mac80211: Do not generate CQM events based on first Beacon frames

The signal strength value in a single RX frame is not that reliable,
so it is better to delay start of CQM events until there is a real
average signal strength from more than a single Beacon frame
available.
Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/ieee80211_i.h

@@ -368,6 +368,13 @@ struct ieee80211_if_managed {
 	 */
 	int ave_beacon_signal;
 
+	/*
+	 * Number of Beacon frames used in ave_beacon_signal. This can be used
+	 * to avoid generating less reliable cqm events that would be based
+	 * only on couple of received frames.
+	 */
+	unsigned int count_beacon_signal;
+
 	/*
 	 * Last Beacon frame signal strength average (ave_beacon_signal / 16)
 	 * that triggered a cqm event. 0 indicates that no event has been

net/mac80211/mlme.c

@@ -54,6 +54,12 @@
  */
 #define IEEE80211_SIGNAL_AVE_WEIGHT	3
 
+/*
+ * How many Beacon frames need to have been used in average signal strength
+ * before starting to indicate signal change events.
+ */
+#define IEEE80211_SIGNAL_AVE_MIN_COUNT	4
+
 #define TMR_RUNNING_TIMER	0
 #define TMR_RUNNING_CHANSW	1
 
@@ -1555,13 +1561,16 @@ static void ieee80211_rx_mgmt_beacon(struct ieee80211_sub_if_data *sdata,
 		ifmgd->flags &= ~IEEE80211_STA_RESET_SIGNAL_AVE;
 		ifmgd->ave_beacon_signal = rx_status->signal * 16;
 		ifmgd->last_cqm_event_signal = 0;
+		ifmgd->count_beacon_signal = 1;
 	} else {
 		ifmgd->ave_beacon_signal =
 			(IEEE80211_SIGNAL_AVE_WEIGHT * rx_status->signal * 16 +
 			 (16 - IEEE80211_SIGNAL_AVE_WEIGHT) *
 			 ifmgd->ave_beacon_signal) / 16;
+		ifmgd->count_beacon_signal++;
 	}
 	if (bss_conf->cqm_rssi_thold &&
+	    ifmgd->count_beacon_signal >= IEEE80211_SIGNAL_AVE_MIN_COUNT &&
 	    !(local->hw.flags & IEEE80211_HW_SUPPORTS_CQM_RSSI)) {
 		int sig = ifmgd->ave_beacon_signal / 16;
 		int last_event = ifmgd->last_cqm_event_signal;