ath9k: fix race with IEEE80211_CONF_PS checks

There is a small window where the mac80211 changes the IEEE80211_CONF_PS
flag, and then informs the driver about the change. We have a race
condition if we are checking the flag in the same time. Avoid it by
introducing a local variable, and using that instead of checking the
IEEE80211_CONF_PS flag directly.

This fix the problem reported by Luis:
http://article.gmane.org/gmane.linux.kernel.wireless.general/34363

Changes-licensed-under: ISC
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/hw.c

@@ -2863,10 +2863,8 @@ void ath9k_ps_wakeup(struct ath_softc *sc)
 	if (++sc->ps_usecount != 1)
 		goto unlock;
 
-	if (sc->sc_ah->power_mode != ATH9K_PM_AWAKE) {
-		sc->sc_ah->restore_mode = sc->sc_ah->power_mode;
+	if (sc->sc_ah->power_mode != ATH9K_PM_AWAKE)
 		ath9k_hw_setpower_nolock(sc->sc_ah, ATH9K_PM_AWAKE);
-	}
 
  unlock:
 	spin_unlock_irqrestore(&sc->sc_pm_lock, flags);
@@ -2880,13 +2878,12 @@ void ath9k_ps_restore(struct ath_softc *sc)
 	if (--sc->ps_usecount != 0)
 		goto unlock;
 
-	if ((sc->hw->conf.flags & IEEE80211_CONF_PS) &&
-		!(sc->sc_flags & (SC_OP_WAIT_FOR_BEACON |
-				SC_OP_WAIT_FOR_CAB |
-				SC_OP_WAIT_FOR_PSPOLL_DATA |
-				SC_OP_WAIT_FOR_TX_ACK)))
-		ath9k_hw_setpower_nolock(sc->sc_ah,
-				      sc->sc_ah->restore_mode);
+	if (sc->ps_enabled &&
+	    !(sc->sc_flags & (SC_OP_WAIT_FOR_BEACON |
+			      SC_OP_WAIT_FOR_CAB |
+			      SC_OP_WAIT_FOR_PSPOLL_DATA |
+			      SC_OP_WAIT_FOR_TX_ACK)))
+		ath9k_hw_setpower_nolock(sc->sc_ah, ATH9K_PM_NETWORK_SLEEP);
 
  unlock:
 	spin_unlock_irqrestore(&sc->sc_pm_lock, flags);