dt-bindings: net: dsa: Add DSA yaml binding

For future DSA drivers it makes sense to add a generic DSA yaml binding which
can be used then. This was created using the properties from dsa.txt. It
includes the ports and the dsa,member property.
Suggested-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/dsa/dsa.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/net/dsa/dsa.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Ethernet Switch Device Tree Bindings
+
+maintainers:
+  - Andrew Lunn <andrew@lunn.ch>
+  - Florian Fainelli <f.fainelli@gmail.com>
+  - Vivien Didelot <vivien.didelot@gmail.com>
+
+description:
+  This binding represents Ethernet Switches which have a dedicated CPU
+  port. That port is usually connected to an Ethernet Controller of the
+  SoC. Such setups are typical for embedded devices.
+
+select: false
+
+properties:
+  $nodename:
+    pattern: "^switch(@.*)?$"
+
+  dsa,member:
+    minItems: 2
+    maxItems: 2
+    description:
+      A two element list indicates which DSA cluster, and position within the
+      cluster a switch takes. <0 0> is cluster 0, switch 0. <0 1> is cluster 0,
+      switch 1. <1 0> is cluster 1, switch 0. A switch not part of any cluster
+      (single device hanging off a CPU port) must not specify this property
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+
+patternProperties:
+  "^(ethernet-)?ports$":
+    type: object
+    properties:
+      '#address-cells':
+        const: 1
+      '#size-cells':
+        const: 0
+
+    patternProperties:
+      "^(ethernet-)?port@[0-9]+$":
+        type: object
+        description: Ethernet switch ports
+
+        properties:
+          reg:
+            description: Port number
+
+          label:
+            description:
+              Describes the label associated with this port, which will become
+              the netdev name
+            $ref: /schemas/types.yaml#definitions/string
+
+          link:
+            description:
+              Should be a list of phandles to other switch's DSA port. This
+              port is used as the outgoing port towards the phandle ports. The
+              full routing information must be given, not just the one hop
+              routes to neighbouring switches
+            $ref: /schemas/types.yaml#definitions/phandle-array
+
+          ethernet:
+            description:
+              Should be a phandle to a valid Ethernet device node.  This host
+              device is what the switch port is connected to
+            $ref: /schemas/types.yaml#definitions/phandle
+
+          phy-handle: true
+
+          phy-mode: true
+
+          fixed-link: true
+
+          mac-address: true
+
+        required:
+          - reg
+
+        additionalProperties: false
+
+oneOf:
+  - required:
+    - ports
+  - required:
+    - ethernet-ports
+
+...