2 files changed, 66 insertions, 6 deletions

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 241533e1bc03..b84126491ab1 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -745,6 +745,7 @@ struct ieee80211_local {
         int scan_channel_idx;
         int scan_ies_len;
 
+        unsigned long leave_oper_channel_time;
         enum mac80211_scan_state next_scan_state;
         struct delayed_work scan_work;
         struct ieee80211_sub_if_data *scan_sdata;
diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index b822dce97867..75a85978c3b3 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -14,6 +14,8 @@
 
 #include <linux/if_arp.h>
 #include <linux/rtnetlink.h>
+#include <linux/pm_qos_params.h>
+#include <net/sch_generic.h>
 #include <net/mac80211.h>
 
 #include "ieee80211_i.h"
@@ -321,6 +323,7 @@ static int ieee80211_start_sw_scan(struct ieee80211_local *local)
 
         ieee80211_offchannel_stop_beaconing(local);
 
+        local->leave_oper_channel_time = 0;
         local->next_scan_state = SCAN_DECISION;
         local->scan_channel_idx = 0;
 
@@ -425,11 +428,28 @@ static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
         return rc;
 }
 
+static unsigned long
+ieee80211_scan_get_channel_time(struct ieee80211_channel *chan)
+{
+        /*
+         * TODO: channel switching also consumes quite some time,
+         * add that delay as well to get a better estimation
+         */
+        if (chan->flags & IEEE80211_CHAN_PASSIVE_SCAN)
+                return IEEE80211_PASSIVE_CHANNEL_TIME;
+        return IEEE80211_PROBE_DELAY + IEEE80211_CHANNEL_TIME;
+}
+
 static int ieee80211_scan_state_decision(struct ieee80211_local *local,
                                          unsigned long *next_delay)
 {
         bool associated = false;
+        bool tx_empty = true;
+        bool bad_latency;
+        bool listen_int_exceeded;
+        unsigned long min_beacon_int = 0;
         struct ieee80211_sub_if_data *sdata;
+        struct ieee80211_channel *next_chan;
 
         /* if no more bands/channels left, complete scan and advance to the idle state */
         if (local->scan_channel_idx >= local->scan_req->n_channels) {
@@ -437,7 +457,11 @@ static int ieee80211_scan_state_decision(struct ieee80211_local *local,
                 return 1;
         }
 
-        /* check if at least one STA interface is associated */
+        /*
+         * check if at least one STA interface is associated,
+         * check if at least one STA interface has pending tx frames
+         * and grab the lowest used beacon interval
+         */
         mutex_lock(&local->iflist_mtx);
         list_for_each_entry(sdata, &local->interfaces, list) {
                 if (!ieee80211_sdata_running(sdata))
@@ -446,7 +470,16 @@ static int ieee80211_scan_state_decision(struct ieee80211_local *local,
                 if (sdata->vif.type == NL80211_IFTYPE_STATION) {
                         if (sdata->u.mgd.associated) {
                                 associated = true;
-                                break;
+
+                                if (sdata->vif.bss_conf.beacon_int <
+                                    min_beacon_int || min_beacon_int == 0)
+                                        min_beacon_int =
+                                                sdata->vif.bss_conf.beacon_int;
+
+                                if (!qdisc_all_tx_empty(sdata->dev)) {
+                                        tx_empty = false;
+                                        break;
+                                }
                         }
                 }
         }
@@ -455,11 +488,34 @@ static int ieee80211_scan_state_decision(struct ieee80211_local *local,
         if (local->scan_channel) {
                 /*
                  * we're currently scanning a different channel, let's
-                 * switch back to the operating channel now if at least
-                 * one interface is associated. Otherwise just scan the
-                 * next channel
+                 * see if we can scan another channel without interfering
+                 * with the current traffic situation.
+                 *
+                 * Since we don't know if the AP has pending frames for us
+                 * we can only check for our tx queues and use the current
+                 * pm_qos requirements for rx. Hence, if no tx traffic occurs
+                 * at all we will scan as many channels in a row as the pm_qos
+                 * latency allows us to. Additionally we also check for the
+                 * currently negotiated listen interval to prevent losing
+                 * frames unnecessarily.
+                 *
+                 * Otherwise switch back to the operating channel.
                  */
-                if (associated)
+                next_chan = local->scan_req->channels[local->scan_channel_idx];
+
+                bad_latency = time_after(jiffies +
+                                ieee80211_scan_get_channel_time(next_chan),
+                                local->leave_oper_channel_time +
+                                usecs_to_jiffies(pm_qos_requirement(PM_QOS_NETWORK_LATENCY)));
+
+                listen_int_exceeded = time_after(jiffies +
+                                ieee80211_scan_get_channel_time(next_chan),
+                                local->leave_oper_channel_time +
+                                usecs_to_jiffies(min_beacon_int * 1024) *
+                                local->hw.conf.listen_interval);
+
+                if (associated && ( !tx_empty || bad_latency ||
+                    listen_int_exceeded))
                         local->next_scan_state = SCAN_ENTER_OPER_CHANNEL;
                 else
                         local->next_scan_state = SCAN_SET_CHANNEL;
@@ -491,6 +547,9 @@ static void ieee80211_scan_state_leave_oper_channel(struct ieee80211_local *loca
         else
                 *next_delay = HZ / 10;
 
+        /* remember when we left the operating channel */
+        local->leave_oper_channel_time = jiffies;
+
         /* advance to the next channel to be scanned */
         local->next_scan_state = SCAN_SET_CHANNEL;
 }