[PATCH 12/20] Input: MT - Add slot assignment by id

["Henrik Rydberg" <rydberg@xxxxxxxxxxx>]

Some drivers produce their own tracking ids, which needs to be mapped
to slots. This patch provides that function.

Signed-off-by: Henrik Rydberg <rydberg@xxxxxxxxxxx>
---
 drivers/input/input-mt.c | 30 ++++++++++++++++++++++++++++++
 include/linux/input/mt.h |  2 ++
 2 files changed, 32 insertions(+)

diff --git a/drivers/input/input-mt.c b/drivers/input/input-mt.c
index effea9b..a485014 100644
--- a/drivers/input/input-mt.c
+++ b/drivers/input/input-mt.c
@@ -383,3 +383,33 @@ int input_mt_assign_slots(struct input_dev *dev, int *slots,
 	return 0;
 }
 EXPORT_SYMBOL(input_mt_assign_slots);
+
+/**
+ * input_mt_assign_slot_by_id() - return matching slot
+ * @dev: input device with allocated MT slots
+ * @id: the sought tracking id
+ *
+ * Returns the slot of the given tracking id, if it exists. Otherwise,
+ * the first unused slot is returned.
+ *
+ * If no available slot can be found, -1 is returned.
+ */
+int input_mt_assign_slot_by_id(struct input_dev *dev, int id)
+{
+	struct input_mt *mt = dev->mt;
+	struct input_mt_slot *s;
+
+	if (!mt)
+		return -1;
+
+	for (s = mt->slots; s != mt->slots + mt->num_slots; s++)
+		if (input_mt_get_value(s, ABS_MT_TRACKING_ID) == id)
+			return s - mt->slots;
+
+	for (s = mt->slots; s != mt->slots + mt->num_slots; s++)
+		if (!input_mt_is_active(s))
+			return s - mt->slots;
+
+	return -1;
+}
+EXPORT_SYMBOL(input_mt_assign_slot_by_id);
diff --git a/include/linux/input/mt.h b/include/linux/input/mt.h
index 10bb77c..54b640b 100644
--- a/include/linux/input/mt.h
+++ b/include/linux/input/mt.h
@@ -109,4 +109,6 @@ struct input_mt_pos {
 int input_mt_assign_slots(struct input_dev *dev, int *slots,
 			  const struct input_mt_pos *pos, int num_pos);
 
+int input_mt_assign_slot_by_id(struct input_dev *dev, int id);
+
 #endif
-- 
1.7.12

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