[PATCH] psmouse: add support for 4th button using the 4th bit

[Aristeu Rozanski <arozansk@redhat.com>]

Cortron PS/2 Trackballs (700-0001A) reports the 4th button using the 4th
bit of the first packet (yes, it breaks the protocol). This patch adds
an extra protocol to generate BTN_SIDE based on the 4th bit. There's no
way to detect those trackballs using any kind of special sequence, thus
the protocol is only available if selected writing 'protocol' file in
sysfs, e.g.:
	echo -n "cortps" >/sys/devices/platform/i8042/serio1/protocol

Signed-off-by: Aristeu Rozanski <arozansk@redhat.com>

--- linus-2.6.orig/drivers/input/mouse/psmouse-base.c
+++ linus-2.6/drivers/input/mouse/psmouse-base.c
@@ -177,6 +177,15 @@ static psmouse_ret_t psmouse_process_byt
 	}
 
 /*
+ * Cortron PS2 Trackball reports SIDE button on the 4th bit of the first
+ * byte.
+ */
+	if (psmouse->type == PSMOUSE_CORTRON) {
+		input_report_key(dev, BTN_SIDE, (packet[0] >> 3) & 1);
+		packet[0] |= 0x08;
+	}
+
+/*
  * Generic PS/2 Mouse
  */
 
@@ -538,6 +547,20 @@ static int ps2bare_detect(struct psmouse
 	return 0;
 }
 
+/*
+ * Cortron PS/2 protocol detection. There's no special way to detect it, so it
+ * must be forced by sysfs protocol writing.
+ */
+static int cortron_detect(struct psmouse *psmouse, int set_properties)
+{
+	if (set_properties) {
+		psmouse->vendor = "Cortron";
+		psmouse->name = "PS/2 Trackball";
+		set_bit(BTN_SIDE, psmouse->dev->keybit);
+	}
+
+	return 0;
+}
 
 /*
  * psmouse_extensions() probes for any extensions to the basic PS/2 protocol
@@ -655,6 +678,12 @@ static const struct psmouse_protocol psm
 		.detect		= ps2bare_detect,
 	},
 	{
+		.type		= PSMOUSE_CORTRON,
+		.name		= "CortronPS/2",
+		.alias		= "cortps",
+		.detect		= cortron_detect,
+	},
+	{
 		.type		= PSMOUSE_PS2PP,
 		.name		= "PS2++",
 		.alias		= "logitech",
--- linus-2.6.orig/drivers/input/mouse/psmouse.h
+++ linus-2.6/drivers/input/mouse/psmouse.h
@@ -78,6 +78,7 @@ struct psmouse {
 enum psmouse_type {
 	PSMOUSE_NONE,
 	PSMOUSE_PS2,
+	PSMOUSE_CORTRON,
 	PSMOUSE_PS2PP,
 	PSMOUSE_THINKPS,
 	PSMOUSE_GENPS,