Input: reset device timestamp on sync

We need to reset input device's timestamp on input_sync(), otherwise
drivers not using input_set_timestamp() will end up with a stale
timestamp after their clients consume first input event.

Fixes: 3b51c44b ("Input: allow drivers specify timestamp for input events")
Reported-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/input.c

@@ -397,6 +397,13 @@ static void input_handle_event(struct input_dev *dev,
 		if (dev->num_vals >= 2)
 			input_pass_values(dev, dev->vals, dev->num_vals);
 		dev->num_vals = 0;
+		/*
+		 * Reset the timestamp on flush so we won't end up
+		 * with a stale one. Note we only need to reset the
+		 * monolithic one as we use its presence when deciding
+		 * whether to generate a synthetic timestamp.
+		 */
+		dev->timestamp[INPUT_CLK_MONO] = ktime_set(0, 0);
 	} else if (dev->num_vals >= dev->max_vals - 2) {
 		dev->vals[dev->num_vals++] = input_value_sync;
 		input_pass_values(dev, dev->vals, dev->num_vals);