mac80211: dynamic PS - don't enter PS when TX frames are pending

Use the tx_frames_pending() driver callback to determine if Tx frames are
pending for its internal queues. If so postpone the dynamic PS timeout
to avoid interrupting Tx traffic.

The commit e8306f98 enabled this
behavior for drivers with IEEE80211_HW_PS_NULLFUNC_STACK. We enable this
for all drivers supporting dynamic PS.

This patch helps improve performance in noisy environments.
Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/mlme.c

@@ -760,9 +760,19 @@ void ieee80211_dynamic_ps_enable_work(struct work_struct *work)
 	if (local->hw.conf.flags & IEEE80211_CONF_PS)
 		return;
 
+	if (!local->disable_dynamic_ps &&
+	    local->hw.conf.dynamic_ps_timeout > 0) {
+		/* don't enter PS if TX frames are pending */
+		if (drv_tx_frames_pending(local)) {
+			mod_timer(&local->dynamic_ps_timer, jiffies +
+				  msecs_to_jiffies(
+				  local->hw.conf.dynamic_ps_timeout));
+			return;
+		}
+
 		/*
 		 * transmission can be stopped by others which leads to
-	 * dynamic_ps_timer expiry. Postpond the ps timer if it
+		 * dynamic_ps_timer expiry. Postpone the ps timer if it
 		 * is not the actual idle state.
 		 */
 		spin_lock_irqsave(&local->queue_stop_reason_lock, flags);
@@ -777,6 +787,7 @@ void ieee80211_dynamic_ps_enable_work(struct work_struct *work)
 			}
 		}
 		spin_unlock_irqrestore(&local->queue_stop_reason_lock, flags);
+	}
 
 	if ((local->hw.flags & IEEE80211_HW_PS_NULLFUNC_STACK) &&
 	    (!(ifmgd->flags & IEEE80211_STA_NULLFUNC_ACKED))) {
@@ -801,6 +812,7 @@ void ieee80211_dynamic_ps_enable_work(struct work_struct *work)
 		ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_PS);
 	}
 
+	if (local->hw.flags & IEEE80211_HW_PS_NULLFUNC_STACK)
 		netif_tx_wake_all_queues(sdata->dev);
 }