rtl8xxxu: Use lower tx rates for the ack packet

According to the Realtek propritary driver and the rtw88 driver, the
tx rates of the ack (includes block ack) are initialized with lower
tx rates (no HT rates) which is set by the RRSR register value. In
real cases, ack rate higher than current tx rate could lead to
difficulty for the receiving end to receive management/control frames.
The retransmission rate would be higher then expected when the driver
is acting as receiver and the RSSI is not good.

Cross out higer rates for ack packet before implementing dynamic rrsr
configuration like the commit 48308726 ("rtw88: add dynamic rrsr
configuration").
Signed-off-by: Chris Chiu <chris.chiu@canonical.com>
Acked-by: Jes Sorensen <Jes.Sorensen@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211001040044.1028708-1-chris.chiu@canonical.com

drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c

@@ -4460,13 +4460,17 @@ void rtl8xxxu_gen1_init_aggregation(struct rtl8xxxu_priv *priv)
 
 static void rtl8xxxu_set_basic_rates(struct rtl8xxxu_priv *priv, u32 rate_cfg)
 {
+	struct ieee80211_hw *hw = priv->hw;
 	u32 val32;
 	u8 rate_idx = 0;
 
 	rate_cfg &= RESPONSE_RATE_BITMAP_ALL;
 
 	val32 = rtl8xxxu_read32(priv, REG_RESPONSE_RATE_SET);
-	val32 &= ~RESPONSE_RATE_BITMAP_ALL;
+	if (hw->conf.chandef.chan->band == NL80211_BAND_5GHZ)
+		val32 &= RESPONSE_RATE_RRSR_INIT_5G;
+	else
+		val32 &= RESPONSE_RATE_RRSR_INIT_2G;
 	val32 |= rate_cfg;
 	rtl8xxxu_write32(priv, REG_RESPONSE_RATE_SET, val32);
 

drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_regs.h

@@ -516,6 +516,8 @@
 #define REG_RESPONSE_RATE_SET		0x0440
 #define  RESPONSE_RATE_BITMAP_ALL	0xfffff
 #define  RESPONSE_RATE_RRSR_CCK_ONLY_1M	0xffff1
+#define  RESPONSE_RATE_RRSR_INIT_2G	0x15f
+#define  RESPONSE_RATE_RRSR_INIT_5G	0x150
 #define  RSR_1M				BIT(0)
 #define  RSR_2M				BIT(1)
 #define  RSR_5_5M			BIT(2)