ARM64: dts: meson-axg: add adc buttons the S400

Add the 6 adc buttons of the amlogic S400
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

arch/arm64/boot/dts/amlogic/meson-axg-s400.dts

@@ -6,11 +6,55 @@
 /dts-v1/;
 
 #include "meson-axg.dtsi"
+#include <dt-bindings/input/input.h>
 
 / {
 	compatible = "amlogic,s400", "amlogic,a113d", "amlogic,meson-axg";
 	model = "Amlogic Meson AXG S400 Development Board";
 
+	adc_keys {
+		compatible = "adc-keys";
+		io-channels = <&saradc 0>;
+		io-channel-names = "buttons";
+		keyup-threshold-microvolt = <1800000>;
+
+		button-next {
+			label = "Next";
+			linux,code = <KEY_NEXT>;
+			press-threshold-microvolt = <1116000>; /* 62% */
+		};
+
+		button-prev {
+			label = "Previous";
+			linux,code = <KEY_PREVIOUS>;
+			press-threshold-microvolt = <900000>; /* 50% */
+		};
+
+		button-wifi {
+			label = "Wifi";
+			linux,code = <KEY_WLAN>;
+			press-threshold-microvolt = <684000>; /* 38% */
+		};
+
+		button-up {
+			label = "Volume Up";
+			linux,code = <KEY_VOLUMEUP>;
+			press-threshold-microvolt = <468000>; /* 26% */
+		};
+
+		button-down {
+			label = "Volume Down";
+			linux,code = <KEY_VOLUMEDOWN>;
+			press-threshold-microvolt = <252000>; /* 14% */
+		};
+
+		button-voice {
+			label = "Voice";
+			linux,code = <KEY_VOICECOMMAND>;
+			press-threshold-microvolt = <0>; /* 0% */
+		};
+	};
+
 	aliases {
 		serial0 = &uart_AO;
 		serial1 = &uart_A;