Input: elantech - report multitouch with proper ABS_MT messages

Multitouch info was reported only via a old protocol used by the
proprietary X driver from elantech. Let's report the multitouch info
also following the official MT protocol. It's semi-mt because the device
only reports the lowest/highest coordinates.

This was done following the multi-touch-protocol.txt documentation, and
inspired by the bcm5974 and elantech implementations. Testing was light
as there is not many applications using this protocol yet, but the X
synaptics driver didn't complain and the X multitouch driver behaved
correctly.

Signed-off-by: Éric Piel <eric.piel@tremplin-utc.net>
Reviewed-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/mouse/elantech.c

@@ -16,6 +16,7 @@
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/input.h>
+#include <linux/input/mt.h>
 #include <linux/serio.h>
 #include <linux/libps2.h>
 #include "psmouse.h"
@@ -242,6 +243,27 @@ static void elantech_report_absolute_v1(struct psmouse *psmouse)
 	input_sync(dev);
 }
 
+static void elantech_set_slot(struct input_dev *dev, int slot, bool active,
+			      unsigned int x, unsigned int y)
+{
+	input_mt_slot(dev, slot);
+	input_mt_report_slot_state(dev, MT_TOOL_FINGER, active);
+	if (active) {
+		input_report_abs(dev, ABS_MT_POSITION_X, x);
+		input_report_abs(dev, ABS_MT_POSITION_Y, y);
+	}
+}
+
+/* x1 < x2 and y1 < y2 when two fingers, x = y = 0 when not pressed */
+static void elantech_report_semi_mt_data(struct input_dev *dev,
+					 unsigned int num_fingers,
+					 unsigned int x1, unsigned int y1,
+					 unsigned int x2, unsigned int y2)
+{
+	elantech_set_slot(dev, 0, num_fingers != 0, x1, y1);
+	elantech_set_slot(dev, 1, num_fingers == 2, x2, y2);
+}
+
 /*
  * Interpret complete data packets and report absolute mode input events for
  * hardware version 2. (6 byte packets)
@@ -251,7 +273,7 @@ static void elantech_report_absolute_v2(struct psmouse *psmouse)
 	struct elantech_data *etd = psmouse->private;
 	struct input_dev *dev = psmouse->dev;
 	unsigned char *packet = psmouse->packet;
-	int fingers, x1, y1, x2, y2, width = 0, pres = 0;
+	unsigned int fingers, x1 = 0, y1 = 0, x2 = 0, y2 = 0, width = 0, pres = 0;
 
 	/* byte 0: n1  n0   .   .   .   .   R   L */
 	fingers = (packet[0] & 0xc0) >> 6;
@@ -271,14 +293,16 @@ static void elantech_report_absolute_v2(struct psmouse *psmouse)
 		 * byte 1:  .   .   .   .   .  x10 x9  x8
 		 * byte 2: x7  x6  x5  x4  x4  x2  x1  x0
 		 */
-		input_report_abs(dev, ABS_X,
-			((packet[1] & 0x07) << 8) | packet[2]);
+		x1 = ((packet[1] & 0x07) << 8) | packet[2];
 		/*
 		 * byte 4:  .   .   .   .   .   .  y9  y8
 		 * byte 5: y7  y6  y5  y4  y3  y2  y1  y0
 		 */
-		input_report_abs(dev, ABS_Y,
-			ETP_YMAX_V2 - (((packet[4] & 0x03) << 8) | packet[5]));
+		y1 = ETP_YMAX_V2 - (((packet[4] & 0x03) << 8) | packet[5]);
+
+		input_report_abs(dev, ABS_X, x1);
+		input_report_abs(dev, ABS_Y, y1);
+
 		pres = (packet[1] & 0xf0) | ((packet[4] & 0xf0) >> 4);
 		width = ((packet[0] & 0x30) >> 2) | ((packet[3] & 0x30) >> 4);
 		break;
@@ -321,6 +345,7 @@ static void elantech_report_absolute_v2(struct psmouse *psmouse)
 		break;
 	}
 
+	elantech_report_semi_mt_data(dev, fingers, x1, y1, x2, y2);
 	input_report_key(dev, BTN_TOOL_FINGER, fingers == 1);
 	input_report_key(dev, BTN_TOOL_DOUBLETAP, fingers == 2);
 	input_report_key(dev, BTN_TOOL_TRIPLETAP, fingers == 3);
@@ -495,6 +520,10 @@ static void elantech_set_input_params(struct psmouse *psmouse)
 			input_set_abs_params(dev, ABS_TOOL_WIDTH, ETP_WMIN_V2,
 					     ETP_WMAX_V2, 0, 0);
 		}
+		__set_bit(INPUT_PROP_SEMI_MT, dev->propbit);
+		input_mt_init_slots(dev, 2);
+		input_set_abs_params(dev, ABS_MT_POSITION_X, ETP_XMIN_V2, ETP_XMAX_V2, 0, 0);
+		input_set_abs_params(dev, ABS_MT_POSITION_Y, ETP_YMIN_V2, ETP_YMAX_V2, 0, 0);
 		input_set_abs_params(dev, ABS_HAT0X, ETP_2FT_XMIN, ETP_2FT_XMAX, 0, 0);
 		input_set_abs_params(dev, ABS_HAT0Y, ETP_2FT_YMIN, ETP_2FT_YMAX, 0, 0);
 		input_set_abs_params(dev, ABS_HAT1X, ETP_2FT_XMIN, ETP_2FT_XMAX, 0, 0);