802.11n: scan for overlapping BSSes before starting 20/40 MHz channel

[wpasupplicant] / hostapd / hw_features.c

diff --git a/hostapd/hw_features.c b/hostapd/hw_features.c
index 3e6f7f2..22e1d83 100644 (file)
--- a/hostapd/hw_features.c
+++ b/hostapd/hw_features.c
@@ -236,6 +236,162 @@ static int ieee80211n_allowed_ht40_channel_pair(struct hostapd_iface *iface)
 }
 
 
+static void ieee80211n_switch_pri_sec(struct hostapd_iface *iface)
+{
+       if (iface->conf->secondary_channel > 0) {
+               iface->conf->channel += 4;
+               iface->conf->secondary_channel = -1;
+       } else {
+               iface->conf->channel -= 4;
+               iface->conf->secondary_channel = 1;
+       }
+}
+
+
+static int ieee80211n_check_40mhz_5g(struct hostapd_iface *iface)
+{
+       int pri_chan, sec_chan, pri_freq, sec_freq, pri_bss, sec_bss;
+       const struct hostapd_neighbor_bss *n;
+       size_t i, num;
+       int match;
+
+       pri_chan = iface->conf->channel;
+       sec_chan = iface->conf->secondary_channel * 4;
+       pri_freq = hostapd_hw_get_freq(iface->bss[0], pri_chan);
+       if (iface->conf->secondary_channel > 0)
+               sec_freq = pri_freq + 20;
+       else
+               sec_freq = pri_freq - 20;
+
+       n = hostapd_driver_get_neighbor_bss(iface->bss[0], &num);
+
+       /*
+        * Switch PRI/SEC channels if Beacons were detected on selected SEC
+        * channel, but not on selected PRI channel.
+        */
+       pri_bss = sec_bss = 0;
+       for (i = 0; n && i < num; i++) {
+               if (n[i].freq == pri_freq)
+                       pri_bss++;
+               else if (n[i].freq == sec_freq)
+                       sec_bss++;
+       }
+       if (sec_bss && !pri_bss) {
+               wpa_printf(MSG_INFO, "Switch own primary and secondary "
+                          "channel to get secondary channel with no Beacons "
+                          "from other BSSes");
+               ieee80211n_switch_pri_sec(iface);
+       }
+
+       /*
+        * Match PRI/SEC channel with any existing HT40 BSS on the same
+        * channels that we are about to use (if already mixed order in
+        * existing BSSes, use own preference).
+        */
+       match = 0;
+       for (i = 0; n && i < num; i++) {
+               if (pri_chan == n[i].pri_chan &&
+                   sec_chan == n[i].sec_chan) {
+                       match = 1;
+                       break;
+               }
+       }
+       if (!match) {
+               for (i = 0; n && i < num; i++) {
+                       if (pri_chan == n[i].sec_chan &&
+                           sec_chan == n[i].pri_chan) {
+                               wpa_printf(MSG_INFO, "Switch own primary and "
+                                          "secondary channel due to BSS "
+                                          "overlap with " MACSTR,
+                                          MAC2STR(n[i].bssid));
+                               ieee80211n_switch_pri_sec(iface);
+                               break;
+                       }
+               }
+       }
+
+       return 1;
+}
+
+
+static int ieee80211n_check_40mhz_2g4(struct hostapd_iface *iface)
+{
+       int pri_freq, sec_freq;
+       int affected_start, affected_end;
+       const struct hostapd_neighbor_bss *n;
+       size_t i, num;
+
+       pri_freq = hostapd_hw_get_freq(iface->bss[0], iface->conf->channel);
+       if (iface->conf->secondary_channel > 0)
+               sec_freq = pri_freq + 20;
+       else
+               sec_freq = pri_freq - 20;
+       affected_start = (pri_freq + sec_freq) / 2 - 25;
+       affected_end = (pri_freq + sec_freq) / 2 + 25;
+       wpa_printf(MSG_DEBUG, "40 MHz affected channel range: [%d,%d] MHz",
+                  affected_start, affected_end);
+       n = hostapd_driver_get_neighbor_bss(iface->bss[0], &num);
+       for (i = 0; n && i < num; i++) {
+               int pri = n[i].freq;
+               int sec = pri;
+               if (n[i].sec_chan) {
+                       if (n[i].sec_chan < n[i].pri_chan)
+                               sec = pri - 20;
+                       else
+                               sec = pri + 20;
+               }
+
+               if ((pri < affected_start || pri > affected_end) &&
+                   (sec < affected_start || sec > affected_end))
+                       continue; /* not within affected channel range */
+
+               if (n[i].sec_chan) {
+                       if (pri_freq != pri || sec_freq != sec) {
+                               wpa_printf(MSG_DEBUG, "40 MHz pri/sec "
+                                          "mismatch with BSS " MACSTR
+                                          " <%d,%d> (chan=%d%c) vs. <%d,%d>",
+                                          MAC2STR(n[i].bssid),
+                                          pri, sec, n[i].pri_chan,
+                                          sec > pri ? '+' : '-',
+                                          pri_freq, sec_freq);
+                               return 0;
+                       }
+               }
+
+               /* TODO: 40 MHz intolerant */
+       }
+
+       return 1;
+}
+
+
+static void ieee80211n_check_40mhz(struct hostapd_iface *iface)
+{
+       int oper40;
+
+       if (!iface->conf->secondary_channel)
+               return; /* HT40 not used */
+
+       /* Check list of neighboring BSSes (from scan) to see whether 40 MHz is
+        * allowed per IEEE 802.11n/D7.0, 11.14.3.2 */
+
+       if (iface->current_mode->mode == HOSTAPD_MODE_IEEE80211A)
+               oper40 = ieee80211n_check_40mhz_5g(iface);
+       else
+               oper40 = ieee80211n_check_40mhz_2g4(iface);
+
+       if (!oper40) {
+               wpa_printf(MSG_INFO, "20/40 MHz operation not permitted on "
+                          "channel pri=%d sec=%d based on overlapping BSSes",
+                          iface->conf->channel,
+                          iface->conf->channel +
+                          iface->conf->secondary_channel * 4);
+               iface->conf->secondary_channel = 0;
+               iface->conf->ht_capab &= ~HT_CAP_INFO_SUPP_CHANNEL_WIDTH_SET;
+       }
+}
+
+
 static int ieee80211n_supported_ht_capab(struct hostapd_iface *iface)
 {
        u16 hw = iface->current_mode->ht_capab;
@@ -402,6 +558,7 @@ int hostapd_select_hw_mode(struct hostapd_iface *iface)
        }
 
 #ifdef CONFIG_IEEE80211N
+       ieee80211n_check_40mhz(iface);
        if (!ieee80211n_allowed_ht40_channel_pair(iface))
                return -1;
        if (!ieee80211n_supported_ht_capab(iface))