Re: [PATCH 4/7] rust: serdev: remove the unbind() callback

[Markus Probst]

On Thu, 2026-11-12 at 01:52 +0100, Danilo Krummrich wrote:
> The driver model uses native Rust lifetimes to let driver data retain
> device resources and a Device<Bound> reference for the duration of the
> binding. Both remain accessible from the destructor, so a separate
> unbind() callback is no longer needed.
> 
> Remove serdev::Driver::unbind() and the adapter's remove callback and
> document that device teardown belongs in Drop or PinnedDrop.
> 
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> ---
>  rust/kernel/serdev.rs | 41 ++++-------------------------------------
>  1 file changed, 4 insertions(+), 37 deletions(-)
> 
> diff --git a/rust/kernel/serdev.rs b/rust/kernel/serdev.rs
> index 17ca504b7f8d..fd998b68b74f 100644
> --- a/rust/kernel/serdev.rs
> +++ b/rust/kernel/serdev.rs
> @@ -81,7 +81,6 @@ unsafe fn register(
>          unsafe {
>              (*sdrv.get()).driver.name = name.as_char_ptr();
>              (*sdrv.get()).probe = Some(Self::probe_callback);
> -            (*sdrv.get()).remove = Some(Self::remove_callback);
>              (*sdrv.get()).driver.of_match_table = of_table;
>              (*sdrv.get()).driver.acpi_match_table = acpi_table;
>          }
> @@ -210,29 +209,6 @@ extern "C" fn probe_callback(sdev: *mut bindings::serdev_device) -> kernel::ffi:
>          })
>      }
>  
> -    extern "C" fn remove_callback(sdev: *mut bindings::serdev_device) {
> -        // SAFETY: The serial device bus only ever calls the remove callback with a valid pointer
> -        // to a `struct serdev_device`.
> -        //
> -        // INVARIANT: `sdev` is valid for the duration of `remove_callback()`.
> -        let sdev = unsafe { &*sdev.cast::<Device<device::CoreInternal<'_>>>() };
> -
> -        // SAFETY: `remove_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<PrivateData<'_, T>>>`.
> -        let private_data = unsafe { sdev.as_ref().drvdata_borrow::<PrivateData<'_, T>>() };
> -
> -        // SAFETY: No one has exclusive access to `private_data.driver`.
> -        let data = unsafe { &*private_data.driver.get() };
> -        // SAFETY:
> -        // - `private_data.driver` is pinned.
> -        // - `remove_callback` is only ever called after a successful call to `probe_callback`,
> -        //   hence it's guaranteed that `private_data.driver` was initialized.
> -        let data_pinned = unsafe { Pin::new_unchecked(data.assume_init_ref()) };
> -
> -        T::unbind(sdev, data_pinned);
> -    }
> -
>      extern "C" fn receive_buf_callback(
>          sdev: *mut bindings::serdev_device,
>          buf: *const u8,
> @@ -365,6 +341,10 @@ pub trait Driver {
>      type IdInfo: 'static;
>  
>      /// The type of the driver's bus device private data.
> +    ///
> +    /// Device teardown should be performed in [`Drop`] or [`PinnedDrop`](pin_init::PinnedDrop)
> +    /// for this type. The `'bound` lifetime allows the data to retain device resources and a
> +    /// [`Device<device::Bound>`] reference for use during teardown.
>      type Data<'bound>: Send + Sync + 'bound;
>  
>      /// The table of OF device ids supported by the driver.
> @@ -382,19 +362,6 @@ fn probe<'bound>(
>          id_info: Option<&'bound Self::IdInfo>,
>      ) -> impl PinInit<Self::Data<'bound>, Error> + 'bound;
>  
> -    /// Serial device bus device driver unbind.
> -    ///
> -    /// Called when a [`Device`] is unbound from its bound [`Driver`]. Implementing this callback
> -    /// is optional.
> -    ///
> -    /// This callback serves as a place for drivers to perform teardown operations that require a
> -    /// `&Device<Core>` or `&Device<Bound>` reference. For instance.
> -    ///
> -    /// Otherwise, release operations for driver resources should be performed in `Drop`.
> -    fn unbind<'bound>(sdev: &'bound Device<device::Core<'_>>, this: Pin<&Self::Data<'bound>>) {
> -        let _ = (sdev, this);
> -    }
> -
>      /// Serial device bus device data receive callback.
>      ///
>      /// Called when data got received from device.

Reviewed-by: Markus Probst <markus.probst@xxxxxxxxx>

Thanks
- Markus Probst

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