[RFC][PATCH] Input: Add infrastrucutre for monotonic event time stamps.

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Just wanted to send this out for some initial review and feedback.

As noted by Arve and others, since wall time can jump backwards, it
is difficult to use for input because one cannot determine if one
event occured before another or for how long a key was pressed.

However, the timestamp field is part of the kernel ABI, and cannot
be changed without possibly breaking existing users.

This patch adds a new IOCTL that sets a flag in the evdev_client
struct that will switch the timestamps to CLOCK_MONOTONIC instead
of CLOCK_REALTIME. This allows users of the evdev to specifiy
which clock id they want the timestamps to use.

The default remains CLOCK_REALTIME.

CC: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
CC: Daniel Kurtz <djkurtz@xxxxxxxxxx>
CC: linux-input@xxxxxxxxxxxxxxx
CC: Arve Hjønnevåg <arve@xxxxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
 drivers/input/evdev.c |   30 ++++++++++++++++++++++++++----
 include/linux/input.h |    2 ++
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index 4cf2534..6d04403 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -46,6 +46,7 @@ struct evdev_client {
 	struct fasync_struct *fasync;
 	struct evdev *evdev;
 	struct list_head node;
+	bool use_monotonic;
 	unsigned int bufsize;
 	struct input_event buffer[];
 };
@@ -54,8 +55,19 @@ static struct evdev *evdev_table[EVDEV_MINORS];
 static DEFINE_MUTEX(evdev_table_mutex);
 
 static void evdev_pass_event(struct evdev_client *client,
-			     struct input_event *event)
+			     struct input_event *event,
+			     ktime_t mono, ktime_t real)
 {
+	struct timespec ts;
+
+	if (client->use_monotonic)
+		ts = ktime_to_timespec(mono);
+	else
+		ts = ktime_to_timespec(real);
+	event->time.tv_sec = ts.tv_sec;
+	event->time.tv_usec = ts.tv_nsec / NSEC_PER_USEC;
+
+
 	/* Interrupts are disabled, just acquire the lock. */
 	spin_lock(&client->buffer_lock);
 
@@ -94,8 +106,11 @@ static void evdev_event(struct input_handle *handle,
 	struct evdev *evdev = handle->private;
 	struct evdev_client *client;
 	struct input_event event;
+	ktime_t time_mono, time_real;
+
+	time_mono = ktime_get();
+	time_real = ktime_sub(time_mono, ktime_get_monotonic_offset());
 
-	do_gettimeofday(&event.time);
 	event.type = type;
 	event.code = code;
 	event.value = value;
@@ -103,11 +118,12 @@ static void evdev_event(struct input_handle *handle,
 	rcu_read_lock();
 
 	client = rcu_dereference(evdev->grab);
+
 	if (client)
-		evdev_pass_event(client, &event);
+		evdev_pass_event(client, &event, time_mono, time_real);
 	else
 		list_for_each_entry_rcu(client, &evdev->client_list, node)
-			evdev_pass_event(client, &event);
+			evdev_pass_event(client, &event, time_mono, time_real);
 
 	rcu_read_unlock();
 
@@ -683,6 +699,12 @@ static long evdev_do_ioctl(struct file *file, unsigned int cmd,
 		else
 			return evdev_ungrab(evdev, client);
 
+	case EVIOCMONTIME:
+		if (copy_from_user(&i, p, sizeof(unsigned int)))
+			return -EFAULT;
+		client->use_monotonic = i;
+		return 0;
+
 	case EVIOCGKEYCODE:
 		return evdev_handle_get_keycode(dev, p);
 
diff --git a/include/linux/input.h b/include/linux/input.h
index 3862e32..245bfcc 100644
--- a/include/linux/input.h
+++ b/include/linux/input.h
@@ -129,6 +129,8 @@ struct input_keymap_entry {
 
 #define EVIOCGRAB		_IOW('E', 0x90, int)			/* Grab/Release device */
 
+#define EVIOCMONTIME		_IOW('E', 0xA0, int)			/* Set CLOCK_MONOTONIC Timestamps */
+
 /*
  * Device properties and quirks
  */
-- 
1.7.3.2.146.gca209

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