[PATCH 6/7] rust: usb: remove the disconnect() callback

[Danilo Krummrich <dakr@kernel.org>]

The driver model uses native Rust lifetimes to let driver data retain
device resources and an Interface<Bound> reference for the duration of
the binding. Both remain accessible from the destructor, so a separate
disconnect() callback is no longer needed.

Remove usb::Driver::disconnect() and document that device teardown
belongs in Drop or PinnedDrop.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/usb.rs              | 36 ++++++---------------------------
 samples/rust/rust_driver_usb.rs | 11 +++++-----
 2 files changed, 12 insertions(+), 35 deletions(-)

diff --git a/rust/kernel/usb.rs b/rust/kernel/usb.rs
index 993760ff332b..2126378abc95 100644
--- a/rust/kernel/usb.rs
+++ b/rust/kernel/usb.rs
@@ -98,22 +98,8 @@ extern "C" fn probe_callback(
         })
     }
 
-    extern "C" fn disconnect_callback(intf: *mut bindings::usb_interface) {
-        // SAFETY: The USB core only ever calls the disconnect callback with a valid pointer to a
-        // `struct usb_interface`.
-        //
-        // INVARIANT: `intf` is valid for the duration of `disconnect_callback()`.
-        let intf = unsafe { &*intf.cast::<Interface<device::CoreInternal<'_>>>() };
-
-        let dev: &device::Device<device::CoreInternal<'_>> = intf.as_ref();
-
-        // SAFETY: `disconnect_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::Data<'_>>>`.
-        let data = unsafe { dev.drvdata_borrow::<T::Data<'_>>() };
-
-        T::disconnect(intf, data);
-    }
+    // The USB core calls `disconnect` unconditionally.
+    extern "C" fn disconnect_callback(_intf: *mut bindings::usb_interface) {}
 }
 
 /// Abstraction for the USB device ID structure, i.e. [`struct usb_device_id`].
@@ -278,12 +264,6 @@ macro_rules! usb_device_table {
 ///     ) -> impl PinInit<Self::Data<'bound>, Error> + 'bound {
 ///         Err(ENODEV)
 ///     }
-///
-///     fn disconnect<'bound>(
-///         _interface: &'bound usb::Interface<Core<'_>>,
-///         _data: Pin<&Self::Data<'bound>>,
-///     ) {
-///     }
 /// }
 ///```
 pub trait Driver {
@@ -291,6 +271,10 @@ 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 an
+    /// [`Interface<device::Bound>`] reference for use during teardown.
     type Data<'bound>: Send + 'bound;
 
     /// The table of device ids supported by the driver.
@@ -305,14 +289,6 @@ fn probe<'bound>(
         id: &DeviceId,
         id_info: Option<&'bound Self::IdInfo>,
     ) -> impl PinInit<Self::Data<'bound>, Error> + 'bound;
-
-    /// USB driver disconnect.
-    ///
-    /// Called when the USB interface is about to be unbound from this driver.
-    fn disconnect<'bound>(
-        interface: &'bound Interface<device::Core<'_>>,
-        data: Pin<&Self::Data<'bound>>,
-    );
 }
 
 /// A USB interface.
diff --git a/samples/rust/rust_driver_usb.rs b/samples/rust/rust_driver_usb.rs
index 7ef04e177c80..1349fa1a66d1 100644
--- a/samples/rust/rust_driver_usb.rs
+++ b/samples/rust/rust_driver_usb.rs
@@ -14,7 +14,7 @@
 };
 
 struct SampleDriver {
-    _intf: ARef<usb::Interface>,
+    intf: ARef<usb::Interface>,
 }
 
 kernel::usb_device_table!(
@@ -36,12 +36,13 @@ fn probe<'bound>(
         let dev: &device::Device<Core<'_>> = intf.as_ref();
         dev_info!(dev, "Rust USB driver sample probed\n");
 
-        Ok(Self { _intf: intf.into() })
+        Ok(Self { intf: intf.into() })
     }
+}
 
-    fn disconnect<'bound>(intf: &'bound usb::Interface<Core<'_>>, _data: Pin<&Self>) {
-        let dev: &device::Device<Core<'_>> = intf.as_ref();
-        dev_info!(dev, "Rust USB driver sample disconnected\n");
+impl Drop for SampleDriver {
+    fn drop(&mut self) {
+        dev_info!(self.intf, "Rust USB driver sample disconnected\n");
     }
 }
 
-- 
2.56.0