diff --git a/Documentation/devicetree/bindings/mailbox/rockchip-mailbox.txt b/Documentation/devicetree/bindings/mailbox/rockchip-mailbox.txt
index aba0813f1054..c3a5be01c1e4 100644
--- a/Documentation/devicetree/bindings/mailbox/rockchip-mailbox.txt
+++ b/Documentation/devicetree/bindings/mailbox/rockchip-mailbox.txt
@@ -20,6 +20,7 @@ Required properties:
 Optional properties :
 
  - wakeup-source: Mailbox irq can be used as a wakeup source.
+ - rockchip,txpoll-period-ms: TX Done polling interval in milliseconds.
 
 Example:
 --------