[PATCH] input: elantech.c provide a workaround for jumpy cursor on firmware 2.34

[Arjan Opmeer <arjan@opmeer.net>]

From: Arjan Opmeer <arjan@opmeer.net>

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, enabled by default for firmware
version 2.34, that discards mouse packets that are likely to contain bogus
coordinates. To allow users of other firmware versions, that may also see
this problem, to experiment the workaround can be enabled and disabled via a
sysfs entry.

Signed-off-by: Arjan Opmeer <arjan@opmeer.net>
---

diff --git a/Documentation/input/elantech.txt b/Documentation/input/elantech.txt
index a10c3b6..3156a8e 100644
--- a/Documentation/input/elantech.txt
+++ b/Documentation/input/elantech.txt
@@ -1,7 +1,7 @@
 Elantech Touchpad Driver
 ========================
 
-	Copyright (C) 2007-2008 Arjan Opmeer <arjan@opmeer.net>
+	Copyright (C) 2007-2009 Arjan Opmeer <arjan@opmeer.net>
 
 	Extra information for hardware version 1 found and
 	provided by Steve Havelka
@@ -64,8 +64,8 @@ completeness sake.
 2. Extra knobs
    ~~~~~~~~~~~
 
-Currently the Linux Elantech touchpad driver provides two extra knobs under
-/sys/bus/serio/drivers/psmouse/serio? for the user.
+Currently the Linux Elantech touchpad driver provides three extra knobs
+under /sys/bus/serio/drivers/psmouse/serio? for the user.
 
 * debug
 
@@ -98,6 +98,20 @@ Currently the Linux Elantech touchpad driver provides two extra knobs under
    bits. Hence checking is disabled by default. Currently even turning it on
    will do nothing.
 
+* jumpy_cursor
+
+   Turns a workaround for jumpy mouse cursor ON or OFF.
+
+   By echo "0" to to this file the workaround will be turned OFF. Any
+   non-zero value will turn it ON. For firmware version 2.34 the default is
+   ON.
+
+   Firmware version 2.34 seems to suffer from a problem where in the
+   starting phase of a touch action bogus coordinates are reported. This
+   causes the mouse cursor or the scrolled page to jump. This knob enables a
+   workaround that discards mouse packets likely to contain bogus
+   coordinates.
+
 
 /////////////////////////////////////////////////////////////////////////////
 
diff --git a/drivers/input/mouse/elantech.c b/drivers/input/mouse/elantech.c
index 6ab0eb1..da3ff23 100644
--- a/drivers/input/mouse/elantech.c
+++ b/drivers/input/mouse/elantech.c
@@ -1,7 +1,7 @@
 /*
- * 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;
 }
 
 /*
@@ -507,6 +519,7 @@ ELANTECH_INT_ATTR(reg_25, 0x25);
 ELANTECH_INT_ATTR(reg_26, 0x26);
 ELANTECH_INT_ATTR(debug, 0);
 ELANTECH_INT_ATTR(paritycheck, 0);
+ELANTECH_INT_ATTR(jumpy_cursor, 0);
 
 static struct attribute *elantech_attrs[] = {
 	&psmouse_attr_reg_10.dattr.attr,
@@ -520,6 +533,7 @@ static struct attribute *elantech_attrs[] = {
 	&psmouse_attr_reg_26.dattr.attr,
 	&psmouse_attr_debug.dattr.attr,
 	&psmouse_attr_paritycheck.dattr.attr,
+	&psmouse_attr_jumpy_cursor.dattr.attr,
 	NULL
 };
 
@@ -662,6 +676,17 @@ 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;
diff --git a/drivers/input/mouse/elantech.h b/drivers/input/mouse/elantech.h
index bee282b..ed848cc 100644
--- a/drivers/input/mouse/elantech.h
+++ b/drivers/input/mouse/elantech.h
@@ -1,7 +1,7 @@
 /*
- * 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];
 };