Input: elantech - provide a workaround for jumpy cursor on firmware 2.34

It seems that Elantech touchpad firmware version 2.34 on the Hercules eCAFÉ
suffers from a problem where bogus coordinates get reported at the beginning
of a touch action. This causes the mouse cursor or the scrolled page to
jump.

Included patch provides a workaround that discards mouse packets that are
likely to contain bogus coordinates. The workaround is activated when we
detect touchpad with fimware version 2.34.
Signed-off-by: Arjan Opmeer <arjan@opmeer.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/mouse/elantech.c

 /*
- * Elantech Touchpad driver (v5)
+ * Elantech Touchpad driver (v6)
  *
- * Copyright (C) 2007-2008 Arjan Opmeer <arjan@opmeer.net>
+ * Copyright (C) 2007-2009 Arjan Opmeer <arjan@opmeer.net>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 as published
@@ -178,6 +178,7 @@ static void elantech_report_absolute_v1(struct psmouse *psmouse)
 	struct elantech_data *etd = psmouse->private;
 	unsigned char *packet = psmouse->packet;
 	int fingers;
+	static int old_fingers;
 
 	if (etd->fw_version_maj == 0x01) {
 		/* byte 0:  D   U  p1  p2   1  p3   R   L
@@ -190,6 +191,14 @@ static void elantech_report_absolute_v1(struct psmouse *psmouse)
 		fingers = (packet[0] & 0xc0) >> 6;
 	}
 
+	if (etd->jumpy_cursor) {
+		/* Discard packets that are likely to have bogus coordinates */
+		if (fingers > old_fingers) {
+			elantech_debug("elantech.c: discarding packet\n");
+			goto discard_packet_v1;
+		}
+	}
+
 	input_report_key(dev, BTN_TOUCH, fingers != 0);
 
 	/* byte 2: x7  x6  x5  x4  x3  x2  x1  x0
@@ -216,6 +225,9 @@ static void elantech_report_absolute_v1(struct psmouse *psmouse)
 	}
 
 	input_sync(dev);
+
+ discard_packet_v1:
+	old_fingers = fingers;
 }
 
 /*
@@ -662,6 +674,17 @@ int elantech_init(struct psmouse *psmouse)
 		param[0], param[1], param[2]);
 	etd->capabilities = param[0];
 
+	/*
+	 * This firmware seems to suffer from misreporting coordinates when
+	 * a touch action starts causing the mouse cursor or scrolled page
+	 * to jump. Enable a workaround.
+	 */
+	if (etd->fw_version_maj == 0x02 && etd->fw_version_min == 0x22) {
+		pr_info("elantech.c: firmware version 2.34 detected, "
+			"enabling jumpy cursor workaround\n");
+		etd->jumpy_cursor = 1;
+	}
+
 	if (elantech_set_absolute_mode(psmouse)) {
 		pr_err("elantech.c: failed to put touchpad into absolute mode.\n");
 		goto init_fail;

drivers/input/mouse/elantech.h

 /*
- * Elantech Touchpad driver (v5)
+ * Elantech Touchpad driver (v6)
  *
- * Copyright (C) 2007-2008 Arjan Opmeer <arjan@opmeer.net>
+ * Copyright (C) 2007-2009 Arjan Opmeer <arjan@opmeer.net>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 as published
@@ -104,6 +104,7 @@ struct elantech_data {
 	unsigned char fw_version_min;
 	unsigned char hw_version;
 	unsigned char paritycheck;
+	unsigned char jumpy_cursor;
 	unsigned char parity[256];
 };