Add ads7846 touch screen for WaveShare 4"/3.5" HDMI LCD

Please note that waveshare35a-tinker/waveshare32b-tinker
dts overlay use the same touch IC but different interrupt pin,
so please never use them at the same time.

Change-Id: I449f9d905010d65b4268011e406b827d91f258bf
Reviewed-on: https://tp-biosrd-v02/gerrit/82275
Reviewed-by: Scorpio Chang(張志賢) <Scorpio_Chang@asus.com>
Tested-by: Scorpio Chang(張志賢) <Scorpio_Chang@asus.com>

Author: yc-hou-0919

arch/arm/boot/dts/overlays/Makefile

@@ -21,7 +21,7 @@ dtbo-$(CONFIG_ARCH_ROCKCHIP) += \
 	lirc-toshiba.dtbo \
 	mcp2515-can0.dtbo \
 	googlevoicehat-soundcard.dtbo \
-
+	ads7846-tinker.dtbo \
 
 targets += dtbs dtbs_install
 targets += $(dtbo-y)

arch/arm/boot/dts/overlays/ads7846-tinker-overlay.dts

@@ -0,0 +1,78 @@
+/*
+ * Generic Device Tree overlay for the ADS7846 touch controller
+ *
+ */
+
+/dts-v1/;
+/plugin/;
+
+/ {
+	compatible = "rockchip,rk3288-miniarm", "rockchip,rk3288";
+
+        fragment@0 {
+                target = <&spi2>;
+
+                __overlay__ {
+                        status = "okay";
+
+                        spidev@0 {
+                                status = "disabled";
+                        };
+
+                        spidev@1 {
+                                status = "disabled";
+                        };
+                };
+        };
+
+	fragment@1 {
+		target = <&gpio5>;
+		__overlay__ {
+			ads7846_pins: ads7846_pins {
+				rockchip,pins = <5 19 0 &pcfg_pull_up>;
+			};
+		};
+	};
+
+	fragment@2 {
+		target = <&spi2>;
+		__overlay__ {
+			/* needed to avoid dtc warning */
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			ads7846: ads7846@1 {
+				compatible = "ti,ads7846";
+				reg = <1>;			
+				pinctrl-names = "default";
+                                pinctrl-0 = <&ads7846_pins>;
+
+				spi-max-frequency = <2000000>;
+				interrupts = <19 2>; // high-to-low edge triggered
+                                interrupt-parent = <&gpio5>;
+				pendown-gpio = <&gpio5 19 0>;
+				ti,x-plate-ohms = /bits/ 16 <60>;
+				ti,pressure-max = /bits/ 16 <255>;
+			};
+		};
+	};
+
+/*
+	__overrides__ {
+		cs =     <&ads7846>,"reg:0";
+		speed =  <&ads7846>,"spi-max-frequency:0";
+		penirq = <&ads7846_pins>,"brcm,pins:0", // REQUIRED 
+			 <&ads7846>,"interrupts:0",
+			 <&ads7846>,"pendown-gpio:4";
+		penirq_pull = <&ads7846_pins>,"brcm,pull:0";
+		swapxy = <&ads7846>,"ti,swap-xy?";
+		xmin =   <&ads7846>,"ti,x-min;0";
+		ymin =   <&ads7846>,"ti,y-min;0";
+		xmax =   <&ads7846>,"ti,x-max;0";
+		ymax =   <&ads7846>,"ti,y-max;0";
+		pmin =   <&ads7846>,"ti,pressure-min;0";
+		pmax =   <&ads7846>,"ti,pressure-max;0";
+		xohms =  <&ads7846>,"ti,x-plate-ohms;0";
+	};
+*/
+};