hostapd: Select a valid secondary channel if both enabled

When starting AP in HT40 mode and both HT40+ and HT40- options are
specified in hostapd.conf, select a valid secondary channel for the AP
automatically.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

hostapd/config_file.c

@@ -1106,6 +1106,10 @@ static int hostapd_config_ht_capab(struct hostapd_config *conf,
 		conf->ht_capab |= HT_CAP_INFO_SUPP_CHANNEL_WIDTH_SET;
 		conf->secondary_channel = 1;
 	}
+	if (os_strstr(capab, "[HT40+]") && os_strstr(capab, "[HT40-]")) {
+		conf->ht_capab |= HT_CAP_INFO_SUPP_CHANNEL_WIDTH_SET;
+		conf->ht40_plus_minus_allowed = 1;
+	}
 	if (os_strstr(capab, "[SMPS-STATIC]")) {
 		conf->ht_capab &= ~HT_CAP_INFO_SMPS_MASK;
 		conf->ht_capab |= HT_CAP_INFO_SMPS_STATIC;

src/ap/ap_config.h

@@ -724,6 +724,7 @@ struct hostapd_config {
 	u8 vht_oper_chwidth;
 	u8 vht_oper_centr_freq_seg0_idx;
 	u8 vht_oper_centr_freq_seg1_idx;
+	u8 ht40_plus_minus_allowed;
 
 	/* Use driver-generated interface addresses when adding multiple BSSs */
 	u8 use_driver_iface_addr;

src/ap/hw_features.c

@@ -722,14 +722,33 @@ static int hostapd_is_usable_chan(struct hostapd_iface *iface,
 
 static int hostapd_is_usable_chans(struct hostapd_iface *iface)
 {
+	int secondary_chan;
+
 	if (!hostapd_is_usable_chan(iface, iface->conf->channel, 1))
 		return 0;
 
 	if (!iface->conf->secondary_channel)
 		return 1;
 
-	return hostapd_is_usable_chan(iface, iface->conf->channel +
-				      iface->conf->secondary_channel * 4, 0);
+	if (!iface->conf->ht40_plus_minus_allowed)
+		return hostapd_is_usable_chan(
+			iface, iface->conf->channel +
+			iface->conf->secondary_channel * 4, 0);
+
+	/* Both HT40+ and HT40- are set, pick a valid secondary channel */
+	secondary_chan = iface->conf->channel + 4;
+	if (hostapd_is_usable_chan(iface, secondary_chan, 0)) {
+		iface->conf->secondary_channel = 1;
+		return 1;
+	}
+
+	secondary_chan = iface->conf->channel - 4;
+	if (hostapd_is_usable_chan(iface, secondary_chan, 0)) {
+		iface->conf->secondary_channel = -1;
+		return 1;
+	}
+
+	return 0;
 }