mac80211: introduce beacon-only timing data

In order to be able to predict the next DTIM TBTT
in the driver, add the ability to use timing data
from beacons only with the new hardware flag
IEEE80211_HW_TIMING_BEACON_ONLY and the BSS info
value sync_dtim_count which is only valid if the
timing data came from a beacon. The data can only
come from a beacon, and if no beacon was received
before association it is updated later together
with the DTIM count notification.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -277,9 +277,16 @@ enum ieee80211_rssi_event {
  *	valid in station mode only if after the driver was notified
  *	with the %BSS_CHANGED_DTIM_PERIOD flag, will be non-zero then.
  * @sync_tsf: last beacon's/probe response's TSF timestamp (could be old
- *	as it may have been received during scanning long ago)
+ *	as it may have been received during scanning long ago). If the
+ *	HW flag %IEEE80211_HW_TIMING_BEACON_ONLY is set, then this can
+ *	only come from a beacon, but might not become valid until after
+ *	association when a beacon is received (which is notified with the
+ *	%BSS_CHANGED_DTIM flag.)
  * @sync_device_ts: the device timestamp corresponding to the sync_tsf,
  *	the driver/device can use this to calculate synchronisation
+ *	(see @sync_tsf)
+ * @sync_dtim_count: Only valid when %IEEE80211_HW_TIMING_BEACON_ONLY
+ *	is requested, see @sync_tsf/@sync_device_ts.
  * @beacon_int: beacon interval
  * @assoc_capability: capabilities taken from assoc resp
  * @basic_rates: bitmap of basic rates, each bit stands for an
@@ -331,6 +338,7 @@ struct ieee80211_bss_conf {
 	u16 assoc_capability;
 	u64 sync_tsf;
 	u32 sync_device_ts;
+	u8 sync_dtim_count;
 	u32 basic_rates;
 	int mcast_rate[IEEE80211_NUM_BANDS];
 	u16 ht_operation_mode;
@@ -1371,6 +1379,9 @@ struct ieee80211_tx_control {
  * @IEEE80211_HW_P2P_DEV_ADDR_FOR_INTF: Use the P2P Device address for any
  *	P2P Interface. This will be honoured even if more than one interface
  *	is supported.
+ *
+ * @IEEE80211_HW_TIMING_BEACON_ONLY: Use sync timing from beacon frames
+ *	only, to allow getting TBTT of a DTIM beacon.
  */
 enum ieee80211_hw_flags {
 	IEEE80211_HW_HAS_RATE_CONTROL			= 1<<0,
@@ -1399,6 +1410,7 @@ enum ieee80211_hw_flags {
 	IEEE80211_HW_TX_AMPDU_SETUP_IN_HW		= 1<<23,
 	IEEE80211_HW_SCAN_WHILE_IDLE			= 1<<24,
 	IEEE80211_HW_P2P_DEV_ADDR_FOR_INTF		= 1<<25,
+	IEEE80211_HW_TIMING_BEACON_ONLY			= 1<<26,
 };
 
 /**

net/mac80211/ieee80211_i.h

@@ -86,7 +86,7 @@ struct ieee80211_fragment_entry {
 
 
 struct ieee80211_bss {
-	u32 device_ts;
+	u32 device_ts_beacon, device_ts_presp;
 
 	bool wmm_used;
 	bool uapsd_supported;

net/mac80211/mlme.c

@@ -2567,6 +2567,17 @@ static void ieee80211_rx_mgmt_beacon(struct ieee80211_sub_if_data *sdata,
 		ieee80211_rx_bss_info(sdata, mgmt, len, rx_status, &elems);
 		ifmgd->assoc_data->have_beacon = true;
 		ifmgd->assoc_data->need_beacon = false;
+		if (local->hw.flags & IEEE80211_HW_TIMING_BEACON_ONLY) {
+			sdata->vif.bss_conf.sync_tsf =
+				le64_to_cpu(mgmt->u.beacon.timestamp);
+			sdata->vif.bss_conf.sync_device_ts =
+				rx_status->device_timestamp;
+			if (elems.tim)
+				sdata->vif.bss_conf.sync_dtim_count =
+					elems.tim->dtim_count;
+			else
+				sdata->vif.bss_conf.sync_dtim_count = 0;
+		}
 		/* continue assoc process */
 		ifmgd->assoc_data->timeout = jiffies;
 		run_again(ifmgd, ifmgd->assoc_data->timeout);
@@ -2725,7 +2736,7 @@ static void ieee80211_rx_mgmt_beacon(struct ieee80211_sub_if_data *sdata,
 
 	/*
 	 * If we haven't had a beacon before, tell the driver about the
-	 * DTIM period now.
+	 * DTIM period (and beacon timing if desired) now.
 	 */
 	if (!bss_conf->dtim_period) {
 		/* a few bogus AP send dtim_period = 0 or no TIM IE */
@@ -2733,6 +2744,19 @@ static void ieee80211_rx_mgmt_beacon(struct ieee80211_sub_if_data *sdata,
 			bss_conf->dtim_period = elems.tim->dtim_period ?: 1;
 		else
 			bss_conf->dtim_period = 1;
+
+		if (local->hw.flags & IEEE80211_HW_TIMING_BEACON_ONLY) {
+			sdata->vif.bss_conf.sync_tsf =
+				le64_to_cpu(mgmt->u.beacon.timestamp);
+			sdata->vif.bss_conf.sync_device_ts =
+				rx_status->device_timestamp;
+			if (elems.tim)
+				sdata->vif.bss_conf.sync_dtim_count =
+					elems.tim->dtim_count;
+			else
+				sdata->vif.bss_conf.sync_dtim_count = 0;
+		}
+
 		changed |= BSS_CHANGED_DTIM_PERIOD;
 	}
 
@@ -3712,10 +3736,33 @@ static int ieee80211_prep_connection(struct ieee80211_sub_if_data *sdata,
 		/* set timing information */
 		sdata->vif.bss_conf.beacon_int = cbss->beacon_interval;
 		rcu_read_lock();
-		ies = rcu_dereference(cbss->ies);
-		sdata->vif.bss_conf.sync_tsf = ies->tsf;
+		ies = rcu_dereference(cbss->beacon_ies);
+		if (ies) {
+			const u8 *tim_ie;
+
+			sdata->vif.bss_conf.sync_tsf = ies->tsf;
+			sdata->vif.bss_conf.sync_device_ts =
+				bss->device_ts_beacon;
+			tim_ie = cfg80211_find_ie(WLAN_EID_TIM,
+						  ies->data, ies->len);
+			if (tim_ie && tim_ie[1] >= 2)
+				sdata->vif.bss_conf.sync_dtim_count = tim_ie[2];
+			else
+				sdata->vif.bss_conf.sync_dtim_count = 0;
+		} else if (!(local->hw.flags &
+					IEEE80211_HW_TIMING_BEACON_ONLY)) {
+			ies = rcu_dereference(cbss->proberesp_ies);
+			/* must be non-NULL since beacon IEs were NULL */
+			sdata->vif.bss_conf.sync_tsf = ies->tsf;
+			sdata->vif.bss_conf.sync_device_ts =
+				bss->device_ts_presp;
+			sdata->vif.bss_conf.sync_dtim_count = 0;
+		} else {
+			sdata->vif.bss_conf.sync_tsf = 0;
+			sdata->vif.bss_conf.sync_device_ts = 0;
+			sdata->vif.bss_conf.sync_dtim_count = 0;
+		}
 		rcu_read_unlock();
-		sdata->vif.bss_conf.sync_device_ts = bss->device_ts;
 
 		/* tell driver about BSSID, basic rates and timing */
 		ieee80211_bss_info_change_notify(sdata,
@@ -4041,13 +4088,23 @@ int ieee80211_mgd_assoc(struct ieee80211_sub_if_data *sdata,
 		const u8 *tim_ie = cfg80211_find_ie(WLAN_EID_TIM,
 						    beacon_ies->data,
 						    beacon_ies->len);
+		u8 dtim_count = 0;
+
 		if (tim_ie && tim_ie[1] >= sizeof(struct ieee80211_tim_ie)) {
 			const struct ieee80211_tim_ie *tim;
 			tim = (void *)(tim_ie + 2);
 			ifmgd->dtim_period = tim->dtim_period;
+			dtim_count = tim->dtim_count;
 		}
 		assoc_data->have_beacon = true;
 		assoc_data->timeout = jiffies;
+
+		if (local->hw.flags & IEEE80211_HW_TIMING_BEACON_ONLY) {
+			sdata->vif.bss_conf.sync_tsf = beacon_ies->tsf;
+			sdata->vif.bss_conf.sync_device_ts =
+				bss->device_ts_beacon;
+			sdata->vif.bss_conf.sync_dtim_count = dtim_count;
+		}
 	} else {
 		assoc_data->timeout = jiffies;
 	}

net/mac80211/scan.c

@@ -80,7 +80,10 @@ ieee80211_bss_info_update(struct ieee80211_local *local,
 
 	bss = (void *)cbss->priv;
 
-	bss->device_ts = rx_status->device_timestamp;
+	if (beacon)
+		bss->device_ts_beacon = rx_status->device_timestamp;
+	else
+		bss->device_ts_presp = rx_status->device_timestamp;
 
 	if (elems->parse_error) {
 		if (beacon)

net/mac80211/trace.h

@@ -340,6 +340,7 @@ TRACE_EVENT(drv_bss_info_changed,
 		__field(u16, assoc_cap)
 		__field(u64, sync_tsf)
 		__field(u32, sync_device_ts)
+		__field(u8, sync_dtim_count)
 		__field(u32, basic_rates)
 		__array(int, mcast_rate, IEEE80211_NUM_BANDS)
 		__field(u16, ht_operation_mode)
@@ -379,6 +380,7 @@ TRACE_EVENT(drv_bss_info_changed,
 		__entry->assoc_cap = info->assoc_capability;
 		__entry->sync_tsf = info->sync_tsf;
 		__entry->sync_device_ts = info->sync_device_ts;
+		__entry->sync_dtim_count = info->sync_dtim_count;
 		__entry->basic_rates = info->basic_rates;
 		memcpy(__entry->mcast_rate, info->mcast_rate,
 		       sizeof(__entry->mcast_rate));