- /dev/null
> +++ b/rust/kernel/serdev.rs
....
> +    /// Write data to the serial device until the controller has accepted all the data or has
> +    /// been interrupted by a timeout or signal.
> +    ///
> +    /// Note that any accepted data has only been buffered by the controller. Use
> +    /// [ Device::wait_until_sent`] to make sure the controller write buffer has actually been
> +    /// emptied.
> +    ///
> +    /// Returns the number of bytes written (less than data if interrupted).

Should it be "less than data.len"? Instead of just "data"? Same in the
comment for `write()`below.


> +    /// [`kernel::error::code::ETIMEDOUT`] or [`kernel::error::code::ERESTARTSYS`] if interrupted
> +    /// before any bytes were written.
> +    pub fn write_all(&self, data: &[u8], timeout: Timeout) -> Result<usize> {
> +        // SAFETY:
> +        // - `self.as_raw()` is guaranteed to be a pointer to a valid `serdev_device`.
> +        // - `data.as_ptr()` is guaranteed to be a valid array pointer with the size of
> +        //   `data.len()`.
> +        let ret = unsafe {
> +            bindings::serdev_device_write(
> +                self.as_raw(),
> +                data.as_ptr(),
> +                data.len(),
> +                timeout.into_jiffies(),
> +            )
> +        };
> +        if ret < 0 {
> +            // CAST: negative return values are guaranteed to be between `-MAX_ERRNO` and `-1`,
> +            // which always fit into a `i32`.
> +            Err(Error::from_errno(ret as i32))
> +        } else {
> +            Ok(ret.unsigned_abs())
> +        }
> +    }
> +
> +    /// Write data to the serial device.
> +    ///
> +    /// If you want to write until the controller has accepted all the data, use
> +    /// [`Device::write_all`].
> +    ///
> +    /// Note that any accepted data has only been buffered by the controller. Use
> +    /// [ Device::wait_until_sent`] to make sure the controller write buffer has actually been
> +    /// emptied.
> +    ///
> +    /// Returns the number of bytes written (less than data if interrupted).
> +    /// [`kernel::error::code::ETIMEDOUT`] or [`kernel::error::code::ERESTARTSYS`] if interrupted
> +    /// before any bytes were written.
> +    pub fn write(&self, data: &[u8]) -> Result<u32> {
> +        // SAFETY:
> +        // - `self.as_raw()` is guaranteed to be a pointer to a valid `serdev_device`.
> +        // - `data.as_ptr()` is guaranteed to be a valid array pointer with the size of
> +        //   `data.len()`.
> +        let ret =
> +            unsafe { bindings::serdev_device_write_buf(self.as_raw(), data.as_ptr(), data.len()) };
> +        if ret < 0 {
> +            Err(Error::from_errno(ret))
> +        } else {
> +            Ok(ret.unsigned_abs())
> +        }
> +    }

Best regards

Dirk