[PATCH v4 6/7] rust: completion: add complete()

[Maurice Hieronymus]

The initial completion abstraction only added `complete_all()` and
`wait_for_completion()`. `complete_all()` marks the completion permanently
done, which makes a single `Completion` unsuitable for signalling the same
event repeatedly: once `complete_all()` has run, every subsequent
`wait_for_completion()` returns immediately without waiting.

Add `complete()`, which wakes a single waiter and increments the internal
counter by one. Paired one-to-one with `wait_for_completion()`, it allows
the same completion to be reused across multiple cycles, e.g. to wait for
consecutive DMA transfers to finish.

Acked-by: Gary Guo <gary@xxxxxxxxxxx>
Signed-off-by: Maurice Hieronymus <mhi@xxxxxxxxxxx>
---
 rust/kernel/sync/completion.rs | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync/completion.rs b/rust/kernel/sync/completion.rs
index 1771bfc0ade2..d8150b7b0acb 100644
--- a/rust/kernel/sync/completion.rs
+++ b/rust/kernel/sync/completion.rs
@@ -90,6 +90,17 @@ fn as_raw(&self) -> *mut bindings::completion {
         self.inner.get()
     }
 
+    /// Signal a single task waiting on this completion.
+    ///
+    /// This method wakes up a single task waiting on this completion.
+    /// If no task is currently waiting, the next
+    /// [`Completion::wait_for_completion`] returns immediately.
+    #[inline]
+    pub fn complete(&self) {
+        // SAFETY: `self.as_raw()` is a pointer to a valid `struct completion`.
+        unsafe { bindings::complete(self.as_raw()) };
+    }
+
     /// Signal all tasks waiting on this completion.
     ///
     /// This method wakes up all tasks waiting on this completion; after this operation the
@@ -105,7 +116,7 @@ pub fn complete_all(&self) {
     /// This method waits for the completion of a task; it is not interruptible and there is no
     /// timeout.
     ///
-    /// See also [`Completion::complete_all`].
+    /// See also [`Completion::complete`] and [`Completion::complete_all`].
     #[inline]
     pub fn wait_for_completion(&self) {
         // SAFETY: `self.as_raw()` is a pointer to a valid `struct completion`.

-- 
2.54.0