Enable the SARADC controller and add the adc-keys node to support
the Function key found on the Khadas VIM1S board.

Signed-off-by: Nick Xie <nick@khadas.com>
---
 .../amlogic/meson-s4-s905y4-khadas-vim1s.dts  | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/arm64/boot/dts/amlogic/meson-s4-s905y4-khadas-vim1s.dts b/arch/arm64/boot/dts/amlogic/meson-s4-s905y4-khadas-vim1s.dts
index cf65c079e675a..2fa2ed941cb98 100644
--- a/arch/arm64/boot/dts/amlogic/meson-s4-s905y4-khadas-vim1s.dts
+++ b/arch/arm64/boot/dts/amlogic/meson-s4-s905y4-khadas-vim1s.dts
@@ -40,6 +40,20 @@ secmon_reserved: secmon@5000000 {
 		};
 	};
 
+	adc-keys {
+		compatible = "adc-keys";
+		io-channels = <&saradc 0>;
+		io-channel-names = "buttons";
+		keyup-threshold-microvolt = <1710000>;
+		poll-interval = <100>;
+
+		button-function {
+			label = "Function";
+			linux,code = <KEY_FN>;
+			press-threshold-microvolt = <10000>;
+		};
+	};
+
 	emmc_pwrseq: emmc-pwrseq {
 		compatible = "mmc-pwrseq-emmc";
 		reset-gpios = <&gpio GPIOB_9 GPIO_ACTIVE_LOW>;
@@ -278,6 +292,11 @@ brcmf: wifi@1 {
 	};
 };
 
+&saradc {
+	status = "okay";
+	vref-supply = <&vddio_ao1v8>;
+};
+
 &spicc0 {
 	status = "okay";
 	pinctrl-names = "default";
-- 
2.34.1