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, 11 insertions, 7 deletions

diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
index 35b44d194f67..4e83f9e27d78 100644
--- a/rust/kernel/auxiliary.rs
+++ b/rust/kernel/auxiliary.rs
@@ -41,12 +41,12 @@ pub struct Adapter<T: Driver>(T);
 
 // SAFETY:
 // - `bindings::auxiliary_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 auxiliary_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::auxiliary_driver;
-    type DriverData = T;
+    type DriverData<'bound> = T::Data;
     const DEVICE_DRIVER_OFFSET: usize = core::mem::offset_of!(Self::DriverType, driver);
 }
 
@@ -111,8 +111,8 @@ impl<T: Driver> Adapter<T> {
 
         // 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>>`.
-        let data = unsafe { adev.as_ref().drvdata_borrow::<T>() };
+        // and stored a `Pin<KBox<T::Data>>`.
+        let data = unsafe { adev.as_ref().drvdata_borrow::<T::Data>() };
 
         T::unbind(adev, data);
     }
@@ -202,13 +202,17 @@ pub trait Driver {
     /// type IdInfo: 'static = ();
     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>;
 
     /// Auxiliary driver probe.
     ///
     /// Called when an auxiliary device is matches a corresponding driver.
-    fn probe(dev: &Device<device::Core>, id_info: &Self::IdInfo) -> impl PinInit<Self, Error>;
+    fn probe(dev: &Device<device::Core>, id_info: &Self::IdInfo)
+        -> impl PinInit<Self::Data, Error>;
 
     /// Auxiliary driver unbind.
     ///
@@ -219,8 +223,8 @@ pub trait Driver {
     /// `&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 `Self::drop`.
-    fn unbind(dev: &Device<device::Core>, this: Pin<&Self>) {
+    /// Otherwise, release operations for driver resources should be performed in `Drop`.
+    fn unbind(dev: &Device<device::Core>, this: Pin<&Self::Data>) {
         let _ = (dev, this);
     }
 }