[RFC 2/2] mac80211: add improved HW queue control

[Johannes Berg <johannes@sipsolutions.net>]

From: Johannes Berg <johannes.berg@intel.com>



Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 include/net/mac80211.h     |   81 ++++++++++++++++++++++++++++++++++++++++++---
 net/mac80211/agg-tx.c      |   11 +++---
 net/mac80211/cfg.c         |    6 +++
 net/mac80211/ieee80211_i.h |    1 
 net/mac80211/iface.c       |   54 ++++++++++++++++++++++++++++++
 net/mac80211/main.c        |    5 ++
 net/mac80211/tx.c          |   38 ++++++++++++++++-----
 net/mac80211/util.c        |   48 +++++++++++++++++++++-----
 8 files changed, 216 insertions(+), 28 deletions(-)

--- a/include/net/mac80211.h	2012-03-28 10:39:22.000000000 +0200
+++ b/include/net/mac80211.h	2012-03-28 10:40:04.000000000 +0200
@@ -93,9 +93,11 @@
  * @IEEE80211_MAX_QUEUES: Maximum number of regular device queues.
  */
 enum ieee80211_max_queues {
-	IEEE80211_MAX_QUEUES =		4,
+	IEEE80211_MAX_QUEUES =		16,
 };
 
+#define IEEE80211_INVAL_HW_QUEUE	0xff
+
 /**
  * enum ieee80211_ac_numbers - AC numbers as used in mac80211
  * @IEEE80211_AC_VO: voice
@@ -520,7 +522,7 @@ struct ieee80211_tx_rate {
  *
  * @flags: transmit info flags, defined above
  * @band: the band to transmit on (use for checking for races)
- * @reserved: reserved for future use
+ * @hw_queue: HW queue to put the frame on, skb_get_queue_mapping() gives the AC
  * @ack_frame_id: internal frame ID for TX status, used internally
  * @control: union for control data
  * @status: union for status data
@@ -536,7 +538,7 @@ struct ieee80211_tx_info {
 	u32 flags;
 	u8 band;
 
-	u8 reserved;
+	u8 hw_queue;
 
 	u16 ack_frame_id;
 
@@ -887,6 +889,8 @@ enum ieee80211_vif_flags {
  *	these need to be set (or cleared) when the interface is added
  *	or, if supported by the driver, the interface type is changed
  *	at runtime, mac80211 will never touch this field
+ * @hw_queue: hardware queue for each AC
+ * @cab_queue: content-after-beacon (DTIM beacon really) queue, AP mode only
  * @drv_priv: data area for driver use, will always be aligned to
  *	sizeof(void *).
  */
@@ -895,7 +899,12 @@ struct ieee80211_vif {
 	struct ieee80211_bss_conf bss_conf;
 	u8 addr[ETH_ALEN];
 	bool p2p;
+
+	u8 cab_queue;
+	u8 hw_queue[IEEE80211_NUM_ACS];
+
 	u32 driver_flags;
+
 	/* must be last */
 	u8 drv_priv[0] __attribute__((__aligned__(sizeof(void *))));
 };
@@ -1177,6 +1186,11 @@ enum sta_notify_cmd {
  * @IEEE80211_HW_WANT_MONITOR_VIF: The driver would like to be informed of
  *	a virtual monitor interface when monitor interfaces are the only
  *	active interfaces.
+ *
+ * @IEEE80211_HW_QUEUE_CONTROL: The driver wants to control per-interface
+ *	queue mapping in order to use different queues (not just one per AC)
+ *	for different virtual interfaces. See the doc section on HW queue
+ *	control for more details.
  */
 enum ieee80211_hw_flags {
 	IEEE80211_HW_HAS_RATE_CONTROL			= 1<<0,
@@ -1199,7 +1213,7 @@ enum ieee80211_hw_flags {
 	IEEE80211_HW_SUPPORTS_UAPSD			= 1<<17,
 	IEEE80211_HW_REPORTS_TX_ACK_STATUS		= 1<<18,
 	IEEE80211_HW_CONNECTION_MONITOR			= 1<<19,
-	/* reuse bit 20 */
+	IEEE80211_HW_QUEUE_CONTROL			= 1<<20,
 	IEEE80211_HW_SUPPORTS_PER_STA_GTK		= 1<<21,
 	IEEE80211_HW_AP_LINK_PS				= 1<<22,
 	IEEE80211_HW_TX_AMPDU_SETUP_IN_HW		= 1<<23,
@@ -1269,6 +1283,9 @@ enum ieee80211_hw_flags {
  * @max_tx_aggregation_subframes: maximum number of subframes in an
  *	aggregate an HT driver will transmit, used by the peer as a
  *	hint to size its reorder buffer.
+ *
+ * @offchannel_tx_hw_queue: HW queue ID to use for offchannel TX
+ *	(if %IEEE80211_HW_QUEUE_CONTROL is set)
  */
 struct ieee80211_hw {
 	struct ieee80211_conf conf;
@@ -1289,6 +1306,7 @@ struct ieee80211_hw {
 	u8 max_rate_tries;
 	u8 max_rx_aggregation_subframes;
 	u8 max_tx_aggregation_subframes;
+	u8 offchannel_tx_hw_queue;
 };
 
 /**
@@ -1697,6 +1715,61 @@ void ieee80211_free_txskb(struct ieee802
  */
 
 /**
+ * DOC: HW queue control
+ *
+ * Before HW queue control was introduced, mac80211 only had a single static
+ * assignment of per-interface AC software queues to hardware queues. This
+ * was problematic for a few reasons:
+ * 1) off-channel transmissions might get stuck behind other frames
+ * 2) multiple virtual interfaces couldn't be handled correctly
+ * 3) after-DTIM frames could get stuck behind other frames
+ *
+ * To solve this, hardware typically uses multiple different queues for all
+ * the different usages, and this needs to be propagated into mac80211 so it
+ * won't have the same problem with the software queues.
+ *
+ * Therefore, mac80211 now offers the %IEEE80211_HW_QUEUE_CONTROL capability
+ * flag that tells it that the driver implements its own queue control. To do
+ * so, the driver will set up the various queues in each &struct ieee80211_vif
+ * and the offchannel queue in &struct ieee80211_hw. In response, mac80211 will
+ * use those queue IDs in the hw_queue field of &struct ieee80211_tx_info and
+ * if necessary will queue the frame on the right software queue that mirrors
+ * the hardware queue.
+ * Additionally, the driver has to then use these HW queue IDs for the queue
+ * management functions (ieee80211_stop_queue() et al.)
+ *
+ * The driver is free to set up the queue mappings as needed, multiple virtual
+ * interfaces may map to the same hardware queues if needed. The setup has to
+ * happen during add_interface or change_interface callbacks. For example, a
+ * driver supporting station+station and station+AP modes might decide to have
+ * 10 hardware queues to handle different scenarios:
+ *
+ * 4 AC HW queues for 1st vif: 0, 1, 2, 3
+ * 4 AC HW queues for 2nd vif: 4, 5, 6, 7
+ * after-DTIM queue for AP:   8
+ * off-channel queue:         9
+ *
+ * It would then set up the hardware like this:
+ *   hw.offchannel_tx_hw_queue = 9
+ *
+ * and the first virtual interface that is added as follows:
+ *   vif.hw_queue[IEEE80211_AC_VO] = 0
+ *   vif.hw_queue[IEEE80211_AC_VI] = 1
+ *   vif.hw_queue[IEEE80211_AC_BE] = 2
+ *   vif.hw_queue[IEEE80211_AC_BK] = 3
+ *   vif.cab_queue = 8 // if AP mode, otherwise %IEEE80211_INVAL_HW_QUEUE
+ * and the second virtual interface with 4-7.
+ *
+ * If queue 6 gets full, for example, mac80211 would only stop the second
+ * virtual interface's BE queue since virtual interface queues are per AC.
+ *
+ * Note that the vif.cab_queue value should be set to %IEEE80211_INVAL_HW_QUEUE
+ * whenever the queue is not used (i.e. the interface is not in AP mode) if the
+ * queue could potentially be shared since mac80211 will look at cab_queue when
+ * a queue is stopped/woken even if the interface is not in AP mode.
+ */
+
+/**
  * enum ieee80211_filter_flags - hardware filter flags
  *
  * These flags determine what the filter in hardware should be
--- a/net/mac80211/iface.c	2012-03-28 10:39:38.000000000 +0200
+++ b/net/mac80211/iface.c	2012-03-28 10:48:48.000000000 +0200
@@ -149,6 +149,26 @@ static int ieee80211_check_concurrent_if
 	return 0;
 }
 
+static int ieee80211_check_queues(struct ieee80211_sub_if_data *sdata)
+{
+	int i;
+
+	for (i = 0; i < IEEE80211_NUM_ACS; i++)
+		if (WARN_ON_ONCE(sdata->vif.hw_queue[i] ==
+				 IEEE80211_INVAL_HW_QUEUE))
+			return -EINVAL;
+
+	if (WARN_ON_ONCE(sdata->vif.type == NL80211_IFTYPE_AP &&
+			 sdata->vif.cab_queue == IEEE80211_INVAL_HW_QUEUE))
+		return -EINVAL;
+
+	if (WARN_ON_ONCE(sdata->vif.type != NL80211_IFTYPE_AP &&
+			 sdata->vif.cab_queue != IEEE80211_INVAL_HW_QUEUE))
+		return -EINVAL;
+
+	return 0;
+}
+
 void ieee80211_adjust_monitor_flags(struct ieee80211_sub_if_data *sdata,
 				    const int offset)
 {
@@ -169,6 +189,20 @@ void ieee80211_adjust_monitor_flags(stru
 #undef ADJUST
 }
 
+static void ieee80211_set_default_queues(struct ieee80211_sub_if_data *sdata)
+{
+	struct ieee80211_local *local = sdata->local;
+	int i;
+
+	for (i = 0; i < IEEE80211_NUM_ACS; i++) {
+		if (local->hw.flags & IEEE80211_HW_QUEUE_CONTROL)
+			sdata->vif.hw_queue[i] = IEEE80211_INVAL_HW_QUEUE;
+		else
+			sdata->vif.hw_queue[i] = i;
+	}
+	sdata->vif.cab_queue = IEEE80211_INVAL_HW_QUEUE;
+}
+
 static int ieee80211_add_virtual_monitor(struct ieee80211_local *local)
 {
 	struct ieee80211_sub_if_data *sdata;
@@ -190,6 +224,8 @@ static int ieee80211_add_virtual_monitor
 	snprintf(sdata->name, IFNAMSIZ, "%s-monitor",
 		 wiphy_name(local->hw.wiphy));
 
+	ieee80211_set_default_queues(sdata);
+
 	ret = drv_add_interface(local, sdata);
 	if (WARN_ON(ret)) {
 		/* ok .. stupid driver, it asked for this! */
@@ -197,6 +233,12 @@ static int ieee80211_add_virtual_monitor
 		return ret;
 	}
 
+	ret = ieee80211_check_queues(sdata);
+	if (ret) {
+		kfree(sdata);
+		return ret;
+	}
+
 	rcu_assign_pointer(local->monitor_sdata, sdata);
 
 	return 0;
@@ -344,6 +386,9 @@ static int ieee80211_do_open(struct net_
 			res = drv_add_interface(local, sdata);
 			if (res)
 				goto err_stop;
+			res = ieee80211_check_queues(sdata);
+			if (res)
+				goto err_stop;
 		}
 
 		if (sdata->vif.type == NL80211_IFTYPE_AP) {
@@ -1040,6 +1085,13 @@ static int ieee80211_runtime_change_ifty
 	if (ret)
 		type = sdata->vif.type;
 
+	/*
+	 * Ignore return value here, there's not much we can do since
+	 * the driver changed the interface type internally already.
+	 * The warnings will hopefully make driver authors fix it :-)
+	 */
+	ieee80211_check_queues(sdata);
+
 	ieee80211_setup_sdata(sdata, type);
 
 	err = ieee80211_do_open(sdata->dev, false);
@@ -1266,6 +1318,8 @@ int ieee80211_if_add(struct ieee80211_lo
 			       sizeof(sdata->rc_rateidx_mcs_mask[i]));
 	}
 
+	ieee80211_set_default_queues(sdata);
+
 	/* setup type-dependent data */
 	ieee80211_setup_sdata(sdata, type);
 
--- a/net/mac80211/util.c	2012-03-28 10:39:22.000000000 +0200
+++ b/net/mac80211/util.c	2012-03-28 10:48:27.000000000 +0200
@@ -265,11 +265,36 @@ __le16 ieee80211_ctstoself_duration(stru
 }
 EXPORT_SYMBOL(ieee80211_ctstoself_duration);
 
+void ieee80211_propagate_queue_wake(struct ieee80211_local *local, int queue)
+{
+	struct ieee80211_sub_if_data *sdata;
+
+	list_for_each_entry_rcu(sdata, &local->interfaces, list) {
+		int ac;
+
+		if (test_bit(SDATA_STATE_OFFCHANNEL, &sdata->state))
+			continue;
+
+		if (sdata->vif.cab_queue != IEEE80211_INVAL_HW_QUEUE &&
+		    local->queue_stop_reasons[sdata->vif.cab_queue] != 0)
+			continue;
+
+		for (ac = 0; ac < IEEE80211_NUM_ACS; ac++) {
+			int ac_queue = sdata->vif.hw_queue[ac];
+
+			if (ac_queue == queue ||
+			    (sdata->vif.cab_queue == queue &&
+			     local->queue_stop_reasons[ac_queue] == 0 &&
+			     skb_queue_empty(&local->pending[ac_queue])))
+				netif_wake_subqueue(sdata->dev, ac);
+		}
+	}
+}
+
 static void __ieee80211_wake_queue(struct ieee80211_hw *hw, int queue,
 				   enum queue_stop_reason reason)
 {
 	struct ieee80211_local *local = hw_to_local(hw);
-	struct ieee80211_sub_if_data *sdata;
 
 	trace_wake_queue(local, queue, reason);
 
@@ -287,11 +312,7 @@ static void __ieee80211_wake_queue(struc
 
 	if (skb_queue_empty(&local->pending[queue])) {
 		rcu_read_lock();
-		list_for_each_entry_rcu(sdata, &local->interfaces, list) {
-			if (test_bit(SDATA_STATE_OFFCHANNEL, &sdata->state))
-				continue;
-			netif_wake_subqueue(sdata->dev, queue);
-		}
+		ieee80211_propagate_queue_wake(local, queue);
 		rcu_read_unlock();
 	} else
 		tasklet_schedule(&local->tx_pending_tasklet);
@@ -332,8 +353,15 @@ static void __ieee80211_stop_queue(struc
 	__set_bit(reason, &local->queue_stop_reasons[queue]);
 
 	rcu_read_lock();
-	list_for_each_entry_rcu(sdata, &local->interfaces, list)
-		netif_stop_subqueue(sdata->dev, queue);
+	list_for_each_entry_rcu(sdata, &local->interfaces, list) {
+		int ac;
+
+		for (ac = 0; ac < IEEE80211_NUM_ACS; ac++) {
+			if (sdata->vif.hw_queue[ac] == queue ||
+			    sdata->vif.cab_queue == queue)
+				netif_stop_subqueue(sdata->dev, ac);
+		}
+	}
 	rcu_read_unlock();
 }
 
@@ -360,8 +388,8 @@ void ieee80211_add_pending_skb(struct ie
 {
 	struct ieee80211_hw *hw = &local->hw;
 	unsigned long flags;
-	int queue = skb_get_queue_mapping(skb);
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+	int queue = info->hw_queue;
 
 	if (WARN_ON(!info->control.vif)) {
 		kfree_skb(skb);
@@ -393,7 +421,7 @@ void ieee80211_add_pending_skbs_fn(struc
 			continue;
 		}
 
-		queue = skb_get_queue_mapping(skb);
+		queue = info->hw_queue;
 
 		__ieee80211_stop_queue(hw, queue,
 				IEEE80211_QUEUE_STOP_REASON_SKB_ADD);
--- a/net/mac80211/tx.c	2012-03-28 10:39:22.000000000 +0200
+++ b/net/mac80211/tx.c	2012-03-28 10:50:14.000000000 +0200
@@ -400,6 +400,8 @@ ieee80211_tx_h_multicast_ps_buf(struct i
 		return TX_CONTINUE;
 
 	info->flags |= IEEE80211_TX_CTL_SEND_AFTER_DTIM;
+	if (tx->local->hw.flags & IEEE80211_HW_QUEUE_CONTROL)
+		info->hw_queue = tx->sdata->vif.cab_queue;
 
 	/* device releases frame after DTIM beacon */
 	if (!(tx->local->hw.flags & IEEE80211_HW_HOST_BROADCAST_PS_BUFFERING))
@@ -1215,11 +1217,19 @@ static bool ieee80211_tx_frags(struct ie
 			       bool txpending)
 {
 	struct sk_buff *skb, *tmp;
-	struct ieee80211_tx_info *info;
 	unsigned long flags;
 
 	skb_queue_walk_safe(skbs, skb, tmp) {
-		int q = skb_get_queue_mapping(skb);
+		struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+		int q = info->hw_queue;
+
+#ifdef CONFIG_MAC80211_VERBOSE_DEBUG
+		if (WARN_ON_ONCE(q >= local->hw.queues)) {
+			__skb_unlink(skb, skbs);
+			dev_kfree_skb(skb);
+			continue;
+		}
+#endif
 
 		spin_lock_irqsave(&local->queue_stop_reason_lock, flags);
 		if (local->queue_stop_reasons[q] ||
@@ -1241,7 +1251,6 @@ static bool ieee80211_tx_frags(struct ie
 		}
 		spin_unlock_irqrestore(&local->queue_stop_reason_lock, flags);
 
-		info = IEEE80211_SKB_CB(skb);
 		info->control.vif = vif;
 		info->control.sta = sta;
 
@@ -1285,9 +1294,14 @@ static bool __ieee80211_tx(struct ieee80
 	switch (sdata->vif.type) {
 	case NL80211_IFTYPE_MONITOR:
 		sdata = rcu_dereference(local->monitor_sdata);
-		if (sdata)
+		if (sdata) {
 			vif = &sdata->vif;
-		else
+			info->hw_queue =
+				vif->hw_queue[skb_get_queue_mapping(skb)];
+		} else if (local->hw.flags & IEEE80211_HW_QUEUE_CONTROL) {
+			dev_kfree_skb(skb);
+			return true;
+		} else
 			vif = NULL;
 		break;
 	case NL80211_IFTYPE_AP_VLAN:
@@ -1403,6 +1417,12 @@ static bool ieee80211_tx(struct ieee8021
 	tx.channel = local->hw.conf.channel;
 	info->band = tx.channel->band;
 
+	/* set up hw_queue value early */
+	if (!(info->flags & IEEE80211_TX_CTL_TX_OFFCHAN) ||
+	    !(local->hw.flags & IEEE80211_HW_QUEUE_CONTROL))
+		info->hw_queue =
+			sdata->vif.hw_queue[skb_get_queue_mapping(skb)];
+
 	if (!invoke_tx_handlers(&tx))
 		result = __ieee80211_tx(local, &tx.skbs, led_len,
 					tx.sta, txpending);
@@ -2173,7 +2193,6 @@ static bool ieee80211_tx_pending_skb(str
 void ieee80211_tx_pending(unsigned long data)
 {
 	struct ieee80211_local *local = (struct ieee80211_local *)data;
-	struct ieee80211_sub_if_data *sdata;
 	unsigned long flags;
 	int i;
 	bool txok;
@@ -2210,8 +2229,7 @@ void ieee80211_tx_pending(unsigned long
 		}
 
 		if (skb_queue_empty(&local->pending[i]))
-			list_for_each_entry_rcu(sdata, &local->interfaces, list)
-				netif_wake_subqueue(sdata->dev, i);
+			ieee80211_propagate_queue_wake(local, i);
 	}
 	spin_unlock_irqrestore(&local->queue_stop_reason_lock, flags);
 
@@ -2713,11 +2731,13 @@ EXPORT_SYMBOL(ieee80211_get_buffered_bc)
 void ieee80211_tx_skb_tid(struct ieee80211_sub_if_data *sdata,
 			  struct sk_buff *skb, int tid)
 {
+	int ac = ieee802_1d_to_ac[tid];
+
 	skb_set_mac_header(skb, 0);
 	skb_set_network_header(skb, 0);
 	skb_set_transport_header(skb, 0);
 
-	skb_set_queue_mapping(skb, ieee802_1d_to_ac[tid]);
+	skb_set_queue_mapping(skb, ac);
 	skb->priority = tid;
 
 	/*
--- a/net/mac80211/agg-tx.c	2012-03-28 10:39:22.000000000 +0200
+++ b/net/mac80211/agg-tx.c	2012-03-28 10:48:27.000000000 +0200
@@ -314,10 +314,11 @@ ieee80211_wake_queue_agg(struct ieee8021
  * requires a call to ieee80211_agg_splice_finish later
  */
 static void __acquires(agg_queue)
-ieee80211_agg_splice_packets(struct ieee80211_local *local,
+ieee80211_agg_splice_packets(struct ieee80211_sub_if_data *sdata,
 			     struct tid_ampdu_tx *tid_tx, u16 tid)
 {
-	int queue = ieee80211_ac_from_tid(tid);
+	struct ieee80211_local *local = sdata->local;
+	int queue = sdata->vif.hw_queue[ieee80211_ac_from_tid(tid)];
 	unsigned long flags;
 
 	ieee80211_stop_queue_agg(local, tid);
@@ -376,7 +377,7 @@ void ieee80211_tx_ba_session_handle_star
 					" tid %d\n", tid);
 #endif
 		spin_lock_bh(&sta->lock);
-		ieee80211_agg_splice_packets(local, tid_tx, tid);
+		ieee80211_agg_splice_packets(sdata, tid_tx, tid);
 		ieee80211_assign_tid_tx(sta, tid, NULL);
 		ieee80211_agg_splice_finish(local, tid);
 		spin_unlock_bh(&sta->lock);
@@ -586,7 +587,7 @@ static void ieee80211_agg_tx_operational
 	 */
 	spin_lock_bh(&sta->lock);
 
-	ieee80211_agg_splice_packets(local, tid_tx, tid);
+	ieee80211_agg_splice_packets(sta->sdata, tid_tx, tid);
 	/*
 	 * Now mark as operational. This will be visible
 	 * in the TX path, and lets it go lock-free in
@@ -778,7 +779,7 @@ void ieee80211_stop_tx_ba_cb(struct ieee
 	 * more.
 	 */
 
-	ieee80211_agg_splice_packets(local, tid_tx, tid);
+	ieee80211_agg_splice_packets(sta->sdata, tid_tx, tid);
 
 	/* future packets must not find the tid_tx struct any more */
 	ieee80211_assign_tid_tx(sta, tid, NULL);
--- a/net/mac80211/cfg.c	2012-03-28 10:39:22.000000000 +0200
+++ b/net/mac80211/cfg.c	2012-03-28 10:48:27.000000000 +0200
@@ -2098,6 +2098,10 @@ static int ieee80211_mgmt_tx(struct wiph
 
 	IEEE80211_SKB_CB(skb)->flags = flags;
 
+	if (flags & IEEE80211_TX_CTL_TX_OFFCHAN)
+		IEEE80211_SKB_CB(skb)->hw_queue =
+			local->hw.offchannel_tx_hw_queue;
+
 	skb->dev = sdata->dev;
 
 	*cookie = (unsigned long) skb;
@@ -2139,6 +2143,8 @@ static int ieee80211_mgmt_tx(struct wiph
 		/* modify cookie to prevent API mismatches */
 		*cookie ^= 2;
 		IEEE80211_SKB_CB(skb)->flags |= IEEE80211_TX_CTL_TX_OFFCHAN;
+		IEEE80211_SKB_CB(skb)->hw_queue =
+			local->hw.offchannel_tx_hw_queue;
 		local->hw_roc_skb = skb;
 		local->hw_roc_skb_for_status = skb;
 		mutex_unlock(&local->mtx);
--- a/net/mac80211/ieee80211_i.h	2012-03-28 10:39:22.000000000 +0200
+++ b/net/mac80211/ieee80211_i.h	2012-03-28 10:40:04.000000000 +0200
@@ -1426,6 +1426,7 @@ void ieee80211_wake_queue_by_reason(stru
 				    enum queue_stop_reason reason);
 void ieee80211_stop_queue_by_reason(struct ieee80211_hw *hw, int queue,
 				    enum queue_stop_reason reason);
+void ieee80211_propagate_queue_wake(struct ieee80211_local *local, int queue);
 void ieee80211_add_pending_skb(struct ieee80211_local *local,
 			       struct sk_buff *skb);
 void ieee80211_add_pending_skbs_fn(struct ieee80211_local *local,
--- a/net/mac80211/main.c	2012-03-28 10:29:08.000000000 +0200
+++ b/net/mac80211/main.c	2012-03-28 10:48:27.000000000 +0200
@@ -594,6 +594,7 @@ struct ieee80211_hw *ieee80211_alloc_hw(
 	local->hw.max_report_rates = 0;
 	local->hw.max_rx_aggregation_subframes = IEEE80211_MAX_AMPDU_BUF;
 	local->hw.max_tx_aggregation_subframes = IEEE80211_MAX_AMPDU_BUF;
+	local->hw.offchannel_tx_hw_queue = IEEE80211_INVAL_HW_QUEUE;
 	local->hw.conf.long_frame_max_tx_count = wiphy->retry_long;
 	local->hw.conf.short_frame_max_tx_count = wiphy->retry_short;
 	local->user_power_level = -1;
@@ -690,6 +691,10 @@ int ieee80211_register_hw(struct ieee802
 		WLAN_CIPHER_SUITE_AES_CMAC
 	};
 
+	if (hw->flags & IEEE80211_HW_QUEUE_CONTROL &&
+	    local->hw.offchannel_tx_hw_queue == IEEE80211_INVAL_HW_QUEUE)
+		return -EINVAL;
+
 	if ((hw->wiphy->wowlan.flags || hw->wiphy->wowlan.n_patterns)
 #ifdef CONFIG_PM
 	    && (!local->ops->suspend || !local->ops->resume)