mac80211: add support for per-chain signal strength reporting

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
[fix unit documentation]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index c8447af..22e412b 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1372,6 +1372,7 @@
 	struct sk_buff *skb = rx->skb;
 	struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
+	int i;
 
 	if (!sta)
 		return RX_CONTINUE;
@@ -1422,6 +1423,19 @@
 		ewma_add(&sta->avg_signal, -status->signal);
 	}
 
+	if (status->chains) {
+		sta->chains = status->chains;
+		for (i = 0; i < ARRAY_SIZE(status->chain_signal); i++) {
+			int signal = status->chain_signal[i];
+
+			if (!(status->chains & BIT(i)))
+				continue;
+
+			sta->chain_signal_last[i] = signal;
+			ewma_add(&sta->chain_signal_avg[i], -signal);
+		}
+	}
+
 	/*
 	 * Change STA power saving mode only at the end of a frame
 	 * exchange sequence.