dt-bindings: phy: realtek: Add Realtek DHC RTD SoC USB 2.0 PHY

Document the USB PHY bindings for Realtek SoCs.
Realtek DHC (digital home center) RTD SoCs support DWC3 XHCI USB
controller and using USB 2.0 PHY transceiver.
Signed-off-by: Stanley Chang <stanley_chang@realtek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230725033318.8361-4-stanley_chang@realtek.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/phy/realtek,usb2phy.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+# Copyright 2023 Realtek Semiconductor Corporation
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/phy/realtek,usb2phy.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Realtek DHC SoCs USB 2.0 PHY
+
+maintainers:
+  - Stanley Chang <stanley_chang@realtek.com>
+
+description: |
+  Realtek USB 2.0 PHY support the digital home center (DHC) RTD series SoCs.
+  The USB 2.0 PHY driver is designed to support the XHCI controller. The SoCs
+  support multiple XHCI controllers. One PHY device node maps to one XHCI
+  controller.
+
+  RTD1295/RTD1619 SoCs USB
+  The USB architecture includes three XHCI controllers.
+  Each XHCI maps to one USB 2.0 PHY and map one USB 3.0 PHY on some
+  controllers.
+  XHCI controller#0 -- usb2phy -- phy#0
+                    |- usb3phy -- phy#0
+  XHCI controller#1 -- usb2phy -- phy#0
+  XHCI controller#2 -- usb2phy -- phy#0
+                    |- usb3phy -- phy#0
+
+  RTD1395 SoCs USB
+  The USB architecture includes two XHCI controllers.
+  The controller#0 has one USB 2.0 PHY. The controller#1 includes two USB 2.0
+  PHY.
+  XHCI controller#0 -- usb2phy -- phy#0
+  XHCI controller#1 -- usb2phy -- phy#0
+                               |- phy#1
+
+  RTD1319/RTD1619b SoCs USB
+  The USB architecture includes three XHCI controllers.
+  Each XHCI maps to one USB 2.0 PHY and map one USB 3.0 PHY on controllers#2.
+  XHCI controller#0 -- usb2phy -- phy#0
+  XHCI controller#1 -- usb2phy -- phy#0
+  XHCI controller#2 -- usb2phy -- phy#0
+                    |- usb3phy -- phy#0
+
+  RTD1319d SoCs USB
+  The USB architecture includes three XHCI controllers.
+  Each xhci maps to one USB 2.0 PHY and map one USB 3.0 PHY on controllers#0.
+  XHCI controller#0 -- usb2phy -- phy#0
+                    |- usb3phy -- phy#0
+  XHCI controller#1 -- usb2phy -- phy#0
+  XHCI controller#2 -- usb2phy -- phy#0
+
+  RTD1312c/RTD1315e SoCs USB
+  The USB architecture includes three XHCI controllers.
+  Each XHCI maps to one USB 2.0 PHY.
+  XHCI controller#0 -- usb2phy -- phy#0
+  XHCI controller#1 -- usb2phy -- phy#0
+  XHCI controller#2 -- usb2phy -- phy#0
+
+properties:
+  compatible:
+    enum:
+      - realtek,rtd1295-usb2phy
+      - realtek,rtd1312c-usb2phy
+      - realtek,rtd1315e-usb2phy
+      - realtek,rtd1319-usb2phy
+      - realtek,rtd1319d-usb2phy
+      - realtek,rtd1395-usb2phy
+      - realtek,rtd1395-usb2phy-2port
+      - realtek,rtd1619-usb2phy
+      - realtek,rtd1619b-usb2phy
+
+  reg:
+    items:
+      - description: PHY data registers
+      - description: PHY control registers
+
+  "#phy-cells":
+    const: 0
+
+  nvmem-cells:
+    maxItems: 2
+    description:
+      Phandles to nvmem cell that contains the trimming data.
+      If unspecified, default value is used.
+
+  nvmem-cell-names:
+    items:
+      - const: usb-dc-cal
+      - const: usb-dc-dis
+    description:
+      The following names, which correspond to each nvmem-cells.
+      usb-dc-cal is the driving level for each phy specified via efuse.
+      usb-dc-dis is the disconnection level for each phy specified via efuse.
+
+  realtek,inverse-hstx-sync-clock:
+    description:
+      For one of the phys of RTD1619b SoC, the synchronous clock of the
+      high-speed tx must be inverted.
+    type: boolean
+
+  realtek,driving-level:
+    description:
+      Control the magnitude of High speed Dp/Dm output swing (mV).
+      For a different board or port, the original magnitude maybe not meet
+      the specification. In this situation we can adjust the value to meet
+      the specification.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    default: 8
+    minimum: 0
+    maximum: 31
+
+  realtek,driving-level-compensate:
+    description:
+      For RTD1315e SoC, the driving level can be adjusted by reading the
+      efuse table. This property provides drive compensation.
+      If the magnitude of High speed Dp/Dm output swing still not meet the
+      specification, then we can set this value to meet the specification.
+    $ref: /schemas/types.yaml#/definitions/int32
+    default: 0
+    minimum: -8
+    maximum: 8
+
+  realtek,disconnection-compensate:
+    description:
+      This adjusts the disconnection level compensation for the different
+      boards with different disconnection level.
+    $ref: /schemas/types.yaml#/definitions/int32
+    default: 0
+    minimum: -8
+    maximum: 8
+
+required:
+  - compatible
+  - reg
+  - "#phy-cells"
+
+allOf:
+  - if:
+      not:
+        properties:
+          compatible:
+            contains:
+              enum:
+                - realtek,rtd1619b-usb2phy
+    then:
+      properties:
+        realtek,inverse-hstx-sync-clock: false
+
+  - if:
+      not:
+        properties:
+          compatible:
+            contains:
+              enum:
+                - realtek,rtd1315e-usb2phy
+    then:
+      properties:
+        realtek,driving-level-compensate: false
+
+additionalProperties: false
+
+examples:
+  - |
+    usb-phy@13214 {
+        compatible = "realtek,rtd1619b-usb2phy";
+        reg = <0x13214 0x4>, <0x28280 0x4>;
+        #phy-cells = <0>;
+        nvmem-cells = <&otp_usb_port0_dc_cal>, <&otp_usb_port0_dc_dis>;
+        nvmem-cell-names = "usb-dc-cal", "usb-dc-dis";
+
+        realtek,inverse-hstx-sync-clock;
+        realtek,driving-level = <0xa>;
+        realtek,disconnection-compensate = <(-1)>;
+    };