Input: multitouch - add tracking ID to the protocol

There are a few multi-touch devices that support finger tracking
well in hardware, Stantum being the prime example. By exposing the
tracking ID in the MT protocol, evdev bandwidth and cpu usage in
user space can be reduced.

This patch adds the ABS_MT_TRACKING_ID to the MT protocol.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Tested-by: Stéphane Chatty <chatty@enac.fr>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/input.c

@@ -42,6 +42,7 @@ static unsigned int input_abs_bypass_init_data[] __initdata = {
 	ABS_MT_POSITION_Y,
 	ABS_MT_TOOL_TYPE,
 	ABS_MT_BLOB_ID,
+	ABS_MT_TRACKING_ID,
 	0
 };
 static unsigned long input_abs_bypass[BITS_TO_LONGS(ABS_CNT)];

include/linux/input.h

@@ -656,6 +656,7 @@ struct input_absinfo {
 #define ABS_MT_POSITION_Y	0x36	/* Center Y ellipse position */
 #define ABS_MT_TOOL_TYPE	0x37	/* Type of touching device */
 #define ABS_MT_BLOB_ID		0x38	/* Group a set of packets as a blob */
+#define ABS_MT_TRACKING_ID	0x39	/* Unique ID of initiated contact */
 
 #define ABS_MAX			0x3f
 #define ABS_CNT			(ABS_MAX+1)