mac80211: async station powersave handling

Some devices require that all frames to a station
are flushed when that station goes into powersave
mode before being able to send frames to that
station again when it wakes up or polls -- all in
order to avoid reordering and too many or too few
frames being sent to the station when it polls.

Normally, this is the case unless the station
goes to sleep and wakes up very quickly again.
But in that case, frames for it may be pending
on the hardware queues, and thus races could
happen in the case of multiple hardware queues
used for QoS/WMM. Normally this isn't a problem,
but with the iwlwifi mechanism we need to make
sure the race doesn't happen.

This makes mac80211 able to cope with the race
with driver help by a new WLAN_STA_PS_DRIVER
per-station flag that can be controlled by the
driver and tells mac80211 whether it can transmit
frames or not. This flag must be set according to
very specific rules outlined in the documentation
for the function that controls it.

When we buffer new frames for the station, we
normally set the TIM bit right away, but while
the driver has blocked transmission to that sta
we need to avoid that as well since we cannot
respond to the station if it wakes up due to the
TIM bit. Once the driver unblocks, we can set
the TIM bit.

Similarly, when the station just wakes up, we
need to wait until all other frames are flushed
before we can transmit frames to that station,
so the same applies here, we need to wait for
the driver to give the OK.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 117 insertions, 1 deletions

diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index cde2da7a74d..be59456e8a4 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -171,6 +171,8 @@ void sta_info_destroy(struct sta_info *sta)
 
 	local = sta->local;
 
+	cancel_work_sync(&sta->drv_unblock_wk);
+
 	rate_control_remove_sta_debugfs(sta);
 	ieee80211_sta_debugfs_remove(sta);
 
@@ -259,6 +261,21 @@ static void sta_info_hash_add(struct ieee80211_local *local,
 	rcu_assign_pointer(local->sta_hash[STA_HASH(sta->sta.addr)], sta);
 }
 
+static void sta_unblock(struct work_struct *wk)
+{
+	struct sta_info *sta;
+
+	sta = container_of(wk, struct sta_info, drv_unblock_wk);
+
+	if (sta->dead)
+		return;
+
+	if (!test_sta_flags(sta, WLAN_STA_PS_STA))
+		ieee80211_sta_ps_deliver_wakeup(sta);
+	else if (test_and_clear_sta_flags(sta, WLAN_STA_PSPOLL))
+		ieee80211_sta_ps_deliver_poll_response(sta);
+}
+
 struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
 				u8 *addr, gfp_t gfp)
 {
@@ -272,6 +289,7 @@ struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
 
 	spin_lock_init(&sta->lock);
 	spin_lock_init(&sta->flaglock);
+	INIT_WORK(&sta->drv_unblock_wk, sta_unblock);
 
 	memcpy(sta->sta.addr, addr, ETH_ALEN);
 	sta->local = local;
@@ -478,8 +496,10 @@ static void __sta_info_unlink(struct sta_info **sta)
 	}
 
 	list_del(&(*sta)->list);
+	(*sta)->dead = true;
 
-	if (test_and_clear_sta_flags(*sta, WLAN_STA_PS)) {
+	if (test_and_clear_sta_flags(*sta,
+				WLAN_STA_PS_STA | WLAN_STA_PS_DRIVER)) {
 		BUG_ON(!sdata->bss);
 
 		atomic_dec(&sdata->bss->num_sta_ps);
@@ -825,3 +845,99 @@ struct ieee80211_sta *ieee80211_find_sta(struct ieee80211_vif *vif,
 	return ieee80211_find_sta_by_hw(&sdata->local->hw, addr);
 }
 EXPORT_SYMBOL(ieee80211_find_sta);
+
+/* powersave support code */
+void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
+{
+	struct ieee80211_sub_if_data *sdata = sta->sdata;
+	struct ieee80211_local *local = sdata->local;
+	int sent, buffered;
+
+	drv_sta_notify(local, &sdata->vif, STA_NOTIFY_AWAKE, &sta->sta);
+
+	if (!skb_queue_empty(&sta->ps_tx_buf))
+		sta_info_clear_tim_bit(sta);
+
+	/* Send all buffered frames to the station */
+	sent = ieee80211_add_pending_skbs(local, &sta->tx_filtered);
+	buffered = ieee80211_add_pending_skbs(local, &sta->ps_tx_buf);
+	sent += buffered;
+	local->total_ps_buffered -= buffered;
+
+#ifdef CONFIG_MAC80211_VERBOSE_PS_DEBUG
+	printk(KERN_DEBUG "%s: STA %pM aid %d sending %d filtered/%d PS frames "
+	       "since STA not sleeping anymore\n", sdata->dev->name,
+	       sta->sta.addr, sta->sta.aid, sent - buffered, buffered);
+#endif /* CONFIG_MAC80211_VERBOSE_PS_DEBUG */
+}
+
+void ieee80211_sta_ps_deliver_poll_response(struct sta_info *sta)
+{
+	struct ieee80211_sub_if_data *sdata = sta->sdata;
+	struct ieee80211_local *local = sdata->local;
+	struct sk_buff *skb;
+	int no_pending_pkts;
+
+	skb = skb_dequeue(&sta->tx_filtered);
+	if (!skb) {
+		skb = skb_dequeue(&sta->ps_tx_buf);
+		if (skb)
+			local->total_ps_buffered--;
+	}
+	no_pending_pkts = skb_queue_empty(&sta->tx_filtered) &&
+		skb_queue_empty(&sta->ps_tx_buf);
+
+	if (skb) {
+		struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+		struct ieee80211_hdr *hdr =
+			(struct ieee80211_hdr *) skb->data;
+
+		/*
+		 * Tell TX path to send this frame even though the STA may
+		 * still remain is PS mode after this frame exchange.
+		 */
+		info->flags |= IEEE80211_TX_CTL_PSPOLL_RESPONSE;
+
+#ifdef CONFIG_MAC80211_VERBOSE_PS_DEBUG
+		printk(KERN_DEBUG "STA %pM aid %d: PS Poll (entries after %d)\n",
+		       sta->sta.addr, sta->sta.aid,
+		       skb_queue_len(&sta->ps_tx_buf));
+#endif /* CONFIG_MAC80211_VERBOSE_PS_DEBUG */
+
+		/* Use MoreData flag to indicate whether there are more
+		 * buffered frames for this STA */
+		if (no_pending_pkts)
+			hdr->frame_control &= cpu_to_le16(~IEEE80211_FCTL_MOREDATA);
+		else
+			hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_MOREDATA);
+
+		ieee80211_add_pending_skb(local, skb);
+
+		if (no_pending_pkts)
+			sta_info_clear_tim_bit(sta);
+#ifdef CONFIG_MAC80211_VERBOSE_PS_DEBUG
+	} else {
+		/*
+		 * FIXME: This can be the result of a race condition between
+		 *	  us expiring a frame and the station polling for it.
+		 *	  Should we send it a null-func frame indicating we
+		 *	  have nothing buffered for it?
+		 */
+		printk(KERN_DEBUG "%s: STA %pM sent PS Poll even "
+		       "though there are no buffered frames for it\n",
+		       sdata->dev->name, sta->sta.addr);
+#endif /* CONFIG_MAC80211_VERBOSE_PS_DEBUG */
+	}
+}
+
+void ieee80211_sta_block_awake(struct ieee80211_hw *hw,
+			       struct ieee80211_sta *pubsta, bool block)
+{
+	struct sta_info *sta = container_of(pubsta, struct sta_info, sta);
+
+	if (block)
+		set_sta_flags(sta, WLAN_STA_PS_DRIVER);
+	else
+		ieee80211_queue_work(hw, &sta->drv_unblock_wk);
+}
+EXPORT_SYMBOL(ieee80211_sta_block_awake);