ath5k: switch to rate table based lookup

Switching from legacy usage of ieee80211_get_tx_rates() lookup to direct
rate table lookup in struct ieee80211_sta->rates.

The current rate control API allows drivers to directly get rates from
ieee80211_sta->rates. ath5k is currently one of the legacy drivers that
perform translation/merge with the internal rate table via
ieee80211_get_tx_rates provided by rate control API.
For our upcoming changes to rate control API and the implementation of
transmit power control, this patch changes the behaviour. The call to
ieee80211_get_tx_rates and subsequent calls are also avoided. ath5k now
directly reads rates from sta->rates into its internal rate table. Cause
ath5k does not rely on the rate array in SKB->CB, this is not considered
anymore except for the first entry (used for probing).

Tested this on a PCEngines ALIX with CMP9-GP miniPCI wifi card (Atheros
AR5213A). Generated traffic between AP and multiple STAs before and
after applying the patch and simultaneously measured throughput and
captured rc_stats. Comparison resulted in same rate selection and no
performance loss between both runs.

Co-developed-by: Thomas Huehn <thomas.huehn@hs-nordhausen.de>
Signed-off-by: Thomas Huehn <thomas.huehn@hs-nordhausen.de>
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20211215215042.637-1-jelonek.jonas@gmail.com

diff --git a/drivers/net/wireless/ath/ath5k/base.c b/drivers/net/wireless/ath/ath5k/base.c
index cef17f3..66d123f 100644 (file)
--- a/drivers/net/wireless/ath/ath5k/base.c
+++ b/drivers/net/wireless/ath/ath5k/base.c
@@ -727,6 +727,43 @@ ath5k_get_rate_hw_value(const struct ieee80211_hw *hw,
        return hw_rate;
 }
 
+static bool ath5k_merge_ratetbl(struct ieee80211_sta *sta,
+                               struct ath5k_buf *bf,
+                               struct ieee80211_tx_info *tx_info)
+{
+       struct ieee80211_sta_rates *ratetbl;
+       u8 i;
+
+       if (!sta)
+               return false;
+
+       ratetbl = rcu_dereference(sta->rates);
+       if (!ratetbl)
+               return false;
+
+       if (tx_info->control.rates[0].idx < 0 ||
+           tx_info->control.rates[0].count == 0)
+       {
+               i = 0;
+       } else {
+               bf->rates[0] = tx_info->control.rates[0];
+               i = 1;
+       }
+
+       for ( ; i < IEEE80211_TX_MAX_RATES; i++) {
+               bf->rates[i].idx = ratetbl->rate[i].idx;
+               bf->rates[i].flags = ratetbl->rate[i].flags;
+               if (tx_info->control.use_rts)
+                       bf->rates[i].count = ratetbl->rate[i].count_rts;
+               else if (tx_info->control.use_cts_prot)
+                       bf->rates[i].count = ratetbl->rate[i].count_cts;
+               else
+                       bf->rates[i].count = ratetbl->rate[i].count;
+       }
+
+       return true;
+}
+
 static int
 ath5k_txbuf_setup(struct ath5k_hw *ah, struct ath5k_buf *bf,
                  struct ath5k_txq *txq, int padsize,
@@ -737,6 +774,7 @@ ath5k_txbuf_setup(struct ath5k_hw *ah, struct ath5k_buf *bf,
        struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
        unsigned int pktlen, flags, keyidx = AR5K_TXKEYIX_INVALID;
        struct ieee80211_rate *rate;
+       struct ieee80211_sta *sta;
        unsigned int mrr_rate[3], mrr_tries[3];
        int i, ret;
        u16 hw_rate;
@@ -753,8 +791,16 @@ ath5k_txbuf_setup(struct ath5k_hw *ah, struct ath5k_buf *bf,
        if (dma_mapping_error(ah->dev, bf->skbaddr))
                return -ENOSPC;
 
-       ieee80211_get_tx_rates(info->control.vif, (control) ? control->sta : NULL, skb, bf->rates,
-                              ARRAY_SIZE(bf->rates));
+       if (control)
+               sta = control->sta;
+       else
+               sta = NULL;
+
+       if (!ath5k_merge_ratetbl(sta, bf, info)) {
+               ieee80211_get_tx_rates(info->control.vif,
+                                      sta, skb, bf->rates,
+                                      ARRAY_SIZE(bf->rates));
+       }
 
        rate = ath5k_get_rate(ah->hw, info, bf, 0);