differentiate anymore when they dis-align. And I don't think using motion
will help because the hardware tends to report _exactly_ the same value
as soon the two fingers become close (= a segment instead of a
rectangle).  Or motion tracking would require a long window of past
frames.

I still think that for the very specific use case of scrolling when
pressing one finger and moving up and dow the other one, reporting the
average works better than the first finger. However, I guess this can be
considered just as a drawback of the ST protocol, and fixed in userspace
by using the MT protocol.

What do you think? Does it look fine to you? Below is the code.

Eric


8<--------------------------------------------------------------------
The elantech hardware is limited when reporting two fingers. It just
reports the minimum and maximum coordinates of the rectangle containing
the fingers.

As multitouch protocol requires at least to report the correct position
of each finger, we track the finger position when there is only one
finger to distinguish which corner of the rectangle corresponds to the
actual position of the fingers. When there are three fingers, only the
minimum position is reported, so we just don't track it and hope the
last tracked position has the most likelihood to be correct.

It works fine, at least as long as the two fingers don't get
horizontally or vertically aligned, after what it's back to random.
This also allows to avoid so "jumps" in the single-touch protocol.

Signed-off-by: Éric Piel <eric.piel@tremplin-utc.net>
---
 drivers/input/mouse/elantech.c |   51 ++++++++++++++++++++++++++++++++--------
 drivers/input/mouse/elantech.h |    2 +
 2 files changed, 43 insertions(+), 10 deletions(-)

diff --git a/drivers/input/mouse/elantech.c b/drivers/input/mouse/elantech.c
index bb66ae8..a3a3d8d 100644
--- a/drivers/input/mouse/elantech.c
+++ b/drivers/input/mouse/elantech.c
@@ -242,6 +242,33 @@ static void elantech_report_absolute_v1(struct psmouse *psmouse)
 	input_sync(dev);
 }
 
+
+static void track_one_finger(struct elantech_data *etd, int x, int y)
+{
+	etd->prev_x = x;
+	etd->prev_y = y;
+}
+
+static void find_closest_and_swap(int *ref, int *a, int *b)
+{
+	int diff_a = abs(*ref - *a);
+	int diff_b = abs(*ref - *b);
+	int tmp;
+	if (diff_b < diff_a) {
+		tmp = *a;
+		*a = *b;
+		*b = tmp;
+	}
+	*ref = *a;
+}
+
+static void track_two_fingers(struct elantech_data *etd, int *x1, int *y1, int *x2, int *y2)
+{
+	find_closest_and_swap(&etd->prev_x, x1, x2);
+	find_closest_and_swap(&etd->prev_y, y1, y2);
+}
+
+
 /*
  * Interpret complete data packets and report absolute mode input events for
  * hardware version 2. (6 byte packets)
@@ -284,6 +311,8 @@ static void elantech_report_absolute_v2(struct psmouse *psmouse)
 
 		input_report_abs(dev, ABS_X, x1);
 		input_report_abs(dev, ABS_Y, y1);
+		if (fingers == 1)
+			track_one_finger(etd, x1, y1);
 
 		pres = (packet[1] & 0xf0) | ((packet[4] & 0xf0) >> 4);
 		width = ((packet[0] & 0x30) >> 2) | ((packet[3] & 0x30) >> 4);
@@ -296,29 +325,31 @@ static void elantech_report_absolute_v2(struct psmouse *psmouse)
 		 * byte 0:  .   .  ay8 ax8  .   .   .   .
 		 * byte 1: ax7 ax6 ax5 ax4 ax3 ax2 ax1 ax0
 		 */
-		x1 = ((packet[0] & 0x10) << 4) | packet[1];
+		x1 = (((packet[0] & 0x10) << 4) | packet[1]) << 2;
 		/* byte 2: ay7 ay6 ay5 ay4 ay3 ay2 ay1 ay0 */
-		y1 = ETP_2FT_YMAX - (((packet[0] & 0x20) << 3) | packet[2]);
+		y1 = (ETP_2FT_YMAX - (((packet[0] & 0x20) << 3) | packet[2])) << 2;
 		/*
 		 * byte 3:  .   .  by8 bx8  .   .   .   .
 		 * byte 4: bx7 bx6 bx5 bx4 bx3 bx2 bx1 bx0
 		 */
-		x2 = ((packet[3] & 0x10) << 4) | packet[4];
+		x2 = (((packet[3] & 0x10) << 4) | packet[4]) << 2;
 		/* byte 5: by7 by8 by5 by4 by3 by2 by1 by0 */
-		y2 = ETP_2FT_YMAX - (((packet[3] & 0x20) << 3) | packet[5]);
+		y2 = (ETP_2FT_YMAX - (((packet[3] & 0x20) << 3) | packet[5])) << 2;
+
+		track_two_fingers(etd, &x1, &y1, &x2, &y2);
 		/* Multitouch */
-		input_report_abs(dev, ABS_MT_POSITION_X, x1 << 2);
-		input_report_abs(dev, ABS_MT_POSITION_Y, y1 << 2);
+		input_report_abs(dev, ABS_MT_POSITION_X, x1);
+		input_report_abs(dev, ABS_MT_POSITION_Y, y1);
 		input_mt_sync(dev);
-		input_report_abs(dev, ABS_MT_POSITION_X, x2 << 2);
-		input_report_abs(dev, ABS_MT_POSITION_Y, y2 << 2);
+		input_report_abs(dev, ABS_MT_POSITION_X, x2);
+		input_report_abs(dev, ABS_MT_POSITION_Y, y2);
 		input_mt_sync(dev);
 		/*
 		 * For compatibility with non-multitouch userspace apps
 		 * report the average of both coordinates and scale up.
 		 */
-		input_report_abs(dev, ABS_X, (x1 + x2) << 1);
-		input_report_abs(dev, ABS_Y, (y1 + y2) << 1);
+		input_report_abs(dev, ABS_X, (x1 + x2) >> 1);
+		input_report_abs(dev, ABS_Y, (y1 + y2) >> 1);
 		/*
 		 * For compatibility with the proprietary X Elantech driver
 		 * report both coordinates as hat coordinates
diff --git a/drivers/input/mouse/elantech.h b/drivers/input/mouse/elantech.h
index f6e3be5..fa9a6b4 100644
--- a/drivers/input/mouse/elantech.h
+++ b/drivers/input/mouse/elantech.h
@@ -111,6 +111,8 @@ struct elantech_data {
 	unsigned char hw_version;
 	unsigned int  fw_version;
 	unsigned char parity[256];
+	unsigned int prev_x;
+	unsigned int prev_y;
 };
 
 enum paritycheck_types {
