[PATCH v3 1/3] HID: Use hid_parser for pre-scanning the report descriptors

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

The Win 8 detection is sufficiently complex to warrant use of the full
parser code, in spite of the inferred memory usage. Therefore, we can use
the existing HID parser in hid-core for hid_scan_report() by re-using the
code from hid_open_report(). hid_parser_global, hid_parser_local and
hid_parser_reserved does not have any side effects. We just need to
reimplement the MAIN_ITEM callback to have a proper parsing without side
effects.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
---

changes in v3:
- remove one remnant duplicate message
- amended commit message
- re-add initializer of hid->group (set to HID_GROUP_GENERIC)

changes in v2:
- moved "flags" processing in patch 2/3 (so use hid->group in this patch)
- hid_scan_report() is less verbose when errors are found in the descriptor
- hid_scan_report() is tolerant to parsing errors
- fixed usage_page handling in hid_scan_collection(), which fixes sensors detection
- amended commit message

 drivers/hid/hid-core.c | 102 +++++++++++++++++++++++++++++++------------------
 1 file changed, 64 insertions(+), 38 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 3efe19f..9fc1220 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -677,12 +677,52 @@ static u8 *fetch_item(__u8 *start, __u8 *end, struct hid_item *item)
 	return NULL;
 }
 
-static void hid_scan_usage(struct hid_device *hid, u32 usage)
+static void hid_scan_input_usage(struct hid_parser *parser, u32 usage)
 {
+	struct hid_device *hid = parser->device;
+
 	if (usage == HID_DG_CONTACTID)
 		hid->group = HID_GROUP_MULTITOUCH;
 }
 
+static void hid_scan_collection(struct hid_parser *parser, unsigned type)
+{
+	struct hid_device *hid = parser->device;
+
+	if (((parser->global.usage_page << 16) == HID_UP_SENSOR) &&
+	    type == HID_COLLECTION_PHYSICAL)
+		hid->group = HID_GROUP_SENSOR_HUB;
+}
+
+static int hid_scan_main(struct hid_parser *parser, struct hid_item *item)
+{
+	__u32 data;
+	int i;
+
+	data = item_udata(item);
+
+	switch (item->tag) {
+	case HID_MAIN_ITEM_TAG_BEGIN_COLLECTION:
+		hid_scan_collection(parser, data & 0xff);
+		break;
+	case HID_MAIN_ITEM_TAG_END_COLLECTION:
+		break;
+	case HID_MAIN_ITEM_TAG_INPUT:
+		for (i = 0; i < parser->local.usage_index; i++)
+			hid_scan_input_usage(parser, parser->local.usage[i]);
+		break;
+	case HID_MAIN_ITEM_TAG_OUTPUT:
+		break;
+	case HID_MAIN_ITEM_TAG_FEATURE:
+		break;
+	}
+
+	/* Reset the local parser environment */
+	memset(&parser->local, 0, sizeof(parser->local));
+
+	return 0;
+}
+
 /*
  * Scan a report descriptor before the device is added to the bus.
  * Sets device groups and other properties that determine what driver
@@ -690,48 +730,34 @@ static void hid_scan_usage(struct hid_device *hid, u32 usage)
  */
 static int hid_scan_report(struct hid_device *hid)
 {
-	unsigned int page = 0, delim = 0;
+	struct hid_parser *parser;
+	struct hid_item item;
 	__u8 *start = hid->dev_rdesc;
 	__u8 *end = start + hid->dev_rsize;
-	unsigned int u, u_min = 0, u_max = 0;
-	struct hid_item item;
+	static int (*dispatch_type[])(struct hid_parser *parser,
+				      struct hid_item *item) = {
+		hid_scan_main,
+		hid_parser_global,
+		hid_parser_local,
+		hid_parser_reserved
+	};
+
+	parser = vzalloc(sizeof(struct hid_parser));
+	if (!parser)
+		return -ENOMEM;
 
+	parser->device = hid;
 	hid->group = HID_GROUP_GENERIC;
-	while ((start = fetch_item(start, end, &item)) != NULL) {
-		if (item.format != HID_ITEM_FORMAT_SHORT)
-			return -EINVAL;
-		if (item.type == HID_ITEM_TYPE_GLOBAL) {
-			if (item.tag == HID_GLOBAL_ITEM_TAG_USAGE_PAGE)
-				page = item_udata(&item) << 16;
-		} else if (item.type == HID_ITEM_TYPE_LOCAL) {
-			if (delim > 1)
-				break;
-			u = item_udata(&item);
-			if (item.size <= 2)
-				u += page;
-			switch (item.tag) {
-			case HID_LOCAL_ITEM_TAG_DELIMITER:
-				delim += !!u;
-				break;
-			case HID_LOCAL_ITEM_TAG_USAGE:
-				hid_scan_usage(hid, u);
-				break;
-			case HID_LOCAL_ITEM_TAG_USAGE_MINIMUM:
-				u_min = u;
-				break;
-			case HID_LOCAL_ITEM_TAG_USAGE_MAXIMUM:
-				u_max = u;
-				for (u = u_min; u <= u_max; u++)
-					hid_scan_usage(hid, u);
-				break;
-			}
-		} else if (page == HID_UP_SENSOR &&
-			item.type == HID_ITEM_TYPE_MAIN &&
-			item.tag == HID_MAIN_ITEM_TAG_BEGIN_COLLECTION &&
-			(item_udata(&item) & 0xff) == HID_COLLECTION_PHYSICAL)
-			hid->group = HID_GROUP_SENSOR_HUB;
-	}
 
+	/*
+	 * The parsing is simpler than the one in hid_open_report() as we should
+	 * be robust against hid errors. Those errors will be raised by
+	 * hid_open_report() anyway.
+	 */
+	while ((start = fetch_item(start, end, &item)) != NULL)
+		dispatch_type[item.type](parser, &item);
+
+	vfree(parser);
 	return 0;
 }
 
-- 
1.8.3.1