arm64: dts: rockchip: Add support for volume keys to rk3399-pinephone-pro

These are implemented via regular ADC, so regular polling is needed,
for these keys to work.

Co-developed-by: Martijn Braam <martijn@brixit.nl>
Signed-off-by: Martijn Braam <martijn@brixit.nl>
Co-developed-by: Kamil Trzciński <ayufan@ayufan.eu>
Signed-off-by: Kamil Trzciński <ayufan@ayufan.eu>
Signed-off-by: Ondrej Jirman <megi@xff.cz>
Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Tested-by: Ondrej Jirman <megi@xff.cz>
Link: https://lore.kernel.org/r/20230405123813.2272919-1-pbrobinson@gmail.com
[increased Volume-Down voltage to 600mV as suggested by Ondrej]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

Author: Ondrej Jirman

arch/arm64/boot/dts/rockchip/rk3399-pinephone-pro.dts

@@ -10,6 +10,7 @@
  */
 
 /dts-v1/;
+#include <dt-bindings/input/gpio-keys.h>
 #include <dt-bindings/input/linux-event-codes.h>
 #include "rk3399.dtsi"
 #include "rk3399-opp.dtsi"
@@ -29,6 +30,26 @@
 		stdout-path = "serial2:115200n8";
 	};
 
+	adc-keys {
+		compatible = "adc-keys";
+		io-channels = <&saradc 1>;
+		io-channel-names = "buttons";
+		keyup-threshold-microvolt = <1600000>;
+		poll-interval = <100>;
+
+		button-up {
+			label = "Volume Up";
+			linux,code = <KEY_VOLUMEUP>;
+			press-threshold-microvolt = <100000>;
+		};
+
+		button-down {
+			label = "Volume Down";
+			linux,code = <KEY_VOLUMEDOWN>;
+			press-threshold-microvolt = <600000>;
+		};
+	};
+
 	backlight: backlight {
 		compatible = "pwm-backlight";
 		pwms = <&pwm0 0 50000 0>;
@@ -519,6 +540,11 @@
 	status = "okay";
 };
 
+&saradc {
+	vref-supply = <&vcca1v8_s3>;
+	status = "okay";
+};
+
 &sdmmc {
 	bus-width = <4>;
 	cap-sd-highspeed;