rust: device: WIP(?): Add get_drvdata for AOP series

Signed-off-by: Sasha Finkelstein <fnkl.kernel@gmail.com>
Signed-off-by: Janne Grunau <j@jannau.net>

Author: WhatAmISupposedToPutHere

rust/helpers/device.c

@@ -2,6 +2,11 @@
 
 #include <linux/device.h>
 
+void *rust_helper_dev_get_drvdata(struct device *dev)
+{
+	return dev_get_drvdata(dev);
+}
+
 int rust_helper_devm_add_action(struct device *dev,
 				void (*action)(void *),
 				void *data)

rust/kernel/device.rs

@@ -90,6 +90,13 @@ impl<Ctx: DeviceContext> Device<Ctx> {
         }
     }
 
+    /// Returns the driver_data pointer.
+    pub fn get_drvdata<T>(&self) -> *mut T {
+        // SAFETY: dev_get_drvdata returns a field of the device,
+        //   pointer to which is valid by type invariant
+        unsafe { bindings::dev_get_drvdata(self.as_raw()) as *mut T }
+    }
+
     /// Convert a raw C `struct device` pointer to a `&'a Device`.
     ///
     /// # Safety