input: keychord: Add keychord driver

This driver allows userspace to receive notification when client
specified key combinations are pressed.
The client opens /dev/keychord and writes a list of keychords
for the driver to monitor.
The client then reads or polls /dev/keychord for notifications.
A client specified ID for the keychord is returned from read()
when a keychord press is detected.

Signed-off-by: Mike Lockwood <lockwood@android.com>

keychord: fix to build without CONFIG_PREEMPT

Change-Id: I911f13aeda4224b6fa57863bc7e8972fec8837fb

include/linux/keychord.h

@@ -0,0 +1,52 @@
+/*
+ *  Key chord input driver
+ *
+ * Copyright (C) 2008 Google, Inc.
+ * Author: Mike Lockwood <lockwood@android.com>
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+*/
+
+#ifndef __LINUX_KEYCHORD_H_
+#define __LINUX_KEYCHORD_H_
+
+#include <linux/input.h>
+
+#define KEYCHORD_VERSION		1
+
+/*
+ * One or more input_keychord structs are written to /dev/keychord
+ * at once to specify the list of keychords to monitor.
+ * Reading /dev/keychord returns the id of a keychord when the
+ * keychord combination is pressed.  A keychord is signalled when
+ * all of the keys in the keycode list are in the pressed state.
+ * The order in which the keys are pressed does not matter.
+ * The keychord will not be signalled if keys not in the keycode
+ * list are pressed.
+ * Keychords will not be signalled on key release events.
+ */
+struct input_keychord {
+	/* should be KEYCHORD_VERSION */
+	__u16 version;
+	/*
+	 * client specified ID, returned from read()
+	 * when this keychord is pressed.
+	 */
+	__u16 id;
+
+	/* number of keycodes in this keychord */
+	__u16 count;
+
+	/* variable length array of keycodes */
+	__u16 keycodes[];
+};
+
+#endif	/* __LINUX_KEYCHORD_H_ */