diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 8bd383c..0f96646 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2020,8 +2020,13 @@
 /**
  * skb_complete_tx_timestamp() - deliver cloned skb with tx timestamps
  *
+ * PHY drivers may accept clones of transmitted packets for
+ * timestamping via their phy_driver.txtstamp method. These drivers
+ * must call this function to return the skb back to the stack, with
+ * or without a timestamp.
+ *
  * @skb: clone of the the original outgoing packet
- * @hwtstamps: hardware time stamps
+ * @hwtstamps: hardware time stamps, may be NULL if not available
  *
  */
 void skb_complete_tx_timestamp(struct sk_buff *skb,