diff --git a/Documentation/devicetree/bindings/arm/mediatek/mediatek,sgmiisys.txt b/Documentation/devicetree/bindings/arm/mediatek/mediatek,sgmiisys.txt
index 30cb645c0e5483a35206f9495df0ba787ea04940..f5518f26a91440a549250f976de2e2395e41ed1d 100644
--- a/Documentation/devicetree/bindings/arm/mediatek/mediatek,sgmiisys.txt
+++ b/Documentation/devicetree/bindings/arm/mediatek/mediatek,sgmiisys.txt
@@ -9,6 +9,8 @@ Required Properties:
 	- "mediatek,mt7622-sgmiisys", "syscon"
 	- "mediatek,mt7629-sgmiisys", "syscon"
 - #clock-cells: Must be 1
+- mediatek,physpeed: Should be one of "auto", "1000" or "2500" to match up
+		     the capability of the target PHY.
 
 The SGMIISYS controller uses the common clk binding from
 Documentation/devicetree/bindings/clock/clock-bindings.txt