dt-bindings: net: Add a YAML schemas for the generic MDIO options

The MDIO buses have a number of available device tree properties that can
be used in their device tree node. Add a YAML schemas for those.

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/net/mdio.yaml

@@ -0,0 +1,51 @@
+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/net/mdio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MDIO Bus Generic Binding
+
+maintainers:
+  - Andrew Lunn <andrew@lunn.ch>
+  - Florian Fainelli <f.fainelli@gmail.com>
+  - Heiner Kallweit <hkallweit1@gmail.com>
+
+description:
+  These are generic properties that can apply to any MDIO bus. Any
+  MDIO bus must have a list of child nodes, one per device on the
+  bus. These should follow the generic ethernet-phy.yaml document, or
+  a device specific binding document.
+
+properties:
+  reset-gpios:
+    maxItems: 1
+    description:
+      The phandle and specifier for the GPIO that controls the RESET
+      lines of all PHYs on that MDIO bus.
+
+  reset-delay-us:
+    description:
+      RESET pulse width in microseconds. It applies to all PHY devices
+      and must therefore be appropriately determined based on all PHY
+      requirements (maximum value of all per-PHY RESET pulse widths).
+
+examples:
+  - |
+    davinci_mdio: mdio@5c030000 {
+        compatible = "ti,davinci_mdio";
+        reg = <0x5c030000 0x1000>;
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        reset-gpios = <&gpio2 5 1>;
+        reset-delay-us = <2>;
+
+        ethphy0: ethernet-phy@1 {
+            reg = <1>;
+        };
+
+        ethphy1: ethernet-phy@3 {
+            reg = <3>;
+        };
+    };