wl1271: Fix queue stopping/waking for TX path

The queue stopping/waking functionality was broken in a way that could
cause huge latencies in TX transfers and even cause the TX to stall in the
right circumstances. Correct these problems.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/wl12xx/wl1271_main.c b/drivers/net/wireless/wl12xx/wl1271_main.c
index 81fb02e..184264a 100644
--- a/drivers/net/wireless/wl12xx/wl1271_main.c
+++ b/drivers/net/wireless/wl12xx/wl1271_main.c
@@ -791,15 +791,13 @@
 	 * The workqueue is slow to process the tx_queue and we need stop
 	 * the queue here, otherwise the queue will get too long.
 	 */
-	if (skb_queue_len(&wl->tx_queue) >= WL1271_TX_QUEUE_MAX_LENGTH) {
-		ieee80211_stop_queues(wl->hw);
+	if (skb_queue_len(&wl->tx_queue) >= WL1271_TX_QUEUE_HIGH_WATERMARK) {
+		wl1271_debug(DEBUG_TX, "op_tx: stopping queues");
 
-		/*
-		 * FIXME: this is racy, the variable is not properly
-		 * protected. Maybe fix this by removing the stupid
-		 * variable altogether and checking the real queue state?
-		 */
+		spin_lock_irqsave(&wl->wl_lock, flags);
+		ieee80211_stop_queues(wl->hw);
 		set_bit(WL1271_FLAG_TX_QUEUE_STOPPED, &wl->flags);
+		spin_unlock_irqrestore(&wl->wl_lock, flags);
 	}
 
 	return NETDEV_TX_OK;