realtek: hog the GS1900-24E external IC reset line

The GPIO line connecting to the reset signals of the GS1900-24E(A1)'s
external ICs (RTL8218B phys and RTL8231 expander) cannot be asserted by
the MDIO subsystem, as the reset is shared between busses.

To prevent users from accidentally asserting the reset line, a GPIO hog
is created to permanently de-assert the signal, reliably keeping the
phys and GPIO expanders on.

Signed-off-by: Sander Vanheule <sander@svanheule.net>

Author: svanheule

target/linux/realtek/dts/rtl8382_zyxel_gs1900-24e-a1.dts

@@ -8,6 +8,16 @@
 	model = "Zyxel GS1900-24E A1";
 };
 
+&gpio0 {
+	/* Shared between the main and aux MDIO busses */
+	mdio_reset {
+		gpio-hog;
+		gpios = <1 GPIO_ACTIVE_LOW>;
+		output-low;
+		line-name = "mdio-reset";
+	};
+};
+
 &mdio_bus0 {
 	EXTERNAL_PHY(0)
 	EXTERNAL_PHY(1)