Input: estimate number of events per packet

Calculate a default based on the number of ABS axes, REL axes,
and MT slots for the device during input device registration.
Signed-off-by: Jeff Brown <jeffbrown@android.com>
Reviewed-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/input.c

@@ -1746,6 +1746,42 @@ void input_set_capability(struct input_dev *dev, unsigned int type, unsigned int
 }
 EXPORT_SYMBOL(input_set_capability);
 
+static unsigned int input_estimate_events_per_packet(struct input_dev *dev)
+{
+	int mt_slots;
+	int i;
+	unsigned int events;
+
+	if (dev->mtsize) {
+		mt_slots = dev->mtsize;
+	} else if (test_bit(ABS_MT_TRACKING_ID, dev->absbit)) {
+		mt_slots = dev->absinfo[ABS_MT_TRACKING_ID].maximum -
+			   dev->absinfo[ABS_MT_TRACKING_ID].minimum + 1,
+		clamp(mt_slots, 2, 32);
+	} else if (test_bit(ABS_MT_POSITION_X, dev->absbit)) {
+		mt_slots = 2;
+	} else {
+		mt_slots = 0;
+	}
+
+	events = mt_slots + 1; /* count SYN_MT_REPORT and SYN_REPORT */
+
+	for (i = 0; i < ABS_CNT; i++) {
+		if (test_bit(i, dev->absbit)) {
+			if (input_is_mt_axis(i))
+				events += mt_slots;
+			else
+				events++;
+		}
+	}
+
+	for (i = 0; i < REL_CNT; i++)
+		if (test_bit(i, dev->relbit))
+			events++;
+
+	return events;
+}
+
 #define INPUT_CLEANSE_BITMASK(dev, type, bits)				\
 	do {								\
 		if (!test_bit(EV_##type, dev->evbit))			\
@@ -1793,6 +1829,10 @@ int input_register_device(struct input_dev *dev)
 	/* Make sure that bitmasks not mentioned in dev->evbit are clean. */
 	input_cleanse_bitmasks(dev);
 
+	if (!dev->hint_events_per_packet)
+		dev->hint_events_per_packet =
+				input_estimate_events_per_packet(dev);
+
 	/*
 	 * If delay and period are pre-set by the driver, then autorepeating
 	 * is handled by the driver itself and we don't do it in input.c.

include/linux/input/mt.h

@@ -48,6 +48,12 @@ static inline void input_mt_slot(struct input_dev *dev, int slot)
 	input_event(dev, EV_ABS, ABS_MT_SLOT, slot);
 }
 
+static inline bool input_is_mt_axis(int axis)
+{
+	return axis == ABS_MT_SLOT ||
+		(axis >= ABS_MT_FIRST && axis <= ABS_MT_LAST);
+}
+
 void input_mt_report_slot_state(struct input_dev *dev,
 				unsigned int tool_type, bool active);