[PATCH ath-next v3 2/9] wifi: ath11k: enable airtime queue limits

ath11k does not advertise NL80211_EXT_FEATURE_AQL, and every user of AQL in
mac80211 is gated on that bit: the airtime charge in
ieee80211_tx_dequeue(), ieee80211_txq_airtime_check(),
ieee80211_sta_update_pending_airtime(), and the per-station aql file in
debugfs, which is not even created.

That matters here more than it would elsewhere, because AQL is the only
brake. ath11k uses ieee80211_handle_wake_tx_queue(), whose
wake_tx_push_queue() drains a selected txq whole into the driver, and the
check at the top of ieee80211_tx_dequeue() is what stops that drain.
Without the feature bit nothing does, so mac80211 holds no backlog and
every queued byte of a saturated download sits in the hardware TX rings,
where there is no AQM and no flow separation.

Measured on an IPQ8074 AP against one HE 160 MHz station at MCS 11, taken
from that station's own aql file while it received 280 Mbit/s: its BE queue
depth reaches 6356 us of the 12000 us default limit, and 2972 us when the
limit is lowered to 500/1000 us. Pending airtime stands above the limit it
is tested against because ieee80211_txq_airtime_check() admits a frame
while pending is still below it, and the TIDs of one station test it
independently. Without this patch the file does not exist and the limits
are never consulted.

The rate the estimator needs is already there: ath11k keeps a per-station
rate_info in arsta->last_txrate and passes it to ieee80211_tx_status_ext(),
which stores it as tx_stats.last_rate_info, and that is what
ieee80211_calc_expected_tx_airtime() reads. Where no rate is known yet the
estimator falls back to its 4 us floor, so a station's queue is charged the
minimum until the first HTT PPDU stats arrive and the per-AC limits of 5000
and 12000 us stay loose over that window. The current code charges nothing
and consults no limit at all, so nothing is held back that is not held back
today. A rate that has gone stale low overcharges a station that has since
sped up, bounded by the same lag.

The estimate is only as fresh as arsta->last_txrate, which is updated from
the HTT PPDU stats when a descriptor is evicted from ar->ppdu_stats_info,
so the rate behind it can lag a rate change by up to
HTT_PPDU_DESC_MAX_DEPTH PPDUs.

ieee80211_sta_update_pending_airtime() returns the airtime but does not
reschedule the txq, and ath11k has no completion-side push, so a queue held
back by AQL is re-poked only by the next enqueue or queue wake.

The bit alone brakes the queue but does not refill it: the check at the top
of ieee80211_tx_dequeue() stops the drain, and nothing restarts it until
mac80211 next calls the wake_tx_queue callback. Later patches in this
series give the driver a scheduling round and run it from tx completion,
which is what makes a binding limit affordable.

ath10k and mt76 set the same feature bit.

Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.9.0.1-02146-QCAHKSWPL_SILICONZ-1
Assisted-by: Claude:claude-opus-5
Signed-off-by: Julius Bairaktaris <[email protected]>
---
 drivers/net/wireless/ath/ath11k/mac.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/wireless/ath/ath11k/mac.c b/drivers/net/wireless/ath/ath11k/mac.c
index 2d55cdc4d165..38f641bbc53c 100644
--- a/drivers/net/wireless/ath/ath11k/mac.c
+++ b/drivers/net/wireless/ath/ath11k/mac.c
@@ -10592,6 +10592,7 @@ static int __ath11k_mac_register(struct ath11k *ar)
 	ar->hw->sta_data_size = sizeof(struct ath11k_sta);
 
 	wiphy_ext_feature_set(ar->hw->wiphy, NL80211_EXT_FEATURE_CQM_RSSI_LIST);
+	wiphy_ext_feature_set(ar->hw->wiphy, NL80211_EXT_FEATURE_AQL);
 	wiphy_ext_feature_set(ar->hw->wiphy, NL80211_EXT_FEATURE_STA_TX_PWR);
 	if (test_bit(WMI_TLV_SERVICE_BSS_COLOR_OFFLOAD,
 		     ar->ab->wmi_ab.svc_map)) {
-- 
2.53.0