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>

drivers/hid/hid-core.c

@@ -172,6 +172,8 @@ static int open_collection(struct hid_parser *parser, unsigned type)
 	collection->type = type;
 	collection->usage = usage;
 	collection->level = parser->collection_stack_ptr - 1;
+	collection->parent = parser->active_collection;
+	parser->active_collection = collection;
 
 	if (type == HID_COLLECTION_APPLICATION)
 		parser->device->maxapplication++;
@@ -190,6 +192,8 @@ static int close_collection(struct hid_parser *parser)
 		return -EINVAL;
 	}
 	parser->collection_stack_ptr--;
+	if (parser->active_collection)
+		parser->active_collection = parser->active_collection->parent;
 	return 0;
 }
 

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;
 };