mac80211: Be more careful when changing channels.

If we cannot set the channel type, set the channel back to the
original.

Don't update the driver hardware if nothing actually changed.
Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/cfg.c

@@ -1215,6 +1215,9 @@ static int ieee80211_set_channel(struct wiphy *wiphy,
 {
 	struct ieee80211_local *local = wiphy_priv(wiphy);
 	struct ieee80211_sub_if_data *sdata = NULL;
+	struct ieee80211_channel *old_oper;
+	enum nl80211_channel_type old_oper_type;
+	enum nl80211_channel_type old_vif_oper_type= NL80211_CHAN_NO_HT;
 
 	if (netdev)
 		sdata = IEEE80211_DEV_TO_SUB_IF(netdev);
@@ -1232,13 +1235,23 @@ static int ieee80211_set_channel(struct wiphy *wiphy,
 		break;
 	}
 
-	local->oper_channel = chan;
+	if (sdata)
+		old_vif_oper_type = sdata->vif.bss_conf.channel_type;
+	old_oper_type = local->_oper_channel_type;
 
 	if (!ieee80211_set_channel_type(local, sdata, channel_type))
 		return -EBUSY;
 
-	ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_CHANNEL);
-	if (sdata && sdata->vif.type != NL80211_IFTYPE_MONITOR)
+	old_oper = local->oper_channel;
+	local->oper_channel = chan;
+
+	/* Update driver if changes were actually made. */
+	if ((old_oper != local->oper_channel) ||
+	    (old_oper_type != local->_oper_channel_type))
+		ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_CHANNEL);
+
+	if ((sdata && sdata->vif.type != NL80211_IFTYPE_MONITOR) &&
+	    old_vif_oper_type != sdata->vif.bss_conf.channel_type)
 		ieee80211_bss_info_change_notify(sdata, BSS_CHANGED_HT);
 
 	return 0;