diff --git a/Documentation/devicetree/bindings/opp/opp.txt b/Documentation/devicetree/bindings/opp/opp.txt
index 788052d66c9d5f45f689623761e50969ab0c6f5a..c396c4c0af92db1faa8d0f7ee7fe44b6a7fac242 100644
--- a/Documentation/devicetree/bindings/opp/opp.txt
+++ b/Documentation/devicetree/bindings/opp/opp.txt
@@ -82,7 +82,10 @@ This defines voltage-current-frequency combinations along with other related
 properties.
 
 Required properties:
-- opp-hz: Frequency in Hz, expressed as a 64-bit big-endian integer.
+- opp-hz: Frequency in Hz, expressed as a 64-bit big-endian integer. This is a
+  required property for all device nodes but devices like power domains. The
+  power domain nodes must have another (implementation dependent) property which
+  uniquely identifies the OPP nodes.
 
 Optional properties:
 - opp-microvolt: voltage in micro Volts.