rtl8xxxu: Improve TX performance of RTL8723BU on rtl8xxxu driver

We have 3 laptops which connect the wifi by the same RTL8723BU.
The PCI VID/PID of the wifi chip is 10EC:B720 which is supported.
They have the same problem with the in-kernel rtl8xxxu driver, the
iperf (as a client to an ethernet-connected server) gets ~1Mbps.
Nevertheless, the signal strength is reported as around -40dBm,
which is quite good. From the wireshark capture, the tx rate for each
data and qos data packet is only 1Mbps. Compare to the Realtek driver
at https://github.com/lwfinger/rtl8723bu, the same iperf test gets
~12Mbps or better. The signal strength is reported similarly around
-40dBm. That's why we want to improve.

After reading the source code of the rtl8xxxu driver and Realtek's, the
major difference is that Realtek's driver has a watchdog which will keep
monitoring the signal quality and updating the rate mask just like the
rtl8xxxu_gen2_update_rate_mask() does if signal quality changes.
And this kind of watchdog also exists in rtlwifi driver of some specific
chips, ex rtl8192ee, rtl8188ee, rtl8723ae, rtl8821ae...etc. They have
the same member function named dm_watchdog and will invoke the
corresponding dm_refresh_rate_adaptive_mask to adjust the tx rate
mask.

With this commit, the tx rate of each data and qos data packet will
be 39Mbps (MCS4) with the 0xF00000 as the tx rate mask. The 20th bit
to 23th bit means MCS4 to MCS7. It means that the firmware still picks
the lowest rate from the rate mask and explains why the tx rate of
data and qos data is always lowest 1Mbps because the default rate mask
passed is always 0xFFFFFFF ranges from the basic CCK rate, OFDM rate,
and MCS rate. However, with Realtek's driver, the tx rate observed from
wireshark under the same condition is almost 65Mbps or 72Mbps, which
indicating that rtl8xxxu could still be further improved.
Signed-off-by: Chris Chiu <chiu@endlessm.com>
Reviewed-by: Daniel Drake <drake@endlessm.com>
Acked-by: Jes Sorensen <Jes.Sorensen@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

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

@@ -1187,6 +1187,48 @@ struct rtl8723bu_c2h {
 
 struct rtl8xxxu_fileops;
 
+/*mlme related.*/
+enum wireless_mode {
+	WIRELESS_MODE_UNKNOWN = 0,
+	/* Sub-Element */
+	WIRELESS_MODE_B = BIT(0),
+	WIRELESS_MODE_G = BIT(1),
+	WIRELESS_MODE_A = BIT(2),
+	WIRELESS_MODE_N_24G = BIT(3),
+	WIRELESS_MODE_N_5G = BIT(4),
+	WIRELESS_AUTO = BIT(5),
+	WIRELESS_MODE_AC = BIT(6),
+	WIRELESS_MODE_MAX = 0x7F,
+};
+
+/* from rtlwifi/wifi.h */
+enum ratr_table_mode_new {
+	RATEID_IDX_BGN_40M_2SS = 0,
+	RATEID_IDX_BGN_40M_1SS = 1,
+	RATEID_IDX_BGN_20M_2SS_BN = 2,
+	RATEID_IDX_BGN_20M_1SS_BN = 3,
+	RATEID_IDX_GN_N2SS = 4,
+	RATEID_IDX_GN_N1SS = 5,
+	RATEID_IDX_BG = 6,
+	RATEID_IDX_G = 7,
+	RATEID_IDX_B = 8,
+	RATEID_IDX_VHT_2SS = 9,
+	RATEID_IDX_VHT_1SS = 10,
+	RATEID_IDX_MIX1 = 11,
+	RATEID_IDX_MIX2 = 12,
+	RATEID_IDX_VHT_3SS = 13,
+	RATEID_IDX_BGN_3SS = 14,
+};
+
+#define RTL8XXXU_RATR_STA_INIT 0
+#define RTL8XXXU_RATR_STA_HIGH 1
+#define RTL8XXXU_RATR_STA_MID  2
+#define RTL8XXXU_RATR_STA_LOW  3
+
+#define RTL8XXXU_NOISE_FLOOR_MIN	-100
+#define RTL8XXXU_SNR_THRESH_HIGH	50
+#define RTL8XXXU_SNR_THRESH_LOW	20
+
 struct rtl8xxxu_priv {
 	struct ieee80211_hw *hw;
 	struct usb_device *udev;
@@ -1291,6 +1333,13 @@ struct rtl8xxxu_priv {
 	u8 pi_enabled:1;
 	u8 no_pape:1;
 	u8 int_buf[USB_INTR_CONTENT_LENGTH];
+	u8 rssi_level;
+	/*
+	 * Only one virtual interface permitted because only STA mode
+	 * is supported and no iface_combinations are provided.
+	 */
+	struct ieee80211_vif *vif;
+	struct delayed_work ra_watchdog;
 };
 
 struct rtl8xxxu_rx_urb {
@@ -1326,7 +1375,7 @@ struct rtl8xxxu_fileops {
 	void (*set_tx_power) (struct rtl8xxxu_priv *priv, int channel,
 			      bool ht40);
 	void (*update_rate_mask) (struct rtl8xxxu_priv *priv,
-				  u32 ramask, int sgi);
+				  u32 ramask, u8 rateid, int sgi);
 	void (*report_connect) (struct rtl8xxxu_priv *priv,
 				u8 macid, bool connect);
 	void (*fill_txdesc) (struct ieee80211_hw *hw, struct ieee80211_hdr *hdr,
@@ -1411,9 +1460,9 @@ void rtl8xxxu_gen2_config_channel(struct ieee80211_hw *hw);
 void rtl8xxxu_gen1_usb_quirks(struct rtl8xxxu_priv *priv);
 void rtl8xxxu_gen2_usb_quirks(struct rtl8xxxu_priv *priv);
 void rtl8xxxu_update_rate_mask(struct rtl8xxxu_priv *priv,
-			       u32 ramask, int sgi);
+			       u32 ramask, u8 rateid, int sgi);
 void rtl8xxxu_gen2_update_rate_mask(struct rtl8xxxu_priv *priv,
-				    u32 ramask, int sgi);
+				    u32 ramask, u8 rateid, int sgi);
 void rtl8xxxu_gen1_report_connect(struct rtl8xxxu_priv *priv,
 				  u8 macid, bool connect);
 void rtl8xxxu_gen2_report_connect(struct rtl8xxxu_priv *priv,

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

@@ -4304,7 +4304,8 @@ static void rtl8xxxu_sw_scan_complete(struct ieee80211_hw *hw,
 	rtl8xxxu_write8(priv, REG_BEACON_CTRL, val8);
 }
 
-void rtl8xxxu_update_rate_mask(struct rtl8xxxu_priv *priv, u32 ramask, int sgi)
+void rtl8xxxu_update_rate_mask(struct rtl8xxxu_priv *priv,
+			       u32 ramask, u8 rateid, int sgi)
 {
 	struct h2c_cmd h2c;
 
@@ -4324,7 +4325,7 @@ void rtl8xxxu_update_rate_mask(struct rtl8xxxu_priv *priv, u32 ramask, int sgi)
 }
 
 void rtl8xxxu_gen2_update_rate_mask(struct rtl8xxxu_priv *priv,
-				    u32 ramask, int sgi)
+				    u32 ramask, u8 rateid, int sgi)
 {
 	struct h2c_cmd h2c;
 	u8 bw = 0;
@@ -4338,7 +4339,7 @@ void rtl8xxxu_gen2_update_rate_mask(struct rtl8xxxu_priv *priv,
 	h2c.b_macid_cfg.ramask3 = (ramask >> 24) & 0xff;
 
 	h2c.ramask.arg = 0x80;
-	h2c.b_macid_cfg.data1 = 0;
+	h2c.b_macid_cfg.data1 = rateid;
 	if (sgi)
 		h2c.b_macid_cfg.data1 |= BIT(7);
 
@@ -4478,6 +4479,40 @@ static void rtl8xxxu_set_basic_rates(struct rtl8xxxu_priv *priv, u32 rate_cfg)
 	rtl8xxxu_write8(priv, REG_INIRTS_RATE_SEL, rate_idx);
 }
 
+static u16
+rtl8xxxu_wireless_mode(struct ieee80211_hw *hw, struct ieee80211_sta *sta)
+{
+	u16 network_type = WIRELESS_MODE_UNKNOWN;
+	u32 rate_mask;
+
+	rate_mask = (sta->supp_rates[0] & 0xfff) |
+		    (sta->ht_cap.mcs.rx_mask[0] << 12) |
+		    (sta->ht_cap.mcs.rx_mask[0] << 20);
+
+	if (hw->conf.chandef.chan->band == NL80211_BAND_5GHZ) {
+		if (sta->vht_cap.vht_supported)
+			network_type = WIRELESS_MODE_AC;
+		else if (sta->ht_cap.ht_supported)
+			network_type = WIRELESS_MODE_N_5G;
+
+		network_type |= WIRELESS_MODE_A;
+	} else {
+		if (sta->vht_cap.vht_supported)
+			network_type = WIRELESS_MODE_AC;
+		else if (sta->ht_cap.ht_supported)
+			network_type = WIRELESS_MODE_N_24G;
+
+		if (sta->supp_rates[0] <= 0xf)
+			network_type |= WIRELESS_MODE_B;
+		else if (sta->supp_rates[0] & 0xf)
+			network_type |= (WIRELESS_MODE_B | WIRELESS_MODE_G);
+		else
+			network_type |= WIRELESS_MODE_G;
+	}
+
+	return network_type;
+}
+
 static void
 rtl8xxxu_bss_info_changed(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 			  struct ieee80211_bss_conf *bss_conf, u32 changed)
@@ -4520,7 +4555,10 @@ rtl8xxxu_bss_info_changed(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 				sgi = 1;
 			rcu_read_unlock();
 
-			priv->fops->update_rate_mask(priv, ramask, sgi);
+			priv->vif = vif;
+			priv->rssi_level = RTL8XXXU_RATR_STA_INIT;
+
+			priv->fops->update_rate_mask(priv, ramask, 0, sgi);
 
 			rtl8xxxu_write8(priv, REG_BCN_MAX_ERR, 0xff);
 
@@ -5465,6 +5503,10 @@ static int rtl8xxxu_add_interface(struct ieee80211_hw *hw,
 
 	switch (vif->type) {
 	case NL80211_IFTYPE_STATION:
+		if (!priv->vif)
+			priv->vif = vif;
+		else
+			return -EOPNOTSUPP;
 		rtl8xxxu_stop_tx_beacon(priv);
 
 		val8 = rtl8xxxu_read8(priv, REG_BEACON_CTRL);
@@ -5488,6 +5530,9 @@ static void rtl8xxxu_remove_interface(struct ieee80211_hw *hw,
 	struct rtl8xxxu_priv *priv = hw->priv;
 
 	dev_dbg(&priv->udev->dev, "%s\n", __func__);
+
+	if (priv->vif)
+		priv->vif = NULL;
 }
 
 static int rtl8xxxu_config(struct ieee80211_hw *hw, u32 changed)
@@ -5773,6 +5818,178 @@ rtl8xxxu_ampdu_action(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 	return 0;
 }
 
+static u8 rtl8xxxu_signal_to_snr(int signal)
+{
+	if (signal < RTL8XXXU_NOISE_FLOOR_MIN)
+		signal = RTL8XXXU_NOISE_FLOOR_MIN;
+	else if (signal > 0)
+		signal = 0;
+	return (u8)(signal - RTL8XXXU_NOISE_FLOOR_MIN);
+}
+
+static void rtl8xxxu_refresh_rate_mask(struct rtl8xxxu_priv *priv,
+				       int signal, struct ieee80211_sta *sta)
+{
+	struct ieee80211_hw *hw = priv->hw;
+	u16 wireless_mode;
+	u8 rssi_level, ratr_idx;
+	u8 txbw_40mhz;
+	u8 snr, snr_thresh_high, snr_thresh_low;
+	u8 go_up_gap = 5;
+
+	rssi_level = priv->rssi_level;
+	snr = rtl8xxxu_signal_to_snr(signal);
+	snr_thresh_high = RTL8XXXU_SNR_THRESH_HIGH;
+	snr_thresh_low = RTL8XXXU_SNR_THRESH_LOW;
+	txbw_40mhz = (hw->conf.chandef.width == NL80211_CHAN_WIDTH_40) ? 1 : 0;
+
+	switch (rssi_level) {
+	case RTL8XXXU_RATR_STA_MID:
+		snr_thresh_high += go_up_gap;
+		break;
+	case RTL8XXXU_RATR_STA_LOW:
+		snr_thresh_high += go_up_gap;
+		snr_thresh_low += go_up_gap;
+		break;
+	default:
+		break;
+	}
+
+	if (snr > snr_thresh_high)
+		rssi_level = RTL8XXXU_RATR_STA_HIGH;
+	else if (snr > snr_thresh_low)
+		rssi_level = RTL8XXXU_RATR_STA_MID;
+	else
+		rssi_level = RTL8XXXU_RATR_STA_LOW;
+
+	if (rssi_level != priv->rssi_level) {
+		int sgi = 0;
+		u32 rate_bitmap = 0;
+
+		rcu_read_lock();
+		rate_bitmap = (sta->supp_rates[0] & 0xfff) |
+				(sta->ht_cap.mcs.rx_mask[0] << 12) |
+				(sta->ht_cap.mcs.rx_mask[1] << 20);
+		if (sta->ht_cap.cap &
+		    (IEEE80211_HT_CAP_SGI_40 | IEEE80211_HT_CAP_SGI_20))
+			sgi = 1;
+		rcu_read_unlock();
+
+		wireless_mode = rtl8xxxu_wireless_mode(hw, sta);
+		switch (wireless_mode) {
+		case WIRELESS_MODE_B:
+			ratr_idx = RATEID_IDX_B;
+			if (rate_bitmap & 0x0000000c)
+				rate_bitmap &= 0x0000000d;
+			else
+				rate_bitmap &= 0x0000000f;
+			break;
+		case WIRELESS_MODE_A:
+		case WIRELESS_MODE_G:
+			ratr_idx = RATEID_IDX_G;
+			if (rssi_level == RTL8XXXU_RATR_STA_HIGH)
+				rate_bitmap &= 0x00000f00;
+			else
+				rate_bitmap &= 0x00000ff0;
+			break;
+		case (WIRELESS_MODE_B | WIRELESS_MODE_G):
+			ratr_idx = RATEID_IDX_BG;
+			if (rssi_level == RTL8XXXU_RATR_STA_HIGH)
+				rate_bitmap &= 0x00000f00;
+			else if (rssi_level == RTL8XXXU_RATR_STA_MID)
+				rate_bitmap &= 0x00000ff0;
+			else
+				rate_bitmap &= 0x00000ff5;
+			break;
+		case WIRELESS_MODE_N_24G:
+		case WIRELESS_MODE_N_5G:
+		case (WIRELESS_MODE_G | WIRELESS_MODE_N_24G):
+		case (WIRELESS_MODE_A | WIRELESS_MODE_N_5G):
+			if (priv->tx_paths == 2 && priv->rx_paths == 2)
+				ratr_idx = RATEID_IDX_GN_N2SS;
+			else
+				ratr_idx = RATEID_IDX_GN_N1SS;
+			break;
+		case (WIRELESS_MODE_B | WIRELESS_MODE_G | WIRELESS_MODE_N_24G):
+		case (WIRELESS_MODE_B | WIRELESS_MODE_N_24G):
+			if (txbw_40mhz) {
+				if (priv->tx_paths == 2 && priv->rx_paths == 2)
+					ratr_idx = RATEID_IDX_BGN_40M_2SS;
+				else
+					ratr_idx = RATEID_IDX_BGN_40M_1SS;
+			} else {
+				if (priv->tx_paths == 2 && priv->rx_paths == 2)
+					ratr_idx = RATEID_IDX_BGN_20M_2SS_BN;
+				else
+					ratr_idx = RATEID_IDX_BGN_20M_1SS_BN;
+			}
+
+			if (priv->tx_paths == 2 && priv->rx_paths == 2) {
+				if (rssi_level == RTL8XXXU_RATR_STA_HIGH) {
+					rate_bitmap &= 0x0f8f0000;
+				} else if (rssi_level == RTL8XXXU_RATR_STA_MID) {
+					rate_bitmap &= 0x0f8ff000;
+				} else {
+					if (txbw_40mhz)
+						rate_bitmap &= 0x0f8ff015;
+					else
+						rate_bitmap &= 0x0f8ff005;
+				}
+			} else {
+				if (rssi_level == RTL8XXXU_RATR_STA_HIGH) {
+					rate_bitmap &= 0x000f0000;
+				} else if (rssi_level == RTL8XXXU_RATR_STA_MID) {
+					rate_bitmap &= 0x000ff000;
+				} else {
+					if (txbw_40mhz)
+						rate_bitmap &= 0x000ff015;
+					else
+						rate_bitmap &= 0x000ff005;
+				}
+			}
+			break;
+		default:
+			ratr_idx = RATEID_IDX_BGN_40M_2SS;
+			rate_bitmap &= 0x0fffffff;
+			break;
+		}
+
+		priv->rssi_level = rssi_level;
+		priv->fops->update_rate_mask(priv, rate_bitmap, ratr_idx, sgi);
+	}
+}
+
+static void rtl8xxxu_watchdog_callback(struct work_struct *work)
+{
+	struct ieee80211_vif *vif;
+	struct rtl8xxxu_priv *priv;
+
+	priv = container_of(work, struct rtl8xxxu_priv, ra_watchdog.work);
+	vif = priv->vif;
+
+	if (vif && vif->type == NL80211_IFTYPE_STATION) {
+		int signal;
+		struct ieee80211_sta *sta;
+
+		rcu_read_lock();
+		sta = ieee80211_find_sta(vif, vif->bss_conf.bssid);
+		if (!sta) {
+			struct device *dev = &priv->udev->dev;
+
+			dev_dbg(dev, "%s: no sta found\n", __func__);
+			rcu_read_unlock();
+			goto out;
+		}
+		rcu_read_unlock();
+
+		signal = ieee80211_ave_rssi(vif);
+		rtl8xxxu_refresh_rate_mask(priv, signal, sta);
+	}
+
+out:
+	schedule_delayed_work(&priv->ra_watchdog, 2 * HZ);
+}
+
 static int rtl8xxxu_start(struct ieee80211_hw *hw)
 {
 	struct rtl8xxxu_priv *priv = hw->priv;
@@ -5829,6 +6046,8 @@ static int rtl8xxxu_start(struct ieee80211_hw *hw)
 
 		ret = rtl8xxxu_submit_rx_urb(priv, rx_urb);
 	}
+
+	schedule_delayed_work(&priv->ra_watchdog, 2 * HZ);
 exit:
 	/*
 	 * Accept all data and mgmt frames
@@ -5880,6 +6099,8 @@ static void rtl8xxxu_stop(struct ieee80211_hw *hw)
 	if (priv->usb_interrupts)
 		rtl8xxxu_write32(priv, REG_USB_HIMR, 0);
 
+	cancel_delayed_work_sync(&priv->ra_watchdog);
+
 	rtl8xxxu_free_rx_resources(priv);
 	rtl8xxxu_free_tx_resources(priv);
 }
@@ -6052,6 +6273,7 @@ static int rtl8xxxu_probe(struct usb_interface *interface,
 	INIT_LIST_HEAD(&priv->rx_urb_pending_list);
 	spin_lock_init(&priv->rx_urb_lock);
 	INIT_WORK(&priv->rx_urb_wq, rtl8xxxu_rx_urb_work);
+	INIT_DELAYED_WORK(&priv->ra_watchdog, rtl8xxxu_watchdog_callback);
 
 	usb_set_intfdata(interface, hw);