From: Felix Fietkau <nbd@nbd.name>
Date: Sat, 11 Jun 2022 16:34:32 +0200
Subject: [PATCH] mac80211: improve AQL tx time estimation

If airtime cannot be calculated because of missing or unsupported rate info,
use the smallest possible non-zero value for estimated tx time.
This improves handling of these cases by preventing queueing of as many packets
as the driver/hardware queue can hold for these stations.
Also slightly improve limiting queueing by explicitly rounding up small values.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---

--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1107,20 +1107,24 @@ struct ieee80211_tx_info {
 	};
 };
 
+#define IEEE80211_TX_TIME_EST_UNIT 4
+
+static inline u16
+ieee80211_info_get_tx_time_est(struct ieee80211_tx_info *info)
+{
+	return info->tx_time_est * IEEE80211_TX_TIME_EST_UNIT;
+}
+
 static inline u16
 ieee80211_info_set_tx_time_est(struct ieee80211_tx_info *info, u16 tx_time_est)
 {
 	/* We only have 10 bits in tx_time_est, so store airtime
 	 * in increments of 4us and clamp the maximum to 2**12-1
 	 */
-	info->tx_time_est = min_t(u16, tx_time_est, 4095) >> 2;
-	return info->tx_time_est << 2;
-}
+	tx_time_est = DIV_ROUND_UP(tx_time_est, IEEE80211_TX_TIME_EST_UNIT);
+	info->tx_time_est = min_t(u16, tx_time_est, BIT(10) - 1);
 
-static inline u16
-ieee80211_info_get_tx_time_est(struct ieee80211_tx_info *info)
-{
-	return info->tx_time_est << 2;
+	return ieee80211_info_get_tx_time_est(info);
 }
 
 /**
--- a/net/mac80211/status.c
+++ b/net/mac80211/status.c
@@ -999,6 +999,8 @@ static void __ieee80211_tx_status(struct
 								   NULL,
 								   skb->len,
 								   false);
+			if (!airtime)
+				airtime = IEEE80211_TX_TIME_EST_UNIT;
 
 			ieee80211_register_airtime(txq, airtime, 0);
 		}
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -3798,13 +3798,12 @@ encap_out:
 
 		airtime = ieee80211_calc_expected_tx_airtime(hw, vif, txq->sta,
 							     skb->len, ampdu);
-		if (airtime) {
-			airtime = ieee80211_info_set_tx_time_est(info, airtime);
-			ieee80211_sta_update_pending_airtime(local, tx.sta,
-							     txq->ac,
-							     airtime,
-							     false);
-		}
+		if (!airtime)
+			airtime = IEEE80211_TX_TIME_EST_UNIT;
+
+		airtime = ieee80211_info_set_tx_time_est(info, airtime);
+		ieee80211_sta_update_pending_airtime(local, tx.sta, txq->ac,
+						     airtime, false);
 	}
 
 	return skb;