wl12xx: avoid starving the system hlid

Re-factor the Tx scheduler so that the system_hlid is taken into account
before restarting an iteration over the wlvifs. Previously this
hlid had a lower priority and would starve if some wlvif had many
packets.
In addition avoid iterating over wlvifs past last_wlvif when performing
the a second pass. If we had packets in those wlvifs they would have
been found earlier.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>

drivers/net/wireless/wl12xx/tx.c

@@ -572,6 +572,7 @@ static struct sk_buff *wl1271_skb_dequeue(struct wl1271 *wl)
 	struct wl12xx_vif *wlvif = wl->last_wlvif;
 	struct sk_buff *skb = NULL;
 
+	/* continue from last wlvif (round robin) */
 	if (wlvif) {
 		wl12xx_for_each_wlvif_continue(wl, wlvif) {
 			skb = wl12xx_vif_skb_dequeue(wl, wlvif);
@@ -582,20 +583,28 @@ static struct sk_buff *wl1271_skb_dequeue(struct wl1271 *wl)
 		}
 	}
 
-	/* do another pass */
+	/* dequeue from the system HLID before the restarting wlvif list */
+	if (!skb)
+		skb = wl12xx_lnk_skb_dequeue(wl, &wl->links[wl->system_hlid]);
+
+	/* do a new pass over the wlvif list */
 	if (!skb) {
 		wl12xx_for_each_wlvif(wl, wlvif) {
 			skb = wl12xx_vif_skb_dequeue(wl, wlvif);
 			if (skb) {
 				wl->last_wlvif = wlvif;
 				break;
 			}
+
+			/*
+			 * No need to continue after last_wlvif. The previous
+			 * pass should have found it.
+			 */
+			if (wlvif == wl->last_wlvif)
+				break;
 		}
 	}
 
-	if (!skb)
-		skb = wl12xx_lnk_skb_dequeue(wl, &wl->links[wl->system_hlid]);
-
 	if (!skb &&
 	    test_and_clear_bit(WL1271_FLAG_DUMMY_PACKET_PENDING, &wl->flags)) {
 		int q;