[PATCH 1/7] rust: pci: remove the unbind() callback

[Danilo Krummrich <dakr@kernel.org>]

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 pci::Driver::unbind() and the adapter's remove callback and
document that device teardown belongs in Drop or PinnedDrop.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/pci.rs              | 34 ++++-----------------------------
 samples/rust/rust_driver_pci.rs |  7 ++-----
 2 files changed, 6 insertions(+), 35 deletions(-)

diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
index 0e9455fd544d..8101c58da6f4 100644
--- a/rust/kernel/pci.rs
+++ b/rust/kernel/pci.rs
@@ -90,7 +90,6 @@ unsafe fn register(
         unsafe {
             (*pdrv.get()).name = name.as_char_ptr();
             (*pdrv.get()).probe = Some(Self::probe_callback);
-            (*pdrv.get()).remove = Some(Self::remove_callback);
             (*pdrv.get()).id_table = T::ID_TABLE.as_ptr();
         }
 
@@ -133,21 +132,6 @@ extern "C" fn probe_callback(
             Ok(0)
         })
     }
-
-    extern "C" fn remove_callback(pdev: *mut bindings::pci_dev) {
-        // SAFETY: The PCI bus only ever calls the remove callback with a valid pointer to a
-        // `struct pci_dev`.
-        //
-        // INVARIANT: `pdev` is valid for the duration of `remove_callback()`.
-        let pdev = unsafe { &*pdev.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<T::Data<'_>>>`.
-        let data = unsafe { pdev.as_ref().drvdata_borrow::<T::Data<'_>>() };
-
-        T::unbind(pdev, data);
-    }
 }
 
 /// Declares a kernel module that exposes a single PCI driver.
@@ -305,6 +289,10 @@ 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 + 'bound;
 
     /// The table of device ids supported by the driver.
@@ -318,20 +306,6 @@ fn probe<'bound>(
         dev: &'bound Device<device::Core<'_>>,
         id_info: Option<&'bound Self::IdInfo>,
     ) -> impl PinInit<Self::Data<'bound>, Error> + 'bound;
-
-    /// PCI 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, drivers may try to perform I/O
-    /// operations to gracefully tear down the device.
-    ///
-    /// Otherwise, release operations for driver resources should be performed in `Drop`.
-    fn unbind<'bound>(dev: &'bound Device<device::Core<'_>>, this: Pin<&Self::Data<'bound>>) {
-        let _ = (dev, this);
-    }
 }
 
 /// The PCI device representation.
diff --git a/samples/rust/rust_driver_pci.rs b/samples/rust/rust_driver_pci.rs
index 13b035a95756..6bd4c1ff11ee 100644
--- a/samples/rust/rust_driver_pci.rs
+++ b/samples/rust/rust_driver_pci.rs
@@ -176,15 +176,12 @@ fn probe<'bound>(
             index: *info,
         })
     }
-
-    fn unbind<'bound>(_pdev: &'bound pci::Device<Core<'_>>, this: Pin<&Self::Data<'bound>>) {
-        this.bar
-            .write_reg(regs::TEST::zeroed().with_index(this.index));
-    }
 }
 
 impl Drop for SampleDriverData<'_> {
     fn drop(&mut self) {
+        self.bar
+            .write_reg(regs::TEST::zeroed().with_index(self.index));
         dev_dbg!(self.pdev, "Remove Rust PCI driver sample.\n");
     }
 }
-- 
2.56.0