Add device tree binding documentation for the Synopsys DesignWare
XPCS integrated on the Rockchip RK3568 SoC.

The XPCS is accessed over the APB3 bus and internally connected to
a Naneng Combo SerDes PHY.  It supports 1000BASE-X, SGMII, and
QSGMII modes, with four MII ports.

The binding describes:
- Required properties: compatible, reg, clocks, clock-names
- Optional properties: phys, phy-names, power-domains
- pcs-mii sub-nodes for each MII port (reg 0..3)

Signed-off-by: Coia Prant <coiaprant@gmail.com>
---
 .../bindings/net/pcs/rockchip-dwxpcs.yaml     | 126 ++++++++++++++++++
 1 file changed, 126 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/net/pcs/rockchip-dwxpcs.yaml

diff --git a/Documentation/devicetree/bindings/net/pcs/rockchip-dwxpcs.yaml b/Documentation/devicetree/bindings/net/pcs/rockchip-dwxpcs.yaml
new file mode 100644
index 0000000000000..14fadf67c793a
--- /dev/null
+++ b/Documentation/devicetree/bindings/net/pcs/rockchip-dwxpcs.yaml
@@ -0,0 +1,126 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/net/pcs/rockchip-dwxpcs.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Rockchip RK3568 Synopsys DesignWare Ethernet PCS
+
+maintainers:
+  - Coia Prant <coiaprant@gmail.com>
+
+description: |
+  Rockchip RK3568 SoC integrates a Synopsys DesignWare Ethernet Physical
+  Coding Sublayer (XPCS).
+  The PCS provides an interface between the Media Access Control (MAC)
+  and the Physical Medium Attachment (PMA) sublayer through a Media
+  Independent Interface (GMII).
+
+  The XPCS is accessed over the APB3 bus and internally connected to a
+  Naneng Combo SerDes PHY.
+  It supports 1000BASE-X, SGMII and QSGMII modes.
+
+  The block contains four MII ports (pcs-mii@0..3) that can be
+  individually enabled and routed to one of the Ethernet GMAC controllers
+  via the pcs-handle property in the MAC device tree node.
+
+properties:
+  compatible:
+    const: rockchip,rk3568-xpcs
+
+  '#address-cells':
+    const: 1
+
+  '#size-cells':
+    const: 0
+
+  reg:
+    description: |
+      Base address and size of the XPCS register space mapped over the
+      APB3 bus.
+    maxItems: 1
+
+  clocks:
+    description: |
+      Clock sources for the XPCS:
+      - csr: APB3 bus interface clock (clk_csr_i), required for register
+        access.
+      - eee: EEE clock (clk_eee_i), required for Energy Efficient
+        Ethernet (EEE) operation.
+    minItems: 2
+    maxItems: 2
+
+  clock-names:
+    items:
+      - const: csr
+      - const: eee
+
+  phys:
+    description: |
+      The phandle of SerDes PHY (Naneng Combo PHY) that provides
+      the serial lanes for 1000BASE-X / SGMII / QSGMII.
+      The SerDes must be powered on and initialised before any XPCS
+      register access.
+    maxItems: 1
+
+  phy-names:
+    const: serdes
+
+  power-domains:
+    description: |
+      Power domain for the XPCS.
+      On RK3568 this is typically the PD_PIPE power domain, which also
+      supplies the SerDes PHY.
+    maxItems: 1
+
+patternProperties:
+  "^pcs-mii@[0-3]$":
+    type: object
+    description: |
+      One of the four MII ports of the XPCS.
+      The port number is specified by the reg property (0..3).
+      The port is linked to an Ethernet MAC controller via the
+      pcs-handle property in the MAC's device tree node.
+
+    properties:
+      reg:
+        minimum: 0
+        maximum: 3
+        description: |
+          MII port number of PCS.
+
+      status: true
+
+    required:
+      - reg
+
+    additionalProperties: false
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - clock-names
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/rk3568-cru.h>
+    #include <dt-bindings/power/rk3568-power.h>
+
+    pcs@fda00000 {
+      compatible = "rockchip,rk3568-xpcs";
+      #address-cells = <1>;
+      #size-cells = <0>;
+      reg = <0x0 0xfda00000 0x0 0x200000>;
+      clocks = <&cru PCLK_XPCS>, <&cru CLK_XPCS_EEE>;
+      clock-names = "csr", "eee";
+      phys = <&combphy2 PHY_TYPE_SGMII>;
+      phy-names = "serdes";
+      power-domains = <&power RK3568_PD_PIPE>;
+
+      pcs-mii@0 {
+        reg = <0>;
+      };
+    };
-- 
2.47.3