cfg80211: Scan results to also report the per chain signal strength

This commit enhances the scan results to report the per chain signal
strength based on the latest BSS update. This provides similar
information to what is already available through STA information.

Signed-off-by: Sunil Dutt <[e-mail]>
Signed-off-by: Jouni Malinen <[e-mail]>
Signed-off-by: Johannes Berg <[e-mail]>

include/net/cfg80211.h

···
  *	by %parent_bssid.
  * @parent_bssid: the BSS according to which %parent_tsf is set. This is set to
  *	the BSS that requested the scan in which the beacon/probe was received.
+ * @chains: bitmask for filled values in @chain_signal.
+ * @chain_signal: per-chain signal strength of last received BSS in dBm.
  */
 struct cfg80211_inform_bss {
 	struct ieee80211_channel *chan;
···
 	u64 boottime_ns;
 	u64 parent_tsf;
 	u8 parent_bssid[ETH_ALEN] __aligned(2);
+	u8 chains;
+	s8 chain_signal[IEEE80211_MAX_CHAINS];
 };
 
 /**
···
  *	that holds the beacon data. @beacon_ies is still valid, of course, and
  *	points to the same data as hidden_beacon_bss->beacon_ies in that case.
  * @signal: signal strength value (type depends on the wiphy's signal_type)
+ * @chains: bitmask for filled values in @chain_signal.
+ * @chain_signal: per-chain signal strength of last received BSS in dBm.
  * @priv: private area for driver use, has at least wiphy->bss_priv_size bytes
  */
 struct cfg80211_bss {
···
 	u16 capability;
 
 	u8 bssid[ETH_ALEN];
+	u8 chains;
+	s8 chain_signal[IEEE80211_MAX_CHAINS];
 
 	u8 priv[0] __aligned(sizeof(void *));
 };

include/uapi/linux/nl80211.h

···
  *	@NL80211_BSS_PARENT_BSSID. (u64).
  * @NL80211_BSS_PARENT_BSSID: the BSS according to which @NL80211_BSS_PARENT_TSF
  *	is set.
+ * @NL80211_BSS_CHAIN_SIGNAL: per-chain signal strength of last BSS update.
+ *	Contains a nested array of signal strength attributes (u8, dBm),
+ *	using the nesting index as the antenna number.
  * @__NL80211_BSS_AFTER_LAST: internal
  * @NL80211_BSS_MAX: highest BSS attribute
  */
···
 	NL80211_BSS_PAD,
 	NL80211_BSS_PARENT_TSF,
 	NL80211_BSS_PARENT_BSSID,
+	NL80211_BSS_CHAIN_SIGNAL,
 
 	/* keep last */
 	__NL80211_BSS_AFTER_LAST,

net/wireless/nl80211.c

···
 			      intbss->ts_boottime, NL80211_BSS_PAD))
 		goto nla_put_failure;
 
+	if (!nl80211_put_signal(msg, intbss->pub.chains,
+				intbss->pub.chain_signal,
+				NL80211_BSS_CHAIN_SIGNAL))
+		goto nla_put_failure;
+
 	switch (rdev->wiphy.signal_type) {
 	case CFG80211_SIGNAL_TYPE_MBM:
 		if (nla_put_u32(msg, NL80211_BSS_SIGNAL_MBM, res->signal))

net/wireless/scan.c

···
 		found->ts = tmp->ts;
 		found->ts_boottime = tmp->ts_boottime;
 		found->parent_tsf = tmp->parent_tsf;
+		found->pub.chains = tmp->pub.chains;
+		memcpy(found->pub.chain_signal, tmp->pub.chain_signal,
+		       IEEE80211_MAX_CHAINS);
 		ether_addr_copy(found->parent_bssid, tmp->parent_bssid);
 	} else {
 		struct cfg80211_internal_bss *new;
···
 	tmp.pub.capability = le16_to_cpu(mgmt->u.probe_resp.capab_info);
 	tmp.ts_boottime = data->boottime_ns;
 	tmp.parent_tsf = data->parent_tsf;
+	tmp.pub.chains = data->chains;
+	memcpy(tmp.pub.chain_signal, data->chain_signal, IEEE80211_MAX_CHAINS);
 	ether_addr_copy(tmp.parent_bssid, data->parent_bssid);
 
 	signal_valid = abs(data->chan->center_freq - channel->center_freq) <=