[PATCH] 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 0th 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 | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/input/touchscreen/goodix.c b/drivers/input/touchscreen/goodix.c
index 240b16f3ee97..a4c17c461792 100644
--- a/drivers/input/touchscreen/goodix.c
+++ b/drivers/input/touchscreen/goodix.c
@@ -76,6 +76,10 @@ struct goodix_ts_data {
 #define MAX_CONTACTS_LOC	5
 #define TRIGGER_LOC		6
 
+#define GOODIX_TOUCH_NUM_MASK		0x0f
+#define GOODIX_SOFTBUTTON_MASK		0x10
+#define GOODIX_SOFTBUTTON1		KEY_LEFTMETA
+
 static const unsigned long goodix_irq_flags[] = {
 	IRQ_TYPE_EDGE_RISING,
 	IRQ_TYPE_EDGE_FALLING,
@@ -208,7 +212,7 @@ static int goodix_ts_read_input_report(struct goodix_ts_data *ts, u8 *data)
 	if (!(data[0] & 0x80))
 		return -EAGAIN;
 
-	touch_num = data[0] & 0x0f;
+	touch_num = data[0] & GOODIX_TOUCH_NUM_MASK;
 	if (touch_num > ts->max_touch_num)
 		return -EPROTO;
 
@@ -223,7 +227,7 @@ static int goodix_ts_read_input_report(struct goodix_ts_data *ts, u8 *data)
 			return error;
 	}
 
-	return touch_num;
+	return data[0];
 }
 
 static void goodix_ts_report_touch(struct goodix_ts_data *ts, u8 *coor_data)
@@ -260,13 +264,17 @@ static void goodix_ts_report_touch(struct goodix_ts_data *ts, u8 *coor_data)
 static void goodix_process_events(struct goodix_ts_data *ts)
 {
 	u8  point_data[1 + GOODIX_CONTACT_SIZE * GOODIX_MAX_CONTACTS];
-	int touch_num;
+	int touch_num, status;
 	int i;
 
-	touch_num = goodix_ts_read_input_report(ts, point_data);
-	if (touch_num < 0)
+	status = goodix_ts_read_input_report(ts, point_data);
+	if (status < 0)
 		return;
 
+	input_report_key(ts->input_dev, GOODIX_SOFTBUTTON1,
+			!!(status & GOODIX_SOFTBUTTON_MASK));
+
+	touch_num = status & GOODIX_TOUCH_NUM_MASK;
 	for (i = 0; i < touch_num; i++)
 		goodix_ts_report_touch(ts,
 				&point_data[1 + GOODIX_CONTACT_SIZE * i]);
@@ -612,6 +620,8 @@ 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;
 
+	input_set_capability(ts->input_dev, EV_KEY, GOODIX_SOFTBUTTON1);
+
 	error = input_register_device(ts->input_dev);
 	if (error) {
 		dev_err(&ts->client->dev,