[PATCH ath-next v4 7/9] wifi: ath11k: charge received airtime to the station deficit

[Julius Bairaktaris]

mac80211's airtime scheduler is configured to account both directions:
local->airtime_flags is AIRTIME_USE_TX | AIRTIME_USE_RX, and
ieee80211_sta_register_airtime() adds the received airtime to the same
deficit the transmit side subtracts from. ath11k passes zero for it, so
an access point serving a station that mostly uploads charges that
station nothing for the medium it occupies, and the deficit that decides
whose queue is served next describes half the traffic.

Register the duration the hardware reports for each received PPDU. It
arrives in the RXPCU PPDU end TLV on the monitor status ring, which is
subscribed for every radio, and ath11k already accumulates it as the
station's rx_duration. Charging it once per PPDU matches what the
transmit side registers, whereas an estimate rebuilt per MSDU counts the
preamble and the interframe space once for every subframe of an
aggregate.

The PPDU end user stats TLV that names the TID is not in the default
monitor status filter, so the airtime is charged to best effort, the
access category the deficit arbitrates the bulk of the traffic in. The
call is made after ab->base_lock is dropped, under the rcu read lock the
loop holds, as the tx completion path does; base_lock is contended by
every tx completion. A PPDU from a peer with no station entry is not
charged to anyone.

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 <julius@xxxxxxxxxxxxxx>
---
 drivers/net/wireless/ath/ath11k/dp_rx.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/net/wireless/ath/ath11k/dp_rx.c b/drivers/net/wireless/ath/ath11k/dp_rx.c
index 68472e1e748a..a7b9bb295728 100644
--- a/drivers/net/wireless/ath/ath11k/dp_rx.c
+++ b/drivers/net/wireless/ath/ath11k/dp_rx.c
@@ -5270,6 +5270,7 @@ int ath11k_dp_rx_process_mon_status(struct ath11k_base *ab, int mac_id,
 	struct sk_buff_head skb_list;
 	struct ath11k_peer *peer;
 	struct ath11k_sta *arsta;
+	struct ieee80211_sta *sta;
 	int num_buffs_reaped = 0;
 	u32 rx_buf_sz;
 	u16 log_type;
@@ -5324,6 +5325,7 @@ int ath11k_dp_rx_process_mon_status(struct ath11k_base *ab, int mac_id,
 			continue;
 		}
 
+		sta = NULL;
 		rcu_read_lock();
 		spin_lock_bh(&ab->base_lock);
 		peer = ath11k_peer_find_by_id(ab, ppdu_info->peer_id);
@@ -5337,12 +5339,25 @@ int ath11k_dp_rx_process_mon_status(struct ath11k_base *ab, int mac_id,
 
 		arsta = ath11k_sta_to_arsta(peer->sta);
 		ath11k_dp_rx_update_peer_stats(arsta, ppdu_info);
+		sta = peer->sta;
 
 		if (ath11k_debugfs_is_pktlog_peer_valid(ar, peer->addr))
 			trace_ath11k_htt_rxdesc(ar, skb->data, log_type, rx_buf_sz);
 
 next_skb:
 		spin_unlock_bh(&ab->base_lock);
+
+		/* The airtime a station spends transmitting is taken from
+		 * the others, so its deficit is charged for it too, with the
+		 * duration the hardware measured for the whole PPDU, as on
+		 * the transmit side. The TLV that names the TID is not in
+		 * the default monitor status filter, so the charge goes to
+		 * BE. Outside base_lock, which tx completion contends for;
+		 * sta is held by the rcu read lock.
+		 */
+		if (sta && ppdu_info->rx_duration)
+			ieee80211_sta_register_airtime(sta, 0, 0,
+						       ppdu_info->rx_duration);
 		rcu_read_unlock();
 
 		dev_kfree_skb_any(skb);
-- 
2.53.0