mwl8k: Reserve buffers for tx management frames

Since queues are not stopped anymore, management frames would be
dropped if the corresponding tx queue is full.
This can cause issues say when we want to setup an ampdu stream and
action frames i.e addba requests keep getting dropped frequently.
Fix this by reserving some buffers to allow management frames to
go through in queue full conditions.

Signed-off-by: Nishant Sarmukadam <nishants@marvell.com>
Signed-off-by: Pradeep Nemavat <pnemavat@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/mwl8k.c

@@ -1818,6 +1818,7 @@ mwl8k_txq_xmit(struct ieee80211_hw *hw, int index, struct sk_buff *skb)
 	u8 tid = 0;
 	struct mwl8k_ampdu_stream *stream = NULL;
 	bool start_ba_session = false;
+	bool mgmtframe = false;
 	struct ieee80211_mgmt *mgmt = (struct ieee80211_mgmt *)skb->data;
 
 	wh = (struct ieee80211_hdr *)skb->data;
@@ -1826,6 +1827,9 @@ mwl8k_txq_xmit(struct ieee80211_hw *hw, int index, struct sk_buff *skb)
 	else
 		qos = 0;
 
+	if (ieee80211_is_mgmt(wh->frame_control))
+		mgmtframe = true;
+
 	if (priv->ap_fw)
 		mwl8k_encapsulate_tx_frame(skb);
 	else
@@ -1955,15 +1959,26 @@ mwl8k_txq_xmit(struct ieee80211_hw *hw, int index, struct sk_buff *skb)
 
 	txq = priv->txq + index;
 
-	if (txq->len >= MWL8K_TX_DESCS) {
-		if (start_ba_session) {
-			spin_lock(&priv->stream_lock);
-			mwl8k_remove_stream(hw, stream);
-			spin_unlock(&priv->stream_lock);
+	/* Mgmt frames that go out frequently are probe
+	 * responses. Other mgmt frames got out relatively
+	 * infrequently. Hence reserve 2 buffers so that
+	 * other mgmt frames do not get dropped due to an
+	 * already queued probe response in one of the
+	 * reserved buffers.
+	 */
+
+	if (txq->len >= MWL8K_TX_DESCS - 2) {
+		if (mgmtframe == false ||
+			txq->len == MWL8K_TX_DESCS) {
+			if (start_ba_session) {
+				spin_lock(&priv->stream_lock);
+				mwl8k_remove_stream(hw, stream);
+				spin_unlock(&priv->stream_lock);
+			}
+			spin_unlock_bh(&priv->tx_lock);
+			dev_kfree_skb(skb);
+			return;
 		}
-		spin_unlock_bh(&priv->tx_lock);
-		dev_kfree_skb(skb);
-		return;
 	}
 
 	BUG_ON(txq->skb[txq->tail] != NULL);