1 files changed, 41 insertions, 17 deletions

diff --git a/drivers/net/wireless/iwlwifi/iwl-agn-rxon.c b/drivers/net/wireless/iwlwifi/iwl-agn-rxon.c
index 6c2adc58d65..dfdbea6e8f9 100644
--- a/drivers/net/wireless/iwlwifi/iwl-agn-rxon.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn-rxon.c
@@ -471,6 +471,7 @@ static void iwlagn_check_needed_chains(struct iwl_priv *priv,
         struct iwl_rxon_context *tmp;
         struct ieee80211_sta *sta;
         struct iwl_ht_config *ht_conf = &priv->current_ht_config;
+        struct ieee80211_sta_ht_cap *ht_cap;
         bool need_multiple;
 
         lockdep_assert_held(&priv->mutex);
@@ -479,23 +480,7 @@ static void iwlagn_check_needed_chains(struct iwl_priv *priv,
         case NL80211_IFTYPE_STATION:
                 rcu_read_lock();
                 sta = ieee80211_find_sta(vif, bss_conf->bssid);
-                if (sta) {
-                        struct ieee80211_sta_ht_cap *ht_cap = &sta->ht_cap;
-                        int maxstreams;
-
-                        maxstreams = (ht_cap->mcs.tx_params &
-                                      IEEE80211_HT_MCS_TX_MAX_STREAMS_MASK)
-                                        >> IEEE80211_HT_MCS_TX_MAX_STREAMS_SHIFT;
-                        maxstreams += 1;
-
-                        need_multiple = true;
-
-                        if ((ht_cap->mcs.rx_mask[1] == 0) &&
-                            (ht_cap->mcs.rx_mask[2] == 0))
-                                need_multiple = false;
-                        if (maxstreams <= 1)
-                                need_multiple = false;
-                } else {
+                if (!sta) {
                         /*
                          * If at all, this can only happen through a race
                          * when the AP disconnects us while we're still
@@ -503,7 +488,46 @@ static void iwlagn_check_needed_chains(struct iwl_priv *priv,
                          * will soon tell us about that.
                          */
                         need_multiple = false;
+                        rcu_read_unlock();
+                        break;
+                }
+
+                ht_cap = &sta->ht_cap;
+
+                need_multiple = true;
+
+                /*
+                 * If the peer advertises no support for receiving 2 and 3
+                 * stream MCS rates, it can't be transmitting them either.
+                 */
+                if (ht_cap->mcs.rx_mask[1] == 0 &&
+                    ht_cap->mcs.rx_mask[2] == 0) {
+                        need_multiple = false;
+                } else if (!(ht_cap->mcs.tx_params &
+                                                IEEE80211_HT_MCS_TX_DEFINED)) {
+                        /* If it can't TX MCS at all ... */
+                        need_multiple = false;
+                } else if (ht_cap->mcs.tx_params &
+                                                IEEE80211_HT_MCS_TX_RX_DIFF) {
+                        int maxstreams;
+
+                        /*
+                         * But if it can receive them, it might still not
+                         * be able to transmit them, which is what we need
+                         * to check here -- so check the number of streams
+                         * it advertises for TX (if different from RX).
+                         */
+
+                        maxstreams = (ht_cap->mcs.tx_params &
+                                 IEEE80211_HT_MCS_TX_MAX_STREAMS_MASK);
+                        maxstreams >>=
+                                IEEE80211_HT_MCS_TX_MAX_STREAMS_SHIFT;
+                        maxstreams += 1;
+
+                        if (maxstreams <= 1)
+                                need_multiple = false;
                 }
+
                 rcu_read_unlock();
                 break;
         case NL80211_IFTYPE_ADHOC: