Input: add support for Elan eKTH I2C touchscreens

This driver supports Elan eKTH I2C touchscreen controllers. Note that these
are using custom protocol, as opposed to other Elan parts that use
HID-over-I2C and are supported by the standard HID-multitouch driver.
Signed-off-by: Scott Liu <scott.liu@emc.com.tw>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/elants_i2c.txt

+Elantech I2C Touchscreen
+
+Required properties:
+- compatible: must be "elan,ekth3500".
+- reg: I2C address of the chip.
+- interrupt-parent: a phandle for the interrupt controller (see interrupt
+  binding[0]).
+- interrupts: interrupt to which the chip is connected (see interrupt
+  binding[0]).
+
+Optional properties:
+- wakeup-source: touchscreen can be used as a wakeup source.
+- pinctrl-names: should be "default" (see pinctrl binding [1]).
+- pinctrl-0: a phandle pointing to the pin settings for the device (see
+  pinctrl binding [1]).
+
+[0]: Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
+[1]: Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
+
+Example:
+	&i2c1 {
+		/* ... */
+
+		touchscreen@10 {
+			compatible = "elan,ekth3500";
+			reg = <0x10>;
+			interrupt-parent = <&gpio4>;
+			interrupts = <0x0 IRQ_TYPE_EDGE_FALLING>;
+			wakeup-source;
+		};
+
+		/* ... */
+	};

drivers/input/touchscreen/Kconfig

@@ -347,6 +347,18 @@ config TOUCHSCREEN_GUNZE
 	  To compile this driver as a module, choose M here: the
 	  module will be called gunze.
 
+config TOUCHSCREEN_ELAN
+	tristate "Elan eKTH I2C touchscreen"
+	depends on I2C
+	help
+	  Say Y here if you have an Elan eKTH I2C touchscreen
+	  connected to your system.
+
+	  If unsure, say N.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called elants_i2c.
+
 config TOUCHSCREEN_ELO
 	tristate "Elo serial touchscreens"
 	select SERIO

drivers/input/touchscreen/Makefile

@@ -31,6 +31,7 @@ obj-$(CONFIG_TOUCHSCREEN_EDT_FT5X06)	+= edt-ft5x06.o
 obj-$(CONFIG_TOUCHSCREEN_HAMPSHIRE)	+= hampshire.o
 obj-$(CONFIG_TOUCHSCREEN_GUNZE)		+= gunze.o
 obj-$(CONFIG_TOUCHSCREEN_EETI)		+= eeti_ts.o
+obj-$(CONFIG_TOUCHSCREEN_ELAN)		+= elants_i2c.o
 obj-$(CONFIG_TOUCHSCREEN_ELO)		+= elo.o
 obj-$(CONFIG_TOUCHSCREEN_EGALAX)	+= egalax_ts.o
 obj-$(CONFIG_TOUCHSCREEN_FUJITSU)	+= fujitsu_ts.o