diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 05f6df1fdf5bbfc70880f188c40e61264f764cc7..7770676c387a66cec9a8a3d8333bfa6e1e56ffe8 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -418,7 +418,22 @@ static inline int hrtimer_callback_running(struct hrtimer *timer)
 extern u64
 hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval);
 
-/* Forward a hrtimer so it expires after the hrtimer's current now */
+/**
+ * hrtimer_forward_now - forward the timer expiry so it expires after now
+ * @timer:	hrtimer to forward
+ * @interval:	the interval to forward
+ *
+ * Forward the timer expiry so it will expire after the current time
+ * of the hrtimer clock base. Returns the number of overruns.
+ *
+ * Can be safely called from the callback function of @timer. If
+ * called from other contexts @timer must neither be enqueued nor
+ * running the callback and the caller needs to take care of
+ * serialization.
+ *
+ * Note: This only updates the timer expiry value and does not requeue
+ * the timer.
+ */
 static inline u64 hrtimer_forward_now(struct hrtimer *timer,
 				      ktime_t interval)
 {
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 76d4bd962b19b3bab345460676954ef6f7c14568..b1a74ee3e99afd19acc0e581b695a8cc8475fbb3 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -801,6 +801,14 @@ void unlock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
  *
  * Forward the timer expiry so it will expire in the future.
  * Returns the number of overruns.
+ *
+ * Can be safely called from the callback function of @timer. If
+ * called from other contexts @timer must neither be enqueued nor
+ * running the callback and the caller needs to take care of
+ * serialization.
+ *
+ * Note: This only updates the timer expiry value and does not requeue
+ * the timer.
  */
 u64 hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval)
 {