scan: use GET_SURVEY for SNR calculation in ranking

This issues a GET_SURVEY dump after scan results are available and
populates the survey information within the scan results. Currently
the only value obtained is the noise for a given frequency but the
survey results structure was created if in the future more values
need to be added.

From the noise, the SNR can be calculated. This is then used in the
ranking calculation to help lower BSS ranks that are on high noise
channels.

src/scan.c

@@ -132,6 +132,18 @@ struct scan_context {
 	 */
 	unsigned int get_fw_scan_cmd_id;
 	struct wiphy *wiphy;
+
+	unsigned int get_survey_cmd_id;
+};
+
+struct scan_survey {
+	int8_t noise;
+};
+
+struct scan_survey_results {
+	struct scan_survey survey_2_4[14];
+	struct scan_survey survey_5[196];
+	struct scan_survey survey_6[233];
 };
 
 struct scan_results {
@@ -140,6 +152,9 @@ struct scan_results {
 	uint64_t time_stamp;
 	struct scan_request *sr;
 	struct scan_freq_set *freqs;
+	struct scan_survey_results survey;
+
+	bool survey_parsed : 1;
 };
 
 static bool start_next_scan_request(struct wiphy_radio_work_item *item);
@@ -217,6 +232,9 @@ static void scan_context_free(struct scan_context *sc)
 	if (sc->get_fw_scan_cmd_id && nl80211)
 		l_genl_family_cancel(nl80211, sc->get_fw_scan_cmd_id);
 
+	if (sc->get_survey_cmd_id && nl80211)
+		l_genl_family_cancel(nl80211, sc->get_survey_cmd_id);
+
 	wiphy_state_watch_remove(sc->wiphy, sc->wiphy_watch_id);
 
 	l_free(sc);
@@ -1663,6 +1681,8 @@ static void scan_bss_compute_rank(struct scan_bss *bss)
 {
 	static const double RANK_HIGH_UTILIZATION_FACTOR = 0.8;
 	static const double RANK_LOW_UTILIZATION_FACTOR = 1.2;
+	static const double RANK_HIGH_SNR_FACTOR = 1.2;
+	static const double RANK_LOW_SNR_FACTOR = 0.8;
 	double rank;
 	uint32_t irank;
 	/*
@@ -1689,6 +1709,13 @@ static void scan_bss_compute_rank(struct scan_bss *bss)
 	else if (bss->utilization <= 63)
 		rank *= RANK_LOW_UTILIZATION_FACTOR;
 
+	if (bss->have_snr) {
+		if (bss->snr <= 15)
+			rank *= RANK_LOW_SNR_FACTOR;
+		else if (bss->snr >= 30)
+			rank *= RANK_HIGH_SNR_FACTOR;
+	}
+
 	irank = rank;
 
 	if (irank > USHRT_MAX)
@@ -1824,6 +1851,41 @@ int scan_bss_rank_compare(const void *a, const void *b, void *user_data)
 	return (bss->rank > new_bss->rank) ? 1 : -1;
 }
 
+static bool scan_survey_get_snr(struct scan_results *results,
+					uint32_t freq, int32_t signal,
+					int8_t *snr)
+{
+	uint8_t channel;
+	enum band_freq band;
+	int8_t noise = 0;
+
+	if (!results->survey_parsed)
+		return false;
+
+	channel = band_freq_to_channel(freq, &band);
+	if (L_WARN_ON(!channel))
+		return false;
+
+	switch (band) {
+	case BAND_FREQ_2_4_GHZ:
+		noise = results->survey.survey_2_4[channel].noise;
+		break;
+	case BAND_FREQ_5_GHZ:
+		noise = results->survey.survey_5[channel].noise;
+		break;
+	case BAND_FREQ_6_GHZ:
+		noise = results->survey.survey_6[channel].noise;
+		break;
+	}
+
+	if (noise) {
+		*snr = signal - noise;
+		return true;
+	}
+
+	return false;
+}
+
 static void get_scan_callback(struct l_genl_msg *msg, void *user_data)
 {
 	struct scan_results *results = user_data;
@@ -1849,6 +1911,10 @@ static void get_scan_callback(struct l_genl_msg *msg, void *user_data)
 		bss->time_stamp = results->time_stamp -
 					seen_ms_ago * L_USEC_PER_MSEC;
 
+	bss->have_snr = scan_survey_get_snr(results, bss->frequency,
+						bss->signal_strength / 100,
+						&bss->snr);
+
 	scan_bss_compute_rank(bss);
 	l_queue_insert(results->bss_list, bss, scan_bss_rank_compare, NULL);
 }
@@ -1925,11 +1991,88 @@ static void get_scan_done(void *user)
 	l_free(results);
 }
 
+static void get_survey_callback(struct l_genl_msg *msg, void *user_data)
+{
+	struct scan_results *results = user_data;
+	struct scan_survey_results *survey = &results->survey;
+	struct l_genl_attr attr;
+	uint32_t freq;
+	int8_t noise;
+	uint8_t channel;
+	enum band_freq band;
+
+	if (nl80211_parse_attrs(msg, NL80211_ATTR_SURVEY_INFO, &attr,
+				NL80211_ATTR_UNSPEC) < 0)
+		return;
+
+	if (nl80211_parse_nested(&attr, NL80211_ATTR_SURVEY_INFO,
+					NL80211_SURVEY_INFO_FREQUENCY, &freq,
+					NL80211_SURVEY_INFO_NOISE, &noise,
+					NL80211_ATTR_UNSPEC) < 0)
+		return;
+
+	channel = band_freq_to_channel(freq, &band);
+	if (!channel)
+		return;
+
+	/* At least one frequency was surveyed */
+	results->survey_parsed = true;
+
+	switch (band) {
+	case BAND_FREQ_2_4_GHZ:
+		survey->survey_2_4[channel].noise = noise;
+		break;
+	case BAND_FREQ_5_GHZ:
+		survey->survey_5[channel].noise = noise;
+		break;
+	case BAND_FREQ_6_GHZ:
+		survey->survey_6[channel].noise = noise;
+		break;
+	}
+}
+
+static void get_results(struct scan_results *results)
+{
+	struct l_genl_msg *scan_msg;
+
+	scan_msg = l_genl_msg_new_sized(NL80211_CMD_GET_SCAN, 8);
+
+	l_genl_msg_append_attr(scan_msg, NL80211_ATTR_WDEV, 8,
+					&results->sc->wdev_id);
+	results->sc->get_scan_cmd_id = l_genl_family_dump(nl80211, scan_msg,
+						get_scan_callback,
+						results, get_scan_done);
+}
+
+static void get_survey_done(void *user_data)
+{
+	struct scan_results *results = user_data;
+	struct scan_context *sc = results->sc;
+
+	sc->get_survey_cmd_id = 0;
+
+	get_results(results);
+}
+
+static bool scan_survey(struct scan_results *results)
+{
+	struct scan_context *sc = results->sc;
+	struct l_genl_msg *survey_msg;
+
+	survey_msg = l_genl_msg_new(NL80211_CMD_GET_SURVEY);
+	l_genl_msg_append_attr(survey_msg, NL80211_ATTR_WDEV, 8,
+				&sc->wdev_id);
+	sc->get_survey_cmd_id = l_genl_family_dump(nl80211, survey_msg,
+						get_survey_callback, results,
+						get_survey_done);
+
+	return sc->get_survey_cmd_id != 0;
+}
+
 static void scan_get_results(struct scan_context *sc, struct scan_request *sr,
 				struct scan_freq_set *freqs)
 {
 	struct scan_results *results;
-	struct l_genl_msg *scan_msg;
 
 	results = l_new(struct scan_results, 1);
 	results->sc = sc;
@@ -1938,13 +2081,12 @@ static void scan_get_results(struct scan_context *sc, struct scan_request *sr,
 	results->bss_list = l_queue_new();
 	results->freqs = freqs;
 
-	scan_msg = l_genl_msg_new_sized(NL80211_CMD_GET_SCAN, 8);
+	if (scan_survey(results))
+		return;
+	else
+		l_warn("failed to start a scan survey");
 
-	l_genl_msg_append_attr(scan_msg, NL80211_ATTR_WDEV, 8,
+	get_results(results);
-					&sc->wdev_id);
-	sc->get_scan_cmd_id = l_genl_family_dump(nl80211, scan_msg,
-						get_scan_callback,
-						results, get_scan_done);
 }
 
 static void scan_wiphy_watch(struct wiphy *wiphy,

src/scan.h

@@ -75,6 +75,7 @@ struct scan_bss {
 	uint64_t parent_tsf;
 	uint8_t *wfd;		/* Concatenated WFD IEs */
 	ssize_t wfd_size;	/* Size of Concatenated WFD IEs */
+	int8_t snr;
 	bool mde_present : 1;
 	bool cc_present : 1;
 	bool cap_rm_neighbor_report : 1;
@@ -89,6 +90,7 @@ struct scan_bss {
 	bool dpp_configurator : 1;
 	bool sae_pw_id_used : 1;
 	bool sae_pw_id_exclusive : 1;
+	bool have_snr : 1;
 };
 
 struct scan_parameters {