wl1251: Fix queue stopping/waking for TX path

This patch was adapted from 06f7bc7d
(from linus's linux-2.6 tree of kernel.org)

here's the original message:
    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: Denis 'GNUtoo' Carikli <GNUtoo@no-log.org>
Acked-by: Kalle Valo <kvalo@adurom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/wl12xx/wl1251.h

@@ -272,6 +272,8 @@ struct wl1251 {
 	int irq;
 	bool use_eeprom;
 
+	spinlock_t wl_lock;
+
 	enum wl1251_state state;
 	struct mutex mutex;
 
@@ -399,7 +401,8 @@ void wl1251_disable_interrupts(struct wl1251 *wl);
 
 #define WL1251_DEFAULT_POWER_LEVEL 20
 
-#define WL1251_TX_QUEUE_MAX_LENGTH 20
+#define WL1251_TX_QUEUE_LOW_WATERMARK  10
+#define WL1251_TX_QUEUE_HIGH_WATERMARK 25
 
 #define WL1251_DEFAULT_BEACON_INT 100
 #define WL1251_DEFAULT_DTIM_PERIOD 1

drivers/net/wireless/wl12xx/wl1251_main.c

@@ -375,6 +375,7 @@ static void wl1251_filter_work(struct work_struct *work)
 static int wl1251_op_tx(struct ieee80211_hw *hw, struct sk_buff *skb)
 {
 	struct wl1251 *wl = hw->priv;
+	unsigned long flags;
 
 	skb_queue_tail(&wl->tx_queue, skb);
 
@@ -389,16 +390,13 @@ static int wl1251_op_tx(struct ieee80211_hw *hw, struct sk_buff *skb)
 	 * 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) >= WL1251_TX_QUEUE_MAX_LENGTH) {
+	if (skb_queue_len(&wl->tx_queue) >= WL1251_TX_QUEUE_HIGH_WATERMARK) {
 		wl1251_debug(DEBUG_TX, "op_tx: tx_queue full, stop queues");
-		ieee80211_stop_queues(wl->hw);
 
-		/*
-		 * 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);
 		wl->tx_queue_stopped = true;
+		spin_unlock_irqrestore(&wl->wl_lock, flags);
 	}
 
 	return NETDEV_TX_OK;

drivers/net/wireless/wl12xx/wl1251_tx.c

@@ -320,11 +320,6 @@ void wl1251_tx_work(struct work_struct *work)
 
 		ret = wl1251_tx_frame(wl, skb);
 		if (ret == -EBUSY) {
-			/* firmware buffer is full, stop queues */
-			wl1251_debug(DEBUG_TX, "tx_work: fw buffer full, "
-				     "stop queues");
-			ieee80211_stop_queues(wl->hw);
-			wl->tx_queue_stopped = true;
 			skb_queue_head(&wl->tx_queue, skb);
 			goto out;
 		} else if (ret < 0) {
@@ -447,6 +442,7 @@ void wl1251_tx_complete(struct wl1251 *wl)
 {
 	int i, result_index, num_complete = 0;
 	struct tx_result result[FW_TX_CMPLT_BLOCK_SIZE], *result_ptr;
+	unsigned long flags;
 
 	if (unlikely(wl->state != WL1251_STATE_ON))
 		return;
@@ -475,6 +471,20 @@ void wl1251_tx_complete(struct wl1251 *wl)
 		}
 	}
 
+	if (wl->tx_queue_stopped
+	    &&
+	    skb_queue_len(&wl->tx_queue) <= WL1251_TX_QUEUE_LOW_WATERMARK){
+
+		/* firmware buffer has space, restart queues */
+		wl1251_debug(DEBUG_TX, "tx_complete: waking queues");
+		spin_lock_irqsave(&wl->wl_lock, flags);
+		ieee80211_wake_queues(wl->hw);
+		wl->tx_queue_stopped = false;
+		spin_unlock_irqrestore(&wl->wl_lock, flags);
+		ieee80211_queue_work(wl->hw, &wl->tx_work);
+
+	}
+
 	/* Every completed frame needs to be acknowledged */
 	if (num_complete) {
 		/*