Input: ad7879 - allow exporting AUX/VBAT/GPIO pin via device property

Up until now only platforms using legacy platform data were able to switch
AUX/VBAT/GPIO pin in GPIO mode and use it as regular GPIO line. Let's
allow platforms using generic device properties to do the same.
Reviewed-by: NMichael Hennerich <michael.hennerich@analog.com>
Tested-by: NMichael Hennerich <michael.hennerich@analog.com>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/ad7879.txt

@@ -35,6 +35,7 @@ Optional properties:
 - adi,conversion-interval:	: 0    : convert one time only
 				  1-255: 515us + val * 35us (up to 9.440ms)
 				  This property has to be a '/bits/ 8' value
+- gpio-controller		: Switch AUX/VBAT/GPIO pin to GPIO mode
 
 Example:
 

drivers/input/touchscreen/ad7879.c

@@ -454,17 +454,28 @@ static void ad7879_gpio_set_value(struct gpio_chip *chip,
 static int ad7879_gpio_add(struct ad7879 *ts,
 			   const struct ad7879_platform_data *pdata)
 {
+	bool gpio_export;
+	int gpio_base;
 	int ret = 0;
 
+	if (pdata) {
+		gpio_export = pdata->gpio_export;
+		gpio_base = pdata->gpio_base;
+	} else {
+		gpio_export = device_property_read_bool(ts->dev,
+							"gpio-controller");
+		gpio_base = -1;
+	}
+
 	mutex_init(&ts->mutex);
 
-	if (pdata && pdata->gpio_export) {
+	if (gpio_export) {
 		ts->gc.direction_input = ad7879_gpio_direction_input;
 		ts->gc.direction_output = ad7879_gpio_direction_output;
 		ts->gc.get = ad7879_gpio_get_value;
 		ts->gc.set = ad7879_gpio_set_value;
 		ts->gc.can_sleep = 1;
-		ts->gc.base = pdata->gpio_base;
+		ts->gc.base = gpio_base;
 		ts->gc.ngpio = 1;
 		ts->gc.label = "AD7879-GPIO";
 		ts->gc.owner = THIS_MODULE;