rust: driver: decouple driver private data from driver type

Add a type Data<'bound> associated type to all bus driver traits,
decoupling the driver's bus device private data type from the driver
struct itself.

In the context of adding a 'bound lifetime, making this an associated
type has the advantage that it allows us to avoid a driver trait global
lifetime and it avoids the need for ForLt for bus device private data;
both of which make the subsequent implementation by buses much simpler.

All existing drivers and doc examples set type Data = Self to preserve
the current behavior.

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/20260525202921.124698-5-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

1 files changed, 12 insertions, 8 deletions

diff --git a/rust/kernel/usb.rs b/rust/kernel/usb.rs
index 3f62da585281..88721970afcb 100644
--- a/rust/kernel/usb.rs
+++ b/rust/kernel/usb.rs
@@ -36,12 +36,12 @@ pub struct Adapter<T: Driver>(T);
 
 // SAFETY:
 // - `bindings::usb_driver` is a C type declared as `repr(C)`.
-// - `T` is the type of the driver's device private data.
+// - `T::Data` is the type of the driver's device private data.
 // - `struct usb_driver` embeds a `struct device_driver`.
 // - `DEVICE_DRIVER_OFFSET` is the correct byte offset to the embedded `struct device_driver`.
 unsafe impl<T: Driver> driver::DriverLayout for Adapter<T> {
     type DriverType = bindings::usb_driver;
-    type DriverData = T;
+    type DriverData<'bound> = T::Data;
     const DEVICE_DRIVER_OFFSET: usize = core::mem::offset_of!(Self::DriverType, driver);
 }
 
@@ -109,8 +109,8 @@ impl<T: Driver> Adapter<T> {
 
         // 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>>`.
-        let data = unsafe { dev.drvdata_borrow::<T>() };
+        // and stored a `Pin<KBox<T::Data>>`.
+        let data = unsafe { dev.drvdata_borrow::<T::Data>() };
 
         T::disconnect(intf, data);
     }
@@ -287,23 +287,27 @@ macro_rules! usb_device_table {
 ///
 /// impl usb::Driver for MyDriver {
 ///     type IdInfo = ();
+///     type Data = Self;
 ///     const ID_TABLE: usb::IdTable<Self::IdInfo> = &USB_TABLE;
 ///
 ///     fn probe(
 ///         _interface: &usb::Interface<Core>,
 ///         _id: &usb::DeviceId,
 ///         _info: &Self::IdInfo,
-///     ) -> impl PinInit<Self, Error> {
+///     ) -> impl PinInit<Self::Data, Error> {
 ///         Err(ENODEV)
 ///     }
 ///
-///     fn disconnect(_interface: &usb::Interface<Core>, _data: Pin<&Self>) {}
+///     fn disconnect(_interface: &usb::Interface<Core>, _data: Pin<&Self::Data>) {}
 /// }
 ///```
 pub trait Driver {
     /// The type holding information about each one of the device ids supported by the driver.
     type IdInfo: 'static;
 
+    /// The type of the driver's bus device private data.
+    type Data: Send;
+
     /// The table of device ids supported by the driver.
     const ID_TABLE: IdTable<Self::IdInfo>;
 
@@ -315,12 +319,12 @@ pub trait Driver {
         interface: &Interface<device::Core>,
         id: &DeviceId,
         id_info: &Self::IdInfo,
-    ) -> impl PinInit<Self, Error>;
+    ) -> impl PinInit<Self::Data, Error>;
 
     /// USB driver disconnect.
     ///
     /// Called when the USB interface is about to be unbound from this driver.
-    fn disconnect(interface: &Interface<device::Core>, data: Pin<&Self>);
+    fn disconnect(interface: &Interface<device::Core>, data: Pin<&Self::Data>);
 }
 
 /// A USB interface.