mac80211: calculate beacon loss time accurately

Instead of using a fixed 2 second timeout, calculate beacon loss interval
from the advertised beacon interval and a frame count.  With this beacon
loss happens after N (default 7) consecutive frames are missed which
for a typical setup (100TU beacon interval) is ~700ms (or ~1/3 previous).

Signed-off-by: Sam Leffler <sleffler@chromium.org>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

2 files changed, 13 insertions, 4 deletions

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 3598abf21844..ff7bc307827b 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -349,6 +349,7 @@ struct ieee80211_if_managed {
         struct work_struct chswitch_work;
         struct work_struct beacon_connection_loss_work;
 
+        unsigned long beacon_timeout;
         unsigned long probe_timeout;
         int probe_send_count;
 
diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index 84e24df234e2..729aba49cf98 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -31,10 +31,15 @@
 #define IEEE80211_MAX_PROBE_TRIES 5
 
 /*
- * beacon loss detection timeout
- * XXX: should depend on beacon interval
+ * Beacon loss timeout is calculated as N frames times the
+ * advertised beacon interval.  This may need to be somewhat
+ * higher than what hardware might detect to account for
+ * delays in the host processing frames. But since we also
+ * probe on beacon miss before declaring the connection lost
+ * default to what we want.
  */
-#define IEEE80211_BEACON_LOSS_TIME      (2 * HZ)
+#define IEEE80211_BEACON_LOSS_COUNT     7
+
 /*
  * Time the connection can be idle before we probe
  * it to see if we can still talk to the AP.
@@ -121,7 +126,7 @@ void ieee80211_sta_reset_beacon_monitor(struct ieee80211_sub_if_data *sdata)
                 return;
 
         mod_timer(&sdata->u.mgd.bcn_mon_timer,
-                  round_jiffies_up(jiffies + IEEE80211_BEACON_LOSS_TIME));
+                  round_jiffies_up(jiffies + sdata->u.mgd.beacon_timeout));
 }
 
 void ieee80211_sta_reset_conn_monitor(struct ieee80211_sub_if_data *sdata)
@@ -871,6 +876,9 @@ static void ieee80211_set_associated(struct ieee80211_sub_if_data *sdata,
         bss_info_changed |= ieee80211_handle_bss_capability(sdata,
                 cbss->capability, bss->has_erp_value, bss->erp_value);
 
+        sdata->u.mgd.beacon_timeout = usecs_to_jiffies(ieee80211_tu_to_usec(
+                IEEE80211_BEACON_LOSS_COUNT * bss_conf->beacon_int));
+
         sdata->u.mgd.associated = cbss;
         memcpy(sdata->u.mgd.bssid, cbss->bssid, ETH_ALEN);