Input: MT - Get slot by key

Some devices use an internal key for tracking which cannot be directly
mapped to slots. This patch provides a key-to-slot mapping, which can
be used by drivers of such devices.

Reviewed-and-tested-by: Benjamin Tissoires <benjamin.tissoires@enac.fr>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>

2 files changed, 36 insertions, 0 deletions

diff --git a/drivers/input/input-mt.c b/drivers/input/input-mt.c
index caff298832a4..44f5a67aaa69 100644
--- a/drivers/input/input-mt.c
+++ b/drivers/input/input-mt.c
@@ -383,3 +383,35 @@ int input_mt_assign_slots(struct input_dev *dev, int *slots,
         return 0;
 }
 EXPORT_SYMBOL(input_mt_assign_slots);
+
+/**
+ * input_mt_get_slot_by_key() - return slot matching key
+ * @dev: input device with allocated MT slots
+ * @key: the key of the sought slot
+ *
+ * Returns the slot of the given key, if it exists, otherwise
+ * set the key on the first unused slot and return.
+ *
+ * If no available slot can be found, -1 is returned.
+ */
+int input_mt_get_slot_by_key(struct input_dev *dev, int key)
+{
+        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_is_active(s) && s->key == key)
+                        return s - mt->slots;
+
+        for (s = mt->slots; s != mt->slots + mt->num_slots; s++)
+                if (!input_mt_is_active(s)) {
+                        s->key = key;
+                        return s - mt->slots;
+                }
+
+        return -1;
+}
+EXPORT_SYMBOL(input_mt_get_slot_by_key);
diff --git a/include/linux/input/mt.h b/include/linux/input/mt.h
index 6b6f7c8e95bf..cc5cca774bab 100644
--- a/include/linux/input/mt.h
+++ b/include/linux/input/mt.h
@@ -24,10 +24,12 @@
  * struct input_mt_slot - represents the state of an input MT slot
  * @abs: holds current values of ABS_MT axes for this slot
  * @frame: last frame at which input_mt_report_slot_state() was called
+ * @key: optional driver designation of this slot
  */
 struct input_mt_slot {
         int abs[ABS_MT_LAST - ABS_MT_FIRST + 1];
         unsigned int frame;
+        unsigned int key;
 };
 
 /**
@@ -111,4 +113,6 @@ 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_get_slot_by_key(struct input_dev *dev, int key);
+
 #endif