linux-kernel - [PATCH] rtl8xxxu: Improve the A-MPDU retransmission rate with RTS/CTS protection

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Message-Id: <20211129143953.369557-1-chris.chiu@canonical.com>
Date:   Mon, 29 Nov 2021 22:39:53 +0800
From:   Chris Chiu <chris.chiu@...onical.com>
To:     Jes.Sorensen@...il.com, kvalo@...eaurora.org, davem@...emloft.net,
        kuba@...nel.org
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Chris Chiu <chris.chiu@...onical.com>
Subject: [PATCH] rtl8xxxu: Improve the A-MPDU retransmission rate with RTS/CTS protection

The A-MPDU retransmission rate is always high (> 20%) even in a very
clean environment. However, the vendor driver retransimission rate is
< 10% in the same test bed. The different is the vendor driver starts
the A-MPDU TXOP with initial RTS/CTS handshake which is observed in the
air capture and the TX descriptor. Since there's no related field in
TX descriptor to enable the L-SIG TXOP protection and the duration,
applying the RTS/CTS protection instead helps to lower the retransmission
rate from > 20% to ~12% in the same test setup.

Signed-off-by: Chris Chiu <chris.chiu@...onical.com>
---
 drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c b/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c
index a42e2081b75f..06d59ffb7444 100644
--- a/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c
+++ b/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c
@@ -4859,7 +4859,7 @@ rtl8xxxu_fill_txdesc_v1(struct ieee80211_hw *hw, struct ieee80211_hdr *hdr,
 	 * rts_rate is zero if RTS/CTS or CTS to SELF are not enabled
 	 */
 	tx_desc->txdw4 |= cpu_to_le32(rts_rate << TXDESC32_RTS_RATE_SHIFT);
-	if (rate_flags & IEEE80211_TX_RC_USE_RTS_CTS) {
+	if (ampdu_enable || (rate_flags & IEEE80211_TX_RC_USE_RTS_CTS)) {
 		tx_desc->txdw4 |= cpu_to_le32(TXDESC32_RTS_CTS_ENABLE);
 		tx_desc->txdw4 |= cpu_to_le32(TXDESC32_HW_RTS_ENABLE);
 	} else if (rate_flags & IEEE80211_TX_RC_USE_CTS_PROTECT) {
@@ -4930,7 +4930,7 @@ rtl8xxxu_fill_txdesc_v2(struct ieee80211_hw *hw, struct ieee80211_hdr *hdr,
 	/*
 	 * rts_rate is zero if RTS/CTS or CTS to SELF are not enabled
 	 */
-	if (rate_flags & IEEE80211_TX_RC_USE_RTS_CTS) {
+	if (ampdu_enable || (rate_flags & IEEE80211_TX_RC_USE_RTS_CTS)) {
 		tx_desc40->txdw3 |= cpu_to_le32(TXDESC40_RTS_CTS_ENABLE);
 		tx_desc40->txdw3 |= cpu_to_le32(TXDESC40_HW_RTS_ENABLE);
 	} else if (rate_flags & IEEE80211_TX_RC_USE_CTS_PROTECT) {
-- 
2.25.1