diff --git a/target/linux/realtek/dts/rtl839x.dtsi b/target/linux/realtek/dts/rtl839x.dtsi
index 3f87f5622e2..7fc5aea70c4 100644
--- a/target/linux/realtek/dts/rtl839x.dtsi
+++ b/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 {
diff --git a/target/linux/realtek/rtl839x/config-6.6 b/target/linux/realtek/rtl839x/config-6.6
index 2616286a172..dac76469255 100644
--- a/target/linux/realtek/rtl839x/config-6.6
+++ b/target/linux/realtek/rtl839x/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_RTL8231 is not set
 CONFIG_MFD_SYSCON=y