The underlying `struct device` is the same for all device contexts;
`Bound` is a zero-sized type-state marker that does not affect thread
safety. Implement `Sync` for `Device<Bound>` with the same safety
argument as the existing `Device<Normal>` implementation.

This is needed for types that hold `&'a Device<Bound>`, such as
`io::mem::IoMem`, to be `Send`.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/device.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index 09cbe8a438a9..b330b87178d3 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -503,6 +503,10 @@ unsafe impl Send for Device {}
 // synchronization in `struct device`.
 unsafe impl Sync for Device {}
 
+// SAFETY: Same as `Device<Normal>` -- the underlying `struct device` is the same; `Bound` is a
+// zero-sized type-state marker that does not affect thread safety.
+unsafe impl Sync for Device<Bound> {}
+
 /// Marker trait for the context or scope of a bus specific device.
 ///
 /// [`DeviceContext`] is a marker trait for types representing the context of a bus specific
-- 
2.54.0