dt-bindings: net: Add bindings for LiteETH

LiteETH is a small footprint and configurable Ethernet core for FPGA
based system on chips.

The hardware is parametrised by the size and number of the slots in it's
receive and send buffers. These are described as properties, with the
commonly used values set as the default.
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/litex,liteeth.yaml

+# SPDX-License-Identifier: GPL-2.0-or-later OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/net/litex,liteeth.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: LiteX LiteETH ethernet device
+
+maintainers:
+  - Joel Stanley <joel@jms.id.au>
+
+description: |
+  LiteETH is a small footprint and configurable Ethernet core for FPGA based
+  system on chips.
+
+  The hardware source is Open Source and can be found on at
+  https://github.com/enjoy-digital/liteeth/.
+
+allOf:
+  - $ref: ethernet-controller.yaml#
+
+properties:
+  compatible:
+    const: litex,liteeth
+
+  reg:
+    items:
+      - description: MAC registers
+      - description: MDIO registers
+      - description: Packet buffer
+
+  reg-names:
+    items:
+      - const: mac
+      - const: mdio
+      - const: buffer
+
+  interrupts:
+    maxItems: 1
+
+  litex,rx-slots:
+    description: Number of slots in the receive buffer
+    $ref: /schemas/types.yaml#/definitions/uint32
+    minimum: 1
+    default: 2
+
+  litex,tx-slots:
+    description: Number of slots in the transmit buffer
+    $ref: /schemas/types.yaml#/definitions/uint32
+    minimum: 1
+    default: 2
+
+  litex,slot-size:
+    description: Size in bytes of a slot in the tx/rx buffer
+    $ref: /schemas/types.yaml#/definitions/uint32
+    minimum: 0x800
+    default: 0x800
+
+  mac-address: true
+  local-mac-address: true
+  phy-handle: true
+
+  mdio:
+    $ref: mdio.yaml#
+
+required:
+  - compatible
+  - reg
+  - interrupts
+
+additionalProperties: false
+
+examples:
+  - |
+    mac: ethernet@8020000 {
+        compatible = "litex,liteeth";
+        reg = <0x8021000 0x100>,
+              <0x8020800 0x100>,
+              <0x8030000 0x2000>;
+        reg-names = "mac", "mdio", "buffer";
+        litex,rx-slots = <2>;
+        litex,tx-slots = <2>;
+        litex,slot-size = <0x800>;
+        interrupts = <0x11 0x1>;
+        phy-handle = <&eth_phy>;
+
+        mdio {
+          #address-cells = <1>;
+          #size-cells = <0>;
+
+          eth_phy: ethernet-phy@0 {
+            reg = <0>;
+          };
+        };
+    };
+...
+
+#  vim: set ts=2 sw=2 sts=2 tw=80 et cc=80 ft=yaml :