realtek: rtl839x: Enable AUX MDIO controller

Enable the driver for the Realtek Otto auxiliary MDIO driver so RTL839x
devices can use it. The related node is added to the base devicetree for
rtl839x-based devices, so they can enabled and use it when required.

Signed-off-by: Sander Vanheule <[email protected]>
(cherry picked from commit cddcc69ddf9c6284d6c9a6399c4ea48d7a044719)

target/linux/realtek/dts/rtl839x.dtsi

@@ -258,6 +258,22 @@
 
 	};
 
+	switchcore@1b000000 {
+		compatible = "syscon", "simple-mfd";
+		reg = <0x1b000000 0x20000>;
+
+		mdio_aux: mdio-aux {
+			compatible = "realtek,rtl8390-aux-mdio";
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			status = "disabled";
+
+			pinctrl-names = "default";
+			pinctrl-0 = <&mdio_aux_mdx>;
+		};
+	};
+
 	pinmux@1b000004 {
 		compatible = "pinctrl-single";
 		reg = <0x1b000004 0x4>;
@@ -290,6 +306,11 @@
 		pinmux_disable_sys_led: disable_sys_led {
 			pinctrl-single,bits = <0x0 0x0 0x4000>;
 		};
+
+		/* enable AUX MDC/MDIO */
+		mdio_aux_mdx: aux-mdx-pins {
+			pinctrl-single,bits = <0x0 0x100000 0x1c0000>;
+		};
 	};
 
 	ethernet0: ethernet@1b00a300 {

target/linux/realtek/rtl839x/config-6.6

@@ -121,7 +121,7 @@ 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_MEMFD_CREATE=y
 # CONFIG_MFD_RTL8231 is not set