The Realtek Otto Switch ethernet MDIO controller supports different MDC
speeds ranging from 1.25MHz to 10MHz. Document the clock-frequency
attribute for the device tree.

There is neither an official documentation nor any obvious registers that
indicate a dependency to one of the hardware clocks. The usable setup bits
are more like hardcoded values than dividers. Without further details do
not add a clock reference.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
---
 .../bindings/net/realtek,rtl9301-mdio.yaml    | 40 +++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/Documentation/devicetree/bindings/net/realtek,rtl9301-mdio.yaml b/Documentation/devicetree/bindings/net/realtek,rtl9301-mdio.yaml
index 67e0b23a8470..88502d017eed 100644
--- a/Documentation/devicetree/bindings/net/realtek,rtl9301-mdio.yaml
+++ b/Documentation/devicetree/bindings/net/realtek,rtl9301-mdio.yaml
@@ -56,6 +56,9 @@ patternProperties:
       reg:
         maxItems: 1
 
+      clock-frequency:
+        default: 2500000
+
     required:
       - reg
 
@@ -71,6 +74,43 @@ required:
   - compatible
   - reg
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - realtek,rtl8380-mdio
+              - realtek,rtl8381-mdio
+              - realtek,rtl8382-mdio
+    then:
+      patternProperties:
+        '^mdio-bus@[0-3]$':
+          properties:
+            clock-frequency:
+              enum: [2500000, 10000000]
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - realtek,rtl8391-mdio
+              - realtek,rtl8392-mdio
+              - realtek,rtl8393-mdio
+              - realtek,rtl9301-mdio
+              - realtek,rtl9302b-mdio
+              - realtek,rtl9302c-mdio
+              - realtek,rtl9303-mdio
+              - realtek,rtl9311-mdio
+              - realtek,rtl9312-mdio
+              - realtek,rtl9313-mdio
+    then:
+      patternProperties:
+        '^mdio-bus@[0-3]$':
+          properties:
+            clock-frequency:
+              enum: [1250000, 2500000, 5000000]
+
 unevaluatedProperties: false
 
 examples:
-- 
2.55.0