realtek: rtl838x: Instantiate auxiliary MDIO bus

Add a disabled node for the auxiliary MDIO bus, used to manage the
RTL8231 expanders. A simple-mfd parent node is added, at the same
(implied) address as the switch@1b000000 node, as the switch drivers
should anyway transistion to MFD subdivices at some point.

Additionally, two pinctrl-single node are added to allow the MDX pins to
be muxed correctly, in case the bootloader leaves these unconfigured.

Signed-off-by: Sander Vanheule <[email protected]>

target/linux/realtek/dts/rtl838x.dtsi

@@ -232,6 +232,42 @@
 		};
 	};
 
+	switchcore@1b000000 {
+		compatible = "syscon", "simple-mfd";
+		reg = <0x1b000000 0x20000>;
+
+		mdio_aux: mdio-aux {
+			compatible = "realtek,rtl8380-aux-mdio";
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			status = "disabled";
+
+			pinctrl-names = "default";
+			pinctrl-0 = <&mdio_aux_mdx>, <&aux_mode_mdio>;
+		};
+	};
+
+	pinmux@1b000144 {
+		compatible = "pinctrl-single";
+		reg = <0x1b000144 0x4>;
+
+		pinctrl-single,bit-per-mux;
+		pinctrl-single,register-width = <32>;
+		pinctrl-single,function-mask = <0x1>;
+		#pinctrl-cells = <2>;
+
+		/* I2C mode */
+		aux_mode_i2c: i2c-pins {
+			pinctrl-single,bits = <0x0 0x0 0x1>;
+		};
+
+		/* MDIO mode */
+		aux_mode_mdio: mdx-pins {
+			pinctrl-single,bits = <0x0 0x1 0x1>;
+		};
+	};
+
 	pinmux: pinmux@1b001000 {
 		compatible = "pinctrl-single";
 		reg = <0x1b001000 0x4>;
@@ -262,6 +298,26 @@
 		};
 	};
 
+	pinmux@1b00a0e0 {
+		compatible = "pinctrl-single";
+		reg = <0x1b00a0e0 0x4>;
+
+		pinctrl-single,bit-per-mux;
+		pinctrl-single,register-width = <32>;
+		pinctrl-single,function-mask = <0x1>;
+		#pinctrl-cells = <2>;
+
+		/* Use SoC GPIO 2/3 as GPIO */
+		mdio_aux_gpio: gpio-pins {
+			pinctrl-single,bits = <0x0 0x0 0x1>;
+		};
+
+		/* Use SoC GPIO 2/3 as MDC/MDIO */
+		mdio_aux_mdx: mdx-pins {
+			pinctrl-single,bits = <0x0 0x1 0x1>;
+		};
+	};
+
 	ethernet0: ethernet@1b00a300 {
 		compatible = "realtek,rtl838x-eth";
 		reg = <0x1b00a300 0x100>;

target/linux/realtek/rtl838x/config-6.6

@@ -130,7 +130,7 @@ CONFIG_MDIO_BUS=y
 CONFIG_MDIO_DEVICE=y
 CONFIG_MDIO_DEVRES=y
 CONFIG_MDIO_I2C=y
-# CONFIG_MDIO_REALTEK_OTTO_AUX is not set
+CONFIG_MDIO_REALTEK_OTTO_AUX=y
 CONFIG_MDIO_SMBUS=y
 CONFIG_MFD_SYSCON=y
 CONFIG_MIGRATION=y