mac80211: add an rx flag for ignoring a packet's signal strength

For A-MPDU rx it makes sense to only process the signal strength once per
aggregate instead of once per subframe. Additonally, some hardware (e.g.
Atheros) only provides valid signal strength information for the last
subframe.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/net/mac80211.h

@@ -659,6 +659,8 @@ ieee80211_tx_info_clear_status(struct ieee80211_tx_info *info)
  * @RX_FLAG_HT: HT MCS was used and rate_idx is MCS index
  * @RX_FLAG_40MHZ: HT40 (40 MHz) was used
  * @RX_FLAG_SHORT_GI: Short guard interval was used
+ * @RX_FLAG_NO_SIGNAL_VAL: The signal strength value is not present.
+ *	Valid only for data frames (mainly A-MPDU)
  */
 enum mac80211_rx_flags {
 	RX_FLAG_MMIC_ERROR	= 1<<0,
@@ -672,6 +674,7 @@ enum mac80211_rx_flags {
 	RX_FLAG_HT		= 1<<9,
 	RX_FLAG_40MHZ		= 1<<10,
 	RX_FLAG_SHORT_GI	= 1<<11,
+	RX_FLAG_NO_SIGNAL_VAL	= 1<<12,
 };
 
 /**

net/mac80211/rx.c

@@ -177,7 +177,8 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
 	pos += 2;
 
 	/* IEEE80211_RADIOTAP_DBM_ANTSIGNAL */
-	if (local->hw.flags & IEEE80211_HW_SIGNAL_DBM) {
+	if (local->hw.flags & IEEE80211_HW_SIGNAL_DBM &&
+	    !(status->flag & RX_FLAG_NO_SIGNAL_VAL)) {
 		*pos = status->signal;
 		rthdr->it_present |=
 			cpu_to_le32(1 << IEEE80211_RADIOTAP_DBM_ANTSIGNAL);
@@ -1309,8 +1310,10 @@ ieee80211_rx_h_sta_process(struct ieee80211_rx_data *rx)
 
 	sta->rx_fragments++;
 	sta->rx_bytes += rx->skb->len;
+	if (!(status->flag & RX_FLAG_NO_SIGNAL_VAL)) {
 		sta->last_signal = status->signal;
 		ewma_add(&sta->avg_signal, -status->signal);
+	}
 
 	/*
 	 * Change STA power saving mode only at the end of a frame