--- zzzz-none-000/linux-4.4.60/Documentation/devicetree/bindings/serial/qcom,msm-uart.txt	2017-04-08 07:53:53.000000000 +0000
+++ wasp-540e-714/linux-4.4.60/Documentation/devicetree/bindings/serial/qcom,msm-uart.txt	2019-07-03 09:21:34.000000000 +0000
@@ -12,6 +12,10 @@
 - clocks: Should contain the core clock.
 - clock-names: Should be "core".
 
+Optional properties:
+- serial_clk: Required to set the clock rate when its not passing from boot
+            loader such as u-boot.
+
 Example:
 
 A uart device at 0xa9c00000 with interrupt 11.