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, 9 insertions, 4 deletions

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index c7dc8ccff5b2..bfaa43e096d2 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -374,7 +374,7 @@ ieee80211_tx_h_unicast_ps_buf(struct ieee80211_tx_data *tx)
 
 	staflags = get_sta_flags(sta);
 
-	if (unlikely((staflags & WLAN_STA_PS) &&
+	if (unlikely((staflags & (WLAN_STA_PS_STA | WLAN_STA_PS_DRIVER)) &&
 		     !(info->flags & IEEE80211_TX_CTL_PSPOLL_RESPONSE))) {
 #ifdef CONFIG_MAC80211_VERBOSE_PS_DEBUG
 		printk(KERN_DEBUG "STA %pM aid %d: PS buffer (entries "
@@ -397,8 +397,13 @@ ieee80211_tx_h_unicast_ps_buf(struct ieee80211_tx_data *tx)
 		} else
 			tx->local->total_ps_buffered++;
 
-		/* Queue frame to be sent after STA sends an PS Poll frame */
-		if (skb_queue_empty(&sta->ps_tx_buf))
+		/*
+		 * Queue frame to be sent after STA wakes up/polls,
+		 * but don't set the TIM bit if the driver is blocking
+		 * wakeup or poll response transmissions anyway.
+		 */
+		if (skb_queue_empty(&sta->ps_tx_buf) &&
+		    !(staflags & WLAN_STA_PS_DRIVER))
 			sta_info_set_tim_bit(sta);
 
 		info->control.jiffies = jiffies;
@@ -408,7 +413,7 @@ ieee80211_tx_h_unicast_ps_buf(struct ieee80211_tx_data *tx)
 		return TX_QUEUED;
 	}
 #ifdef CONFIG_MAC80211_VERBOSE_PS_DEBUG
-	else if (unlikely(test_sta_flags(sta, WLAN_STA_PS))) {
+	else if (unlikely(staflags & WLAN_STA_PS_STA)) {
 		printk(KERN_DEBUG "%s: STA %pM in PS mode, but pspoll "
 		       "set -> send frame\n", tx->dev->name,
 		       sta->sta.addr);