rt2x00usb: Zero USB padding before sending URB

When USB driver requires padding at the end of frame or URB it will report
this need by increasing return value of get_tx_data_len callback. Common
USB code uses that return value as desired URB length.

Ensure that appropriate part of skb's tailroom exists and is zeroed.
Signed-off-by: Jakub Kicinski <kubakici@wp.pl>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
--
 drivers/net/wireless/rt2x00/rt2x00usb.c |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)
Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2x00usb.c

@@ -298,12 +298,22 @@ static bool rt2x00usb_kick_tx_entry(struct queue_entry *entry, void* data)
 		return false;
 
 	/*
-	 * USB devices cannot blindly pass the skb->len as the
-	 * length of the data to usb_fill_bulk_urb. Pass the skb
-	 * to the driver to determine what the length should be.
+	 * USB devices require certain padding at the end of each frame
+	 * and urb. Those paddings are not included in skbs. Pass entry
+	 * to the driver to determine what the overall length should be.
 	 */
 	length = rt2x00dev->ops->lib->get_tx_data_len(entry);
 
+	status = skb_padto(entry->skb, length);
+	if (unlikely(status)) {
+		/* TODO: report something more appropriate than IO_FAILED. */
+		WARNING(rt2x00dev, "TX SKB padding error, out of memory\n");
+		set_bit(ENTRY_DATA_IO_FAILED, &entry->flags);
+		rt2x00lib_dmadone(entry);
+
+		return false;
+	}
+
 	usb_fill_bulk_urb(entry_priv->urb, usb_dev,
 			  usb_sndbulkpipe(usb_dev, entry->queue->usb_endpoint),
 			  entry->skb->data, length,