[PATCH] HID: core: move Usage Page concatenation to hid_parser_main()

[Nicolas Saenz Julienne]

As seen on some USB wireless keyboards manufactured by Primax, the HID
parser was using some assumptions that are not always true. In this case
it's s the fact that, inside the scope of a main item, an Usage Page
will always precede an Usage.

The spec is not pretty clear as 6.2.2.7 states "Any usage that follows
is interpreted as a Usage ID and concatenated with the Usage Page".
While 6.2.2.8 states "When the parser encounters a main item it
concatenates the last declared Usage Page with a Usage to form a
complete usage value." Being somewhat contradictory it was decided to
match Window's implementation, which follows 6.2.2.8.

In summary, the patch moves the Usage Page concatenation from the local
item parsing function to the main item parsing function.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
---

Note: A PR in hid-tools shoud show up anytime soon

 drivers/hid/hid-core.c | 30 ++++++++++++++++++------------
 include/linux/hid.h    |  1 +
 2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 9993b692598f..158468ef23a6 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -218,13 +218,14 @@ static unsigned hid_lookup_collection(struct hid_parser *parser, unsigned type)
  * Add a usage to the temporary parser table.
  */
 
-static int hid_add_usage(struct hid_parser *parser, unsigned usage)
+static int hid_add_usage(struct hid_parser *parser, unsigned usage, __u8 size)
 {
 	if (parser->local.usage_index >= HID_MAX_USAGES) {
 		hid_err(parser->device, "usage index exceeded\n");
 		return -1;
 	}
 	parser->local.usage[parser->local.usage_index] = usage;
+	parser->local.usage_size[parser->local.usage_index] = size;
 	parser->local.collection_index[parser->local.usage_index] =
 		parser->collection_stack_ptr ?
 		parser->collection_stack[parser->collection_stack_ptr - 1] : 0;
@@ -486,10 +487,7 @@ static int hid_parser_local(struct hid_parser *parser, struct hid_item *item)
 			return 0;
 		}
 
-		if (item->size <= 2)
-			data = (parser->global.usage_page << 16) + data;
-
-		return hid_add_usage(parser, data);
+		return hid_add_usage(parser, data, item->size);
 
 	case HID_LOCAL_ITEM_TAG_USAGE_MINIMUM:
 
@@ -498,9 +496,6 @@ static int hid_parser_local(struct hid_parser *parser, struct hid_item *item)
 			return 0;
 		}
 
-		if (item->size <= 2)
-			data = (parser->global.usage_page << 16) + data;
-
 		parser->local.usage_minimum = data;
 		return 0;
 
@@ -511,9 +506,6 @@ static int hid_parser_local(struct hid_parser *parser, struct hid_item *item)
 			return 0;
 		}
 
-		if (item->size <= 2)
-			data = (parser->global.usage_page << 16) + data;
-
 		count = data - parser->local.usage_minimum;
 		if (count + parser->local.usage_index >= HID_MAX_USAGES) {
 			/*
@@ -533,7 +525,7 @@ static int hid_parser_local(struct hid_parser *parser, struct hid_item *item)
 		}
 
 		for (n = parser->local.usage_minimum; n <= data; n++)
-			if (hid_add_usage(parser, n)) {
+			if (hid_add_usage(parser, n, item->size)) {
 				dbg_hid("hid_add_usage failed\n");
 				return -1;
 			}
@@ -553,8 +545,22 @@ static int hid_parser_local(struct hid_parser *parser, struct hid_item *item)
 
 static int hid_parser_main(struct hid_parser *parser, struct hid_item *item)
 {
+	unsigned int usages;
 	__u32 data;
 	int ret;
+	int i;
+
+	usages = max_t(unsigned, parser->local.usage_index,
+				 parser->global.report_count);
+
+	/*
+	 * As per specification, 6.2.2.8:
+	 * "When the parser encounters a main item it concatenates the last
+	 * declared Usage Page with a Usage to form a complete usage value."
+	 */
+	for (i = 0; i < usages; i++)
+		if (parser->local.usage_size[i] <= 2)
+			parser->local.usage[i] += parser->global.usage_page << 16;
 
 	data = item_udata(item);
 
diff --git a/include/linux/hid.h b/include/linux/hid.h
index f9707d1dcb58..d1fb4b678873 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -417,6 +417,7 @@ struct hid_global {
 
 struct hid_local {
 	unsigned usage[HID_MAX_USAGES]; /* usage array */
+	__u8 usage_size[HID_MAX_USAGES]; /* usage size array */
 	unsigned collection_index[HID_MAX_USAGES]; /* collection index array */
 	unsigned usage_index;
 	unsigned usage_minimum;
-- 
2.21.0