Input: synaptics - use in-kernel tracking for reporting mt data

The current code tries to consider all states and transitions to properly
detect which finger is attached to which slot. The code is quite huge
and difficult to read.

If the sensor manages to group the touch points but is not reliable in
giving tracking ids, we can simply use the kernel tracking method. Note
that it is already used by Cr-48 Chromebooks.

Incidentaly, this fixes a bug reported by Peter Hutterer:
"""
on the Lenovo T440, run:
evemu-record /dev/input/event4 | grep BTN_

then put one, two, three, two fingers down
when you go from 3 to 2 fingers the driver sends a spurious BTN_TOUCH 0
event:

E: 0.000000 0001 014a 0001      # EV_KEY / BTN_TOUCH            1
E: 0.000000 0001 0145 0001      # EV_KEY / BTN_TOOL_FINGER      1
E: 0.770008 0001 0145 0000      # EV_KEY / BTN_TOOL_FINGER      0
E: 0.770008 0001 014d 0001      # EV_KEY / BTN_TOOL_DOUBLETAP   1
E: 1.924716 0001 014d 0000      # EV_KEY / BTN_TOOL_DOUBLETAP   0
E: 1.924716 0001 014e 0001      # EV_KEY / BTN_TOOL_TRIPLETAP   1

.. changing from 3 to 2 fingers now

E: 3.152641 0001 014a 0000      # EV_KEY / BTN_TOUCH            0
E: 3.152641 0001 014d 0001      # EV_KEY / BTN_TOOL_DOUBLETAP   1
E: 3.152641 0001 014e 0000      # EV_KEY / BTN_TOOL_TRIPLETAP   0
E: 3.176948 0001 014a 0001      # EV_KEY / BTN_TOUCH            1

quick look in the kernel shows it's caused by hw.z going to 0 for a packet,
so probably a firmware bug. either way, it makes it hard to track BTN_TOUCH
as signal that at least one finger is down.
"""

The in-kernel tracking is enough to remove this spurious BTN_TOUCH 0.
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/synaptics.h

@@ -118,16 +118,6 @@
 /* amount to fuzz position data when touchpad reports reduced filtering */
 #define SYN_REDUCED_FILTER_FUZZ		8
 
-/*
- * A structure to describe which internal touchpad finger slots are being
- * reported in raw packets.
- */
-struct synaptics_mt_state {
-	int count;			/* num fingers being tracked */
-	int sgm;			/* which slot is reported by sgm pkt */
-	int agm;			/* which slot is reported by agm pkt*/
-};
-
 /*
  * A structure to describe the state of the touchpad hardware (buttons and pad)
  */
@@ -143,9 +133,6 @@ struct synaptics_hw_state {
 	unsigned int down:1;
 	unsigned char ext_buttons;
 	signed char scroll;
-
-	/* As reported in last AGM-CONTACT packets */
-	struct synaptics_mt_state mt_state;
 };
 
 struct synaptics_data {
@@ -170,15 +157,12 @@ struct synaptics_data {
 
 	struct serio *pt_port;			/* Pass-through serio port */
 
-	struct synaptics_mt_state mt_state;	/* Current mt finger state */
-	bool mt_state_lost;			/* mt_state may be incorrect */
-
 	/*
 	 * Last received Advanced Gesture Mode (AGM) packet. An AGM packet
 	 * contains position data for a second contact, at half resolution.
 	 */
 	struct synaptics_hw_state agm;
-	bool agm_pending;			/* new AGM packet received */
+	unsigned int agm_count;			/* finger count reported by agm */
 
 	/* ForcePad handling */
 	unsigned long				press_start;