rust: device: Add a minimal RawDevice trait

Add a RawDevice trait which can be implemented by any type representing
a device class (such as a PlatformDevice). This is the minimum amount of
Device support code required to unblock abstractions that need to take
device pointers.

Lina: Rewrote commit message, and dropped everything except RawDevice.

Co-developed-by: Miguel Ojeda <[email protected]>
Signed-off-by: Miguel Ojeda <[email protected]>
Signed-off-by: Wedson Almeida Filho <[email protected]>
Signed-off-by: Asahi Lina <[email protected]>

Author: wedsonaf

rust/bindings/bindings_helper.h

@@ -7,6 +7,7 @@
  */
 
 #include <kunit/test.h>
+#include <linux/device.h>
 #include <linux/errname.h>
 #include <linux/slab.h>
 #include <linux/refcount.h>

rust/kernel/device.rs

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Generic devices that are part of the kernel's driver model.
+//!
+//! C header: [`include/linux/device.h`](../../../../include/linux/device.h)
+
+use crate::bindings;
+
+/// A raw device.
+///
+/// # Safety
+///
+/// Implementers must ensure that the `*mut device` returned by [`RawDevice::raw_device`] is
+/// related to `self`, that is, actions on it will affect `self`. For example, if one calls
+/// `get_device`, then the refcount on the device represented by `self` will be incremented.
+///
+/// Additionally, implementers must ensure that the device is never renamed. Commit a5462516aa99
+/// ("driver-core: document restrictions on device_rename()") has details on why `device_rename`
+/// should not be used.
+pub unsafe trait RawDevice {
+    /// Returns the raw `struct device` related to `self`.
+    fn raw_device(&self) -> *mut bindings::device;
+}

rust/kernel/lib.rs

@@ -33,6 +33,7 @@ extern crate self as kernel;
 #[cfg(not(testlib))]
 mod allocator;
 mod build_assert;
+pub mod device;
 pub mod error;
 pub mod init;
 pub mod ioctl;