ath9k: Update Beacon timers based on timestamp from the AP

Some APs seem to drift away from the expected TBTT (timestamp %
beacon_int_in_usec differs quite a bit from zero) which can result in
us waking up way too early to receive a Beacon frame. In order to work
around this, re-configure the Beacon timers after having received a
Beacon frame from the AP (i.e., when we know the offset between the
expected TBTT and the actual time the AP is sending out the Beacon
frame).
Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/ath9k.h

@@ -518,6 +518,7 @@ struct ath_rfkill {
 #define SC_OP_WAIT_FOR_CAB      BIT(16)
 #define SC_OP_WAIT_FOR_PSPOLL_DATA BIT(17)
 #define SC_OP_WAIT_FOR_TX_ACK   BIT(18)
+#define SC_OP_BEACON_SYNC       BIT(19)
 
 struct ath_bus_ops {
 	void		(*read_cachesize)(struct ath_softc *sc, int *csz);

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

@@ -487,7 +487,7 @@ static void ath9k_tasklet(unsigned long data)
 		 * the next Beacon.
 		 */
 		DPRINTF(sc, ATH_DBG_PS, "TSFOOR - Sync with next Beacon\n");
-		sc->sc_flags |= SC_OP_WAIT_FOR_BEACON;
+		sc->sc_flags |= SC_OP_WAIT_FOR_BEACON | SC_OP_BEACON_SYNC;
 	}
 
 	/* re-enable hardware interrupt */
@@ -914,6 +914,13 @@ static void ath9k_bss_assoc_info(struct ath_softc *sc,
 		if (avp->av_opmode == NL80211_IFTYPE_STATION) {
 			sc->curaid = bss_conf->aid;
 			ath9k_hw_write_associd(sc);
+
+			/*
+			 * Request a re-configuration of Beacon related timers
+			 * on the receipt of the first Beacon frame (i.e.,
+			 * after time sync with the AP).
+			 */
+			sc->sc_flags |= SC_OP_BEACON_SYNC;
 		}
 
 		/* Configure the beacon */

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

@@ -521,6 +521,13 @@ static void ath_rx_ps_beacon(struct ath_softc *sc, struct sk_buff *skb)
 	if (memcmp(sc->curbssid, mgmt->bssid, ETH_ALEN) != 0)
 		return; /* not from our current AP */
 
+	if (sc->sc_flags & SC_OP_BEACON_SYNC) {
+		sc->sc_flags &= ~SC_OP_BEACON_SYNC;
+		DPRINTF(sc, ATH_DBG_PS, "Reconfigure Beacon timers based on "
+			"timestamp from the AP\n");
+		ath_beacon_config(sc, NULL);
+	}
+
 	if (!(sc->hw->conf.flags & IEEE80211_CONF_PS)) {
 		/* We are not in PS mode anymore; remain awake */
 		DPRINTF(sc, ATH_DBG_PS, "Not in PS mode anymore, remain "