1 files changed, 37 insertions, 0 deletions
diff --git a/rust/kernel/time/delay.rs b/rust/kernel/time/delay.rs
index eb8838da62bc..b5b1b42797a0 100644
--- a/rust/kernel/time/delay.rs
+++ b/rust/kernel/time/delay.rs
@@ -47,3 +47,40 @@ pub fn fsleep(delta: Delta) {
         bindings::fsleep(delta.as_micros_ceil() as c_ulong)
     }
 }
+
+/// Inserts a delay based on microseconds with busy waiting.
+///
+/// Equivalent to the C side [`udelay()`], which delays in microseconds.
+///
+/// `delta` must be within `[0, MAX_UDELAY_MS]` in milliseconds;
+/// otherwise, it is erroneous behavior. That is, it is considered a bug to
+/// call this function with an out-of-range value.
+///
+/// The behavior above differs from the C side [`udelay()`] for which out-of-range
+/// values could lead to an overflow and unexpected behavior.
+///
+/// [`udelay()`]: https://docs.kernel.org/timers/delay_sleep_functions.html#c.udelay
+pub fn udelay(delta: Delta) {
+    const MAX_UDELAY_DELTA: Delta = Delta::from_millis(bindings::MAX_UDELAY_MS as i64);
+
+    debug_assert!(delta.as_nanos() >= 0);
+    debug_assert!(delta <= MAX_UDELAY_DELTA);
+
+    let delta = if (Delta::ZERO..=MAX_UDELAY_DELTA).contains(&delta) {
+        delta
+    } else {
+        MAX_UDELAY_DELTA
+    };
+
+    // SAFETY: It is always safe to call `udelay()` with any duration.
+    // Note that the kernel is compiled with `-fno-strict-overflow`
+    // so any out-of-range value could lead to unexpected behavior
+    // but won't lead to undefined behavior.
+    unsafe {
+        // Convert the duration to microseconds and round up to preserve
+        // the guarantee; `udelay()` inserts a delay for at least
+        // the provided duration, but that it may delay for longer
+        // under some circumstances.
+        bindings::udelay(delta.as_micros_ceil() as c_ulong)
+    }
+}