Input: goodix - add support for capacitive home button

On some x86 tablets with a Goodix touchscreen, the Windows logo on the
front is a capacitive home button. Touching this button results in a touch
with bit 4 of the first byte set, while only the lower 4 bits (0-3) are
used to indicate the number of touches.

Report a KEY_LEFTMETA press when this happens.

Note that the hardware might support more than one button, in which
case the "id" byte of coor_data would identify the button in question.
This is not implemented as we don't have access to hardware with
multiple buttons.

Signed-off-by: Sergei A. Trusov <sergei.a.trusov@ya.ru>
Acked-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/goodix.c

@@ -267,6 +267,12 @@ static void goodix_process_events(struct goodix_ts_data *ts)
 	if (touch_num < 0)
 		return;
 
+	/*
+	 * Bit 4 of the first byte reports the status of the capacitive
+	 * Windows/Home button.
+	 */
+	input_report_key(ts->input_dev, KEY_LEFTMETA, point_data[0] & BIT(4));
+
 	for (i = 0; i < touch_num; i++)
 		goodix_ts_report_touch(ts,
 				&point_data[1 + GOODIX_CONTACT_SIZE * i]);
@@ -612,6 +618,9 @@ static int goodix_request_input_dev(struct goodix_ts_data *ts)
 	ts->input_dev->id.product = ts->id;
 	ts->input_dev->id.version = ts->version;
 
+	/* Capacitive Windows/Home button on some devices */
+	input_set_capability(ts->input_dev, EV_KEY, KEY_LEFTMETA);
+
 	error = input_register_device(ts->input_dev);
 	if (error) {
 		dev_err(&ts->client->dev,