ath5k: keep beacon RSSI average

Keep an exponentially weighted moving average of the beacon RSSI in our BSS.
It will be used by the ANI implementation.

The averaging algorithm is copied from rt2x00, Thanks :)

Signed-off-by: Bruno Randolf <br1@einfach.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath5k/ath5k.h

@@ -992,6 +992,15 @@ struct ath5k_nfcal_hist
 	s16 nfval[ATH5K_NF_CAL_HIST_MAX];	/* last few noise floors */
 };
 
+/**
+ * struct avg_val - Helper structure for average calculation
+ * @avg: contains the actual average value
+ * @avg_weight: is used internally during calculation to prevent rounding errors
+ */
+struct ath5k_avg_val {
+	int avg;
+	int avg_weight;
+};
 
 /***************************************\
   HARDWARE ABSTRACTION LAYER STRUCTURE
@@ -1096,6 +1105,9 @@ struct ath5k_hw {
 
 	struct ath5k_nfcal_hist ah_nfcal_hist;
 
+	/* average beacon RSSI in our BSS (used by ANI) */
+	struct ath5k_avg_val	ah_beacon_rssi_avg;
+
 	/* noise floor from last periodic calibration */
 	s32			ah_noise_floor;
 
@@ -1305,4 +1317,27 @@ static inline u32 ath5k_hw_bitswap(u32 val, unsigned int bits)
 	return retval;
 }
 
+#define AVG_SAMPLES	8
+#define AVG_FACTOR	1000
+
+/**
+ * ath5k_moving_average -  Exponentially weighted moving average
+ * @avg: average structure
+ * @val: current value
+ *
+ * This implementation make use of a struct ath5k_avg_val to prevent rounding
+ * errors.
+ */
+static inline struct ath5k_avg_val
+ath5k_moving_average(const struct ath5k_avg_val avg, const int val)
+{
+	struct ath5k_avg_val new;
+	new.avg_weight = avg.avg_weight  ?
+		(((avg.avg_weight * ((AVG_SAMPLES) - 1)) +
+			(val * (AVG_FACTOR))) / (AVG_SAMPLES)) :
+		(val * (AVG_FACTOR));
+	new.avg = new.avg_weight / (AVG_FACTOR);
+	return new;
+}
+
 #endif

drivers/net/wireless/ath/ath5k/base.c

@@ -1803,6 +1803,25 @@ ath5k_check_ibss_tsf(struct ath5k_softc *sc, struct sk_buff *skb,
 	}
 }
 
+static void
+ath5k_update_beacon_rssi(struct ath5k_softc *sc, struct sk_buff *skb, int rssi)
+{
+	struct ieee80211_mgmt *mgmt = (struct ieee80211_mgmt *)skb->data;
+	struct ath5k_hw *ah = sc->ah;
+	struct ath_common *common = ath5k_hw_common(ah);
+
+	/* only beacons from our BSSID */
+	if (!ieee80211_is_beacon(mgmt->frame_control) ||
+	    memcmp(mgmt->bssid, common->curbssid, ETH_ALEN) != 0)
+		return;
+
+	ah->ah_beacon_rssi_avg = ath5k_moving_average(ah->ah_beacon_rssi_avg,
+						      rssi);
+
+	/* in IBSS mode we should keep RSSI statistics per neighbour */
+	/* le16_to_cpu(mgmt->u.beacon.capab_info) & WLAN_CAPABILITY_IBSS */
+}
+
 /*
  * Compute padding position. skb must contains an IEEE 802.11 frame
  */
@@ -2022,6 +2041,8 @@ ath5k_tasklet_rx(unsigned long data)
 
 		ath5k_debug_dump_skb(sc, skb, "RX  ", 0);
 
+		ath5k_update_beacon_rssi(sc, skb, rs.rs_rssi);
+
 		/* check beacons in IBSS mode */
 		if (sc->opmode == NL80211_IFTYPE_ADHOC)
 			ath5k_check_ibss_tsf(sc, skb, rxs);