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diff --git a/Documentation/devicetree/bindings/net/mdio-mux-mmioreg.yaml b/Documentation/devicetree/bindings/net/mdio-mux-mmioreg.yaml
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+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/net/mdio-mux-mmioreg.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Properties for an MDIO bus multiplexer controlled by a memory-mapped device
+
+maintainers:
+  - Andrew Lunn <andrew@lunn.ch>
+
+description: |+
+  This is a special case of a MDIO bus multiplexer.  A memory-mapped device,
+  like an FPGA, is used to control which child bus is connected.  The mdio-mux
+  node must be a child of the memory-mapped device.  The driver currently only
+  supports devices with 8, 16 or 32-bit registers.
+
+allOf:
+  - $ref: /schemas/net/mdio-mux.yaml#
+
+properties:
+  compatible:
+    items:
+      - const: mdio-mux-mmioreg
+      - const: mdio-mux
+
+  reg:
+    description: Contains the offset of the register that controls the bus
+      multiplexer. The size field in the 'reg' property is the size of register,
+      and must therefore be 1, 2, or 4.
+    maxItems: 1
+
+  mux-mask:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: Contains an eight-bit mask that specifies which bits in the
+      register control the actual bus multiplexer.  The 'reg' property of each
+      child mdio-mux node must be constrained by this mask.
+
+required:
+  - compatible
+  - reg
+  - mux-mask
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    mdio-mux@9 {
+        compatible = "mdio-mux-mmioreg", "mdio-mux";
+        mdio-parent-bus = <&xmdio0>;
+        #address-cells = <1>;
+        #size-cells = <0>;
+        reg = <9 1>; // BRDCFG1
+        mux-mask = <0x6>; // EMI2
+
+        mdio@0 {  // Slot 1 XAUI (FM2)
+            reg = <0>;
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            phy_xgmii_slot1: ethernet-phy@4 {
+                compatible = "ethernet-phy-ieee802.3-c45";
+                reg = <4>;
+            };
+        };
+
+        mdio@2 {  // Slot 2 XAUI (FM1)
+            reg = <2>;
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            ethernet-phy@4 {
+                compatible = "ethernet-phy-ieee802.3-c45";
+                reg = <4>;
+            };
+        };
+    };
+...