Re: [PATCH v2 3/4] rust: add basic serial device bus abstractions

[Danilo Krummrich]

On Fri Mar 6, 2026 at 8:35 PM CET, Markus Probst wrote:
> +    extern "C" fn receive_buf_callback(
> +        sdev: *mut bindings::serdev_device,
> +        buf: *const u8,
> +        length: usize,
> +    ) -> usize {
> +        // SAFETY: The serial device bus only ever calls the receive buf callback with a valid
> +        // pointer to a `struct serdev_device`.
> +        //
> +        // INVARIANT: `sdev` is valid for the duration of `receive_buf_callback()`.
> +        let sdev = unsafe { &*sdev.cast::<Device<device::CoreInternal>>() };
> +
> +        // SAFETY: `receive_buf_callback` is only ever called after a successful call to
> +        // `probe_callback`, hence it's guaranteed that `Device::set_drvdata()` has been called
> +        // and stored a `Pin<KBox<T>>`.
> +        let data = unsafe { sdev.as_ref().drvdata_borrow::<T>() };
> +
> +        // SAFETY:
> +        // - The serial device bus only ever calls the receive buf callback with a valid pointer to
> +        //   a `struct serdev_device`.
> +        // - `receive_buf_callback` is only ever called after a successful call to
> +        //   `probe_callback`, hence it's guaranteed that `sdev.private_data` is a pointer
> +        //   to a valid `PrivateData`.
> +        let private_data = unsafe { &*(*sdev.as_raw()).private_data.cast::<PrivateData>() };
> +
> +        private_data.probe_complete.complete_all();

Will do a full review pass later on, but one quick question in advance:

What is this used for? It is completed here and in probe(), but I don't see it ever
being used to actually wait.

> +
> +        // SAFETY: No one has exclusive access to `private_data.error`.
> +        if unsafe { *private_data.error.get() } {
> +            return length;
> +        }
> +
> +        // SAFETY: `buf` is guaranteed to be non-null and has the size of `length`.
> +        let buf = unsafe { core::slice::from_raw_parts(buf, length) };
> +
> +        T::receive(sdev, data, buf)
> +    }
> +}