mt7601u: use EWMA to calculate avg_rssi

avr_rssi is not calculated correctly as we do not divide result
by 256 (mt76 sum avg_rssi1 and avg_rssi2 and divide by 512).
However dividing by 256 will make avg_rssi almost the same as
last rssi value - not really an average. So use EWMA to calculate
avg_rssi. I've chosen weight_rcp=4 to convergence quicker on signal
strength changes.
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Jakub Kicinski <kubakici@wp.pl>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/mediatek/mt7601u/mac.c

@@ -453,7 +453,7 @@ mt7601u_rx_monitor_beacon(struct mt7601u_dev *dev, struct mt7601u_rxwi *rxwi,
 {
 	dev->bcn_freq_off = rxwi->freq_off;
 	dev->bcn_phy_mode = FIELD_GET(MT_RXWI_RATE_PHY, rate);
-	dev->avg_rssi = (dev->avg_rssi * 15) / 16 + (rssi << 8);
+	ewma_rssi_add(&dev->avg_rssi, -rssi);
 }
 
 static int
@@ -503,7 +503,7 @@ u32 mt76_mac_process_rx(struct mt7601u_dev *dev, struct sk_buff *skb,
 	if (mt7601u_rx_is_our_beacon(dev, data))
 		mt7601u_rx_monitor_beacon(dev, rxwi, rate, rssi);
 	else if (rxwi->rxinfo & cpu_to_le32(MT_RXINFO_U2M))
-		dev->avg_rssi = (dev->avg_rssi * 15) / 16 + (rssi << 8);
+		ewma_rssi_add(&dev->avg_rssi, -rssi);
 	spin_unlock_bh(&dev->con_mon_lock);
 
 	return len;

drivers/net/wireless/mediatek/mt7601u/mt7601u.h

@@ -23,6 +23,7 @@
 #include <linux/completion.h>
 #include <net/mac80211.h>
 #include <linux/debugfs.h>
+#include <linux/average.h>
 
 #include "regs.h"
 
@@ -138,6 +139,8 @@ enum {
 	MT7601U_STATE_MORE_STATS,
 };
 
+DECLARE_EWMA(rssi, 10, 4);
+
 /**
  * struct mt7601u_dev - adapter structure
  * @lock:		protects @wcid->tx_rate.
@@ -220,7 +223,7 @@ struct mt7601u_dev {
 	s8 bcn_freq_off;
 	u8 bcn_phy_mode;
 
-	int avg_rssi; /* starts at 0 and converges */
+	struct ewma_rssi avg_rssi;
 
 	u8 agc_save;
 

drivers/net/wireless/mediatek/mt7601u/phy.c

@@ -975,6 +975,7 @@ void mt7601u_agc_restore(struct mt7601u_dev *dev)
 static void mt7601u_agc_tune(struct mt7601u_dev *dev)
 {
 	u8 val = mt7601u_agc_default(dev);
+	long avg_rssi;
 
 	if (test_bit(MT7601U_STATE_SCANNING, &dev->state))
 		return;
@@ -984,9 +985,12 @@ static void mt7601u_agc_tune(struct mt7601u_dev *dev)
 	 *	 Rssi updates are only on beacons and U2M so should work...
 	 */
 	spin_lock_bh(&dev->con_mon_lock);
-	if (dev->avg_rssi <= -70)
+	avg_rssi = ewma_rssi_read(&dev->avg_rssi);
+	WARN_ON_ONCE(avg_rssi == 0);
+	avg_rssi = -avg_rssi;
+	if (avg_rssi <= -70)
 		val -= 0x20;
-	else if (dev->avg_rssi <= -60)
+	else if (avg_rssi <= -60)
 		val -= 0x10;
 	spin_unlock_bh(&dev->con_mon_lock);
 
@@ -1102,7 +1106,7 @@ void mt7601u_phy_con_cal_onoff(struct mt7601u_dev *dev,
 	/* Start/stop collecting beacon data */
 	spin_lock_bh(&dev->con_mon_lock);
 	ether_addr_copy(dev->ap_bssid, info->bssid);
-	dev->avg_rssi = 0;
+	ewma_rssi_init(&dev->avg_rssi);
 	dev->bcn_freq_off = MT_FREQ_OFFSET_INVALID;
 	spin_unlock_bh(&dev->con_mon_lock);