ACS/DFS: Support min_tx_power configuration

If min_tx_power is specified (default 0 dBm, i.e., no constraint), ACS
and DFS will not consider channels whose available max_tx_power is less
than the configured value.

This may be useful to exclude SRD (Short Range Device) channels which
may be limited to 13.9 dBm (25 mW) in some regulatory domains.

Signed-off-by: Alan Young <consult.awy@gmail.com>

hostapd/config_file.c

@@ -3193,6 +3193,16 @@ static int hostapd_config_fill(struct hostapd_config *conf,
 		conf->acs_freq_list_present = 1;
 	} else if (os_strcmp(buf, "acs_exclude_6ghz_non_psc") == 0) {
 		conf->acs_exclude_6ghz_non_psc = atoi(pos);
+	} else if (os_strcmp(buf, "min_tx_power") == 0) {
+		int val = atoi(pos);
+
+		if (val < 0 || val > 255) {
+			wpa_printf(MSG_ERROR,
+				   "Line %d: invalid min_tx_power %d (expected 0..255)",
+				   line, val);
+			return 1;
+		}
+		conf->min_tx_power = val;
 	} else if (os_strcmp(buf, "beacon_int") == 0) {
 		int val = atoi(pos);
 		/* MIB defines range as 1..65535, but very small values

hostapd/hostapd.conf

@@ -225,6 +225,10 @@ channel=1
 # Default behavior is to include all PSC and non-PSC channels.
 #acs_exclude_6ghz_non_psc=1
 
+# Set minimum permitted max TX power (in dBm) for ACS and DFS channel selection.
+# (default 0, i.e., not constraint)
+#min_tx_power=20
+
 # Beacon interval in kus (1.024 ms) (default: 100; range 15..65535)
 beacon_int=100
 

src/ap/acs.c

@@ -546,6 +546,9 @@ static void acs_survey_mode_interference_factor(
 		if (!is_in_freqlist(iface, chan))
 			continue;
 
+		if (chan->max_tx_power < iface->conf->min_tx_power)
+			continue;
+
 		wpa_printf(MSG_DEBUG, "ACS: Survey analysis for channel %d (%d MHz)",
 			   chan->chan, chan->freq);
 
@@ -673,6 +676,9 @@ acs_find_ideal_chan_mode(struct hostapd_iface *iface,
 		if (!is_in_freqlist(iface, chan))
 			continue;
 
+		if (chan->max_tx_power < iface->conf->min_tx_power)
+			continue;
+
 		if (!chan_bw_allowed(chan, bw, 1, 1)) {
 			wpa_printf(MSG_DEBUG,
 				   "ACS: Channel %d: BW %u is not supported",
@@ -1047,6 +1053,9 @@ static int * acs_request_scan_add_freqs(struct hostapd_iface *iface,
 		if (!is_in_freqlist(iface, chan))
 			continue;
 
+		if (chan->max_tx_power < iface->conf->min_tx_power)
+			continue;
+
 		*freq++ = chan->freq;
 	}
 

src/ap/ap_config.h

@@ -953,6 +953,7 @@ struct hostapd_config {
 	struct wpa_freq_range_list acs_freq_list;
 	u8 acs_freq_list_present;
 	int acs_exclude_dfs;
+	u8 min_tx_power;
 	enum hostapd_hw_mode hw_mode; /* HOSTAPD_MODE_IEEE80211A, .. */
 	int acs_exclude_6ghz_non_psc;
 	enum {

src/ap/ap_drv_ops.c

@@ -888,7 +888,8 @@ static void hostapd_get_hw_mode_any_channels(struct hostapd_data *hapd,
 			continue;
 		if (!(chan->flag & HOSTAPD_CHAN_DISABLED) &&
 		    !(hapd->iface->conf->acs_exclude_dfs &&
-		      (chan->flag & HOSTAPD_CHAN_RADAR)))
+		      (chan->flag & HOSTAPD_CHAN_RADAR)) &&
+		    !(chan->max_tx_power < hapd->iface->conf->min_tx_power))
 			int_array_add_unique(freq_list, chan->freq);
 	}
 }

src/ap/dfs.c

@@ -246,6 +246,9 @@ static int dfs_find_channel(struct hostapd_iface *iface,
 			continue;
 		}
 
+		if (chan->max_tx_power < iface->conf->min_tx_power)
+			continue;
+
 		if (ret_chan && idx == channel_idx) {
 			wpa_printf(MSG_DEBUG, "Selected channel %d (%d)",
 				   chan->freq, chan->chan);