dt-bindings: pinctrl: document polarfire soc iomux0 pinmux

On Polarfire SoC, iomux0 is responsible for routing functions to either
Multiprocessor Subsystem (MSS) IOs or to the FPGA fabric, where they
can either interface with custom RTL or be routed to the FPGA fabric's
IOs. Document it.

Reviewed-by: Rob Herring (Arm) <[e-mail]>
Signed-off-by: Conor Dooley <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

Documentation/devicetree/bindings/pinctrl/microchip,mpfs-pinctrl-iomux0.yaml

···
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/pinctrl/microchip,mpfs-pinctrl-iomux0.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Microchip PolarFire SoC iomux0
+
+maintainers:
+  - Conor Dooley <[e-mail]>
+
+description:
+  iomux0 is responsible for routing some functions to either the FPGA fabric,
+  or to MSSIOs. It only performs muxing, and has no IO configuration role, as
+  fabric IOs are configured separately and just routing a function to MSSIOs is
+  not sufficient for it to actually get mapped to an MSSIO, just makes it
+  possible.
+
+properties:
+  compatible:
+    oneOf:
+      - const: microchip,mpfs-pinctrl-iomux0
+      - items:
+          - const: microchip,pic64gx-pinctrl-iomux0
+          - const: microchip,mpfs-pinctrl-iomux0
+
+  reg:
+    maxItems: 1
+
+  pinctrl-use-default: true
+
+patternProperties:
+  '^mux-':
+    type: object
+    $ref: pinmux-node.yaml
+    additionalProperties: false
+
+    properties:
+      function:
+        description:
+          A string containing the name of the function to mux to the group.
+        enum: [ spi0, spi1, i2c0, i2c1, can0, can1, qspi, uart0, uart1, uart2,
+                uart3, uart4, mdio0, mdio1 ]
+
+      groups:
+        description:
+          An array of strings. Each string contains the name of a group.
+        items:
+          enum: [ spi0_fabric, spi0_mssio, spi1_fabric, spi1_mssio, i2c0_fabric,
+                  i2c0_mssio, i2c1_fabric, i2c1_mssio, can0_fabric, can0_mssio,
+                  can1_fabric, can1_mssio, qspi_fabric, qspi_mssio,
+                  uart0_fabric, uart0_mssio, uart1_fabric, uart1_mssio,
+                  uart2_fabric, uart2_mssio, uart3_fabric, uart3_mssio,
+                  uart4_fabric, uart4_mssio, mdio0_fabric, mdio0_mssio,
+                  mdio1_fabric, mdio1_mssio ]
+
+    required:
+      - function
+      - groups
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    soc {
+      #size-cells = <1>;
+      #address-cells = <1>;
+
+      pinctrl@200 {
+        compatible = "microchip,mpfs-pinctrl-iomux0";
+        reg = <0x200 0x4>;
+
+        mux-spi0-fabric {
+          function = "spi0";
+          groups = "spi0_fabric";
+        };
+
+        mux-spi1-mssio {
+          function = "spi1";
+          groups = "spi1_mssio";
+        };
+      };
+    };
+
+...

Documentation/devicetree/bindings/soc/microchip/microchip,mpfs-mss-top-sysreg.yaml

···
     items:
       - const: microchip,mpfs-mss-top-sysreg
       - const: syscon
+      - const: simple-mfd
 
   reg:
     maxItems: 1
+
+  '#address-cells':
+    const: 1
+
+  '#size-cells':
+    const: 1
 
   '#reset-cells':
     description:
···
       of PolarFire clock/reset IDs.
     const: 1
 
+  pinctrl@200:
+    type: object
+    $ref: /schemas/pinctrl/microchip,mpfs-pinctrl-iomux0.yaml
+
 required:
   - compatible
   - reg
···
 examples:
   - |
     syscon@20002000 {
-      compatible = "microchip,mpfs-mss-top-sysreg", "syscon";
+      compatible = "microchip,mpfs-mss-top-sysreg", "syscon", "simple-mfd";
       reg = <0x20002000 0x1000>;
       #reset-cells = <1>;
     };