arm64: dts: qcom: msm8916-samsung-a2015: Add touch key

The Samsung Galaxy A3/A5 both have two capacitive touch keys,
connected to an ABOV MCU. It implements the same interface as
implemented by the tm2-touchkey driver and works just fine with
the coreriver,tc360-touchkey compatible. It's probably actually some
Samsung-specific interface that they implement with different MCUs.

Note that for some reason Samsung decided to connect this to GPIOs
where no hardware I2C bus is available, so we need to fall back
to software bit-banging using i2c-gpio.

The vdd/vcc-supply is board-specific and will be added separately
for a3u/a5u.
Co-developed-by: Michael Srba <Michael.Srba@seznam.cz>
Signed-off-by: Michael Srba <Michael.Srba@seznam.cz>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20210604172742.10593-1-stephan@gerhold.netSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

arch/arm64/boot/dts/qcom/msm8916-samsung-a2015-common.dtsi

@@ -95,6 +95,35 @@ muic: extcon@25 {
 			pinctrl-0 = <&muic_int_default>;
 		};
 	};
+
+	i2c-tkey {
+		compatible = "i2c-gpio";
+		sda-gpios = <&msmgpio 16 (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN)>;
+		scl-gpios = <&msmgpio 17 (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN)>;
+
+		pinctrl-names = "default";
+		pinctrl-0 = <&tkey_i2c_default>;
+
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		touchkey: touchkey@20 {
+			/* Note: Actually an ABOV MCU that implements same interface */
+			compatible = "coreriver,tc360-touchkey";
+			reg = <0x20>;
+
+			interrupt-parent = <&msmgpio>;
+			interrupts = <98 IRQ_TYPE_EDGE_FALLING>;
+
+			/* vcc/vdd-supply are board-specific */
+			vddio-supply = <&pm8916_l6>;
+
+			linux,keycodes = <KEY_APPSELECT KEY_BACK>;
+
+			pinctrl-names = "default";
+			pinctrl-0 = <&tkey_default>;
+		};
+	};
 };
 
 &blsp_i2c2 {
@@ -333,6 +362,22 @@ muic_int_default: muic-int-default {
 		bias-disable;
 	};
 
+	tkey_default: tkey-default {
+		pins = "gpio98";
+		function = "gpio";
+
+		drive-strength = <2>;
+		bias-disable;
+	};
+
+	tkey_i2c_default: tkey-i2c-default {
+		pins = "gpio16", "gpio17";
+		function = "gpio";
+
+		drive-strength = <2>;
+		bias-disable;
+	};
+
 	tsp_en_default: tsp-en-default {
 		pins = "gpio73";
 		function = "gpio";