mac80211: support hardware TX fragmentation offload

The lower driver is notified when the fragmentation threshold changes
and upon a reconfig of the interface.

If the driver supports hardware TX fragmentation, don't fragment
packets in the stack.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 96c5943..b392876a 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1033,6 +1033,7 @@
 	struct ieee80211_radiotap_header *rthdr =
 		(struct ieee80211_radiotap_header *) skb->data;
 	struct ieee80211_supported_band *sband;
+	bool hw_frag;
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 	int ret = ieee80211_radiotap_iterator_init(&iterator, rthdr, skb->len,
 						   NULL);
@@ -1042,6 +1043,9 @@
 	info->flags |= IEEE80211_TX_INTFL_DONT_ENCRYPT;
 	tx->flags &= ~IEEE80211_TX_FRAGMENTED;
 
+	/* packet is fragmented in HW if we have a non-NULL driver callback */
+	hw_frag = (tx->local->ops->set_frag_threshold != NULL);
+
 	/*
 	 * for every radiotap entry that is present
 	 * (ieee80211_radiotap_iterator_next returns -ENOENT when no more
@@ -1078,7 +1082,8 @@
 			}
 			if (*iterator.this_arg & IEEE80211_RADIOTAP_F_WEP)
 				info->flags &= ~IEEE80211_TX_INTFL_DONT_ENCRYPT;
-			if (*iterator.this_arg & IEEE80211_RADIOTAP_F_FRAG)
+			if ((*iterator.this_arg & IEEE80211_RADIOTAP_F_FRAG) &&
+								!hw_frag)
 				tx->flags |= IEEE80211_TX_FRAGMENTED;
 			break;
 
@@ -1181,8 +1186,10 @@
 	/*
 	 * Set this flag (used below to indicate "automatic fragmentation"),
 	 * it will be cleared/left by radiotap as desired.
+	 * Only valid when fragmentation is done by the stack.
 	 */
-	tx->flags |= IEEE80211_TX_FRAGMENTED;
+	if (!local->ops->set_frag_threshold)
+		tx->flags |= IEEE80211_TX_FRAGMENTED;
 
 	/* process and remove the injection radiotap header */
 	if (unlikely(info->flags & IEEE80211_TX_INTFL_HAS_RADIOTAP)) {