HID: core: store the collections as a basic tree

For each collection parsed, store a pointer to the parent collection
(if any). This makes it a lot easier to look up which collection(s)
any given item is part of

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Verified-by: Harry Cutts <hcutts@chromium.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
diff --git a/include/linux/hid.h b/include/linux/hid.h
index a355d61..fdfda89 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -427,6 +427,7 @@ struct hid_local {
  */
 
 struct hid_collection {
+	struct hid_collection *parent;
 	unsigned type;
 	unsigned usage;
 	unsigned level;
@@ -650,6 +651,7 @@ struct hid_parser {
 	unsigned int         *collection_stack;
 	unsigned int          collection_stack_ptr;
 	unsigned int          collection_stack_size;
+	struct hid_collection *active_collection;
 	struct hid_device    *device;
 	unsigned int          scan_flags;
 };