[PATCH v2] Input: goodix: Add support for capacitive home button found on some x86 tablets

["Sergei A. Trusov" <sergei.a.trusov@ya.ru>]

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 normally only the lower 4 bits
are used to indicate the number of touches.

Detect this and report a KEY_LEFTMETA press when this happens. Note the
hardware might support more than one button, the number of a button is
reported by the 'id' byte of coor_data. Now we ignore button id.

Signed-off-by: Sergei A. Trusov <sergei.a.trusov@ya.ru>
---
 drivers/input/touchscreen/goodix.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/input/touchscreen/goodix.c b/drivers/input/touchscreen/goodix.c
index 240b16f3ee97..c1bb59c96dbd 100644
--- a/drivers/input/touchscreen/goodix.c
+++ b/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] & 0x10));
+
 	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,