Input: appletouch - fix jumps when additional fingers are detected

Addresses issues related to when a second finger enters or leaves the
field, causing the cursor to jump or the page to scroll unexpectedly; now,
we discard any movement change that happens at the exact moment we detect a
change in the number of fingers touching the trackpad. This doesn't
completely resolve the issue but does greatly mitigate it.

Signed-off-by: Clinton Sprain <clintonsprain@gmail.com>
Reviewed-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/appletouch.c

@@ -218,6 +218,7 @@ struct atp {
 	bool			valid;		/* are the samples valid? */
 	bool			size_detect_done;
 	bool			overflow_warned;
+	int			fingers_old;	/* last reported finger count */
 	int			x_old;		/* last reported x/y, */
 	int			y_old;		/* used for smoothing */
 	signed char		xy_cur[ATP_XSENSORS + ATP_YSENSORS];
@@ -528,7 +529,7 @@ static void atp_complete_geyser_1_2(struct urb *urb)
 {
 	int x, y, x_z, y_z, x_f, y_f;
 	int retval, i, j;
-	int key;
+	int key, fingers;
 	struct atp *dev = urb->context;
 	int status = atp_status_check(urb);
 
@@ -611,7 +612,9 @@ static void atp_complete_geyser_1_2(struct urb *urb)
 			      dev->info->yfact, &y_z, &y_f);
 	key = dev->data[dev->info->datalen - 1] & ATP_STATUS_BUTTON;
 
-	if (x && y) {
+	fingers = max(x_f, y_f);
+
+	if (x && y && fingers == dev->fingers_old) {
 		if (dev->x_old != -1) {
 			x = (dev->x_old * 7 + x) >> 3;
 			y = (dev->y_old * 7 + y) >> 3;
@@ -628,14 +631,15 @@ static void atp_complete_geyser_1_2(struct urb *urb)
 			input_report_abs(dev->input, ABS_Y, y);
 			input_report_abs(dev->input, ABS_PRESSURE,
 					 min(ATP_PRESSURE, x_z + y_z));
-			atp_report_fingers(dev->input, max(x_f, y_f));
+			atp_report_fingers(dev->input, fingers);
 		}
 		dev->x_old = x;
 		dev->y_old = y;
 
 	} else if (!x && !y) {
 
 		dev->x_old = dev->y_old = -1;
+		dev->fingers_old = 0;
 		input_report_key(dev->input, BTN_TOUCH, 0);
 		input_report_abs(dev->input, ABS_PRESSURE, 0);
 		atp_report_fingers(dev->input, 0);
@@ -644,6 +648,10 @@ static void atp_complete_geyser_1_2(struct urb *urb)
 		memset(dev->xy_acc, 0, sizeof(dev->xy_acc));
 	}
 
+	if (fingers != dev->fingers_old)
+		dev->x_old = dev->y_old = -1;
+	dev->fingers_old = fingers;
+
 	input_report_key(dev->input, BTN_LEFT, key);
 	input_sync(dev->input);
 
@@ -661,7 +669,7 @@ static void atp_complete_geyser_3_4(struct urb *urb)
 {
 	int x, y, x_z, y_z, x_f, y_f;
 	int retval, i, j;
-	int key;
+	int key, fingers;
 	struct atp *dev = urb->context;
 	int status = atp_status_check(urb);
 
@@ -724,7 +732,9 @@ static void atp_complete_geyser_3_4(struct urb *urb)
 
 	key = dev->data[dev->info->datalen - 1] & ATP_STATUS_BUTTON;
 
-	if (x && y) {
+	fingers = max(x_f, y_f);
+
+	if (x && y && fingers == dev->fingers_old) {
 		if (dev->x_old != -1) {
 			x = (dev->x_old * 7 + x) >> 3;
 			y = (dev->y_old * 7 + y) >> 3;
@@ -741,14 +751,15 @@ static void atp_complete_geyser_3_4(struct urb *urb)
 			input_report_abs(dev->input, ABS_Y, y);
 			input_report_abs(dev->input, ABS_PRESSURE,
 					 min(ATP_PRESSURE, x_z + y_z));
-			atp_report_fingers(dev->input, max(x_f, y_f));
+			atp_report_fingers(dev->input, fingers);
 		}
 		dev->x_old = x;
 		dev->y_old = y;
 
 	} else if (!x && !y) {
 
 		dev->x_old = dev->y_old = -1;
+		dev->fingers_old = 0;
 		input_report_key(dev->input, BTN_TOUCH, 0);
 		input_report_abs(dev->input, ABS_PRESSURE, 0);
 		atp_report_fingers(dev->input, 0);
@@ -757,6 +768,10 @@ static void atp_complete_geyser_3_4(struct urb *urb)
 		memset(dev->xy_acc, 0, sizeof(dev->xy_acc));
 	}
 
+	if (fingers != dev->fingers_old)
+		dev->x_old = dev->y_old = -1;
+	dev->fingers_old = fingers;
+
 	input_report_key(dev->input, BTN_LEFT, key);
 	input_sync(dev->input);