Input: sentelic - filter out erratic movement when lifting finger

When lifing finger off the surface some versions of touchpad send movement
packets with very low coordinates, which cause cursor to jump to the upper
left corner of the screen. Let's ignore least significant bits of X and Y
coordinates if higher bits are all zeroes and consider finger not touching
the pad.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=43197
Reported-and-tested-by:	Aleksey Spiridonov <leks13@leks13.ru>
Tested-by: Eddie Dunn <eddie.dunn@gmail.com>
Tested-by: Jakub Luzny <limoto94@gmail.com>
Tested-by: Olivier Goffart <olivier@woboq.com>
Signed-off-by: Tai-hwa Liang <avatar@sentelic.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/mouse/sentelic.c

@@ -721,6 +721,17 @@ static psmouse_ret_t fsp_process_byte(struct psmouse *psmouse)
 
 	switch (psmouse->packet[0] >> FSP_PKT_TYPE_SHIFT) {
 	case FSP_PKT_TYPE_ABS:
+
+		if ((packet[0] == 0x48 || packet[0] == 0x49) &&
+		    packet[1] == 0 && packet[2] == 0) {
+			/*
+			 * Ignore coordinate noise when finger leaving the
+			 * surface, otherwise cursor may jump to upper-left
+			 * corner.
+			 */
+			packet[3] &= 0xf0;
+		}
+
 		abs_x = GET_ABS_X(packet);
 		abs_y = GET_ABS_Y(packet);