mac80211: Track Beacon signal strength and implement cqm events

Calculate a running average of the signal strength reported for Beacon
frames and indicate cqm events if the average value moves below or
above the configured threshold value (and filter out repetitive events
with by using the configured hysteresis).

Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/cfg.c

@@ -1415,9 +1415,6 @@ static int ieee80211_set_cqm_rssi_config(struct wiphy *wiphy,
 	struct ieee80211_vif *vif = &sdata->vif;
 	struct ieee80211_bss_conf *bss_conf = &vif->bss_conf;
 
-	if (!(local->hw.flags & IEEE80211_HW_SUPPORTS_CQM_RSSI))
-		return -EOPNOTSUPP;
-
 	if (rssi_thold == bss_conf->cqm_rssi_thold &&
 	    rssi_hyst == bss_conf->cqm_rssi_hyst)
 		return 0;
@@ -1425,6 +1422,12 @@ static int ieee80211_set_cqm_rssi_config(struct wiphy *wiphy,
 	bss_conf->cqm_rssi_thold = rssi_thold;
 	bss_conf->cqm_rssi_hyst = rssi_hyst;
 
+	if (!(local->hw.flags & IEEE80211_HW_SUPPORTS_CQM_RSSI)) {
+		if (sdata->vif.type != NL80211_IFTYPE_STATION)
+			return -EOPNOTSUPP;
+		return 0;
+	}
+
 	/* tell the driver upon association, unless already associated */
 	if (sdata->u.mgd.associated)
 		ieee80211_bss_info_change_notify(sdata, BSS_CHANGED_CQM);

net/mac80211/debugfs_netdev.c

@@ -95,6 +95,14 @@ static ssize_t ieee80211_if_fmt_##name(					\
 	return scnprintf(buf, buflen, "%pM\n", sdata->field);		\
 }
 
+#define IEEE80211_IF_FMT_DEC_DIV_16(name, field)			\
+static ssize_t ieee80211_if_fmt_##name(					\
+	const struct ieee80211_sub_if_data *sdata,			\
+	char *buf, int buflen)						\
+{									\
+	return scnprintf(buf, buflen, "%d\n", sdata->field / 16);	\
+}
+
 #define __IEEE80211_IF_FILE(name, _write)				\
 static ssize_t ieee80211_if_read_##name(struct file *file,		\
 					char __user *userbuf,		\
@@ -135,6 +143,8 @@ IEEE80211_IF_FILE(rc_rateidx_mask_5ghz, rc_rateidx_mask[IEEE80211_BAND_5GHZ],
 /* STA attributes */
 IEEE80211_IF_FILE(bssid, u.mgd.bssid, MAC);
 IEEE80211_IF_FILE(aid, u.mgd.aid, DEC);
+IEEE80211_IF_FILE(last_beacon, u.mgd.last_beacon_signal, DEC);
+IEEE80211_IF_FILE(ave_beacon, u.mgd.ave_beacon_signal, DEC_DIV_16);
 
 static int ieee80211_set_smps(struct ieee80211_sub_if_data *sdata,
 			      enum ieee80211_smps_mode smps_mode)
@@ -271,6 +281,8 @@ static void add_sta_files(struct ieee80211_sub_if_data *sdata)
 
 	DEBUGFS_ADD(bssid);
 	DEBUGFS_ADD(aid);
+	DEBUGFS_ADD(last_beacon);
+	DEBUGFS_ADD(ave_beacon);
 	DEBUGFS_ADD_MODE(smps, 0600);
 }
 

net/mac80211/ieee80211_i.h

@@ -317,6 +317,7 @@ enum ieee80211_sta_flags {
 	IEEE80211_STA_MFP_ENABLED	= BIT(6),
 	IEEE80211_STA_UAPSD_ENABLED	= BIT(7),
 	IEEE80211_STA_NULLFUNC_ACKED	= BIT(8),
+	IEEE80211_STA_RESET_SIGNAL_AVE	= BIT(9),
 };
 
 struct ieee80211_if_managed {
@@ -359,6 +360,24 @@ struct ieee80211_if_managed {
 	int wmm_last_param_set;
 
 	u8 use_4addr;
+
+	/* Signal strength from the last Beacon frame in the current BSS. */
+	int last_beacon_signal;
+
+	/*
+	 * Weighted average of the signal strength from Beacon frames in the
+	 * current BSS. This is in units of 1/16 of the signal unit to maintain
+	 * accuracy and to speed up calculations, i.e., the value need to be
+	 * divided by 16 to get the actual value.
+	 */
+	int ave_beacon_signal;
+
+	/*
+	 * Last Beacon frame signal strength average (ave_beacon_signal / 16)
+	 * that triggered a cqm event. 0 indicates that no event has been
+	 * generated for the current association.
+	 */
+	int last_cqm_event_signal;
 };
 
 enum ieee80211_ibss_request {

net/mac80211/mlme.c

@@ -46,6 +46,13 @@
  */
 #define IEEE80211_PROBE_WAIT		(HZ / 2)
 
+/*
+ * Weight given to the latest Beacon frame when calculating average signal
+ * strength for Beacon frames received in the current BSS. This must be
+ * between 1 and 15.
+ */
+#define IEEE80211_SIGNAL_AVE_WEIGHT	3
+
 #define TMR_RUNNING_TIMER	0
 #define TMR_RUNNING_CHANSW	1
 
@@ -732,6 +739,8 @@ static void ieee80211_set_associated(struct ieee80211_sub_if_data *sdata,
 	sdata->u.mgd.associated = cbss;
 	memcpy(sdata->u.mgd.bssid, cbss->bssid, ETH_ALEN);
 
+	sdata->u.mgd.flags |= IEEE80211_STA_RESET_SIGNAL_AVE;
+
 	/* just to be sure */
 	sdata->u.mgd.flags &= ~(IEEE80211_STA_CONNECTION_POLL |
 				IEEE80211_STA_BEACON_POLL);
@@ -1347,6 +1356,7 @@ static void ieee80211_rx_mgmt_beacon(struct ieee80211_sub_if_data *sdata,
 				     struct ieee80211_rx_status *rx_status)
 {
 	struct ieee80211_if_managed *ifmgd = &sdata->u.mgd;
+	struct ieee80211_bss_conf *bss_conf = &sdata->vif.bss_conf;
 	size_t baselen;
 	struct ieee802_11_elems elems;
 	struct ieee80211_local *local = sdata->local;
@@ -1382,6 +1392,41 @@ static void ieee80211_rx_mgmt_beacon(struct ieee80211_sub_if_data *sdata,
 	if (memcmp(bssid, mgmt->bssid, ETH_ALEN) != 0)
 		return;
 
+	/* Track average RSSI from the Beacon frames of the current AP */
+	ifmgd->last_beacon_signal = rx_status->signal;
+	if (ifmgd->flags & IEEE80211_STA_RESET_SIGNAL_AVE) {
+		ifmgd->flags &= ~IEEE80211_STA_RESET_SIGNAL_AVE;
+		ifmgd->ave_beacon_signal = rx_status->signal;
+		ifmgd->last_cqm_event_signal = 0;
+	} else {
+		ifmgd->ave_beacon_signal =
+			(IEEE80211_SIGNAL_AVE_WEIGHT * rx_status->signal * 16 +
+			 (16 - IEEE80211_SIGNAL_AVE_WEIGHT) *
+			 ifmgd->ave_beacon_signal) / 16;
+	}
+	if (bss_conf->cqm_rssi_thold &&
+	    !(local->hw.flags & IEEE80211_HW_SUPPORTS_CQM_RSSI)) {
+		int sig = ifmgd->ave_beacon_signal / 16;
+		int last_event = ifmgd->last_cqm_event_signal;
+		int thold = bss_conf->cqm_rssi_thold;
+		int hyst = bss_conf->cqm_rssi_hyst;
+		if (sig < thold &&
+		    (last_event == 0 || sig < last_event - hyst)) {
+			ifmgd->last_cqm_event_signal = sig;
+			ieee80211_cqm_rssi_notify(
+				&sdata->vif,
+				NL80211_CQM_RSSI_THRESHOLD_EVENT_LOW,
+				GFP_KERNEL);
+		} else if (sig > thold &&
+			   (last_event == 0 || sig > last_event + hyst)) {
+			ifmgd->last_cqm_event_signal = sig;
+			ieee80211_cqm_rssi_notify(
+				&sdata->vif,
+				NL80211_CQM_RSSI_THRESHOLD_EVENT_HIGH,
+				GFP_KERNEL);
+		}
+	}
+
 	if (ifmgd->flags & IEEE80211_STA_BEACON_POLL) {
 #ifdef CONFIG_MAC80211_VERBOSE_DEBUG
 		if (net_ratelimit()) {