rtw88: add debugfs to fix tx rate

It is useful to fix the bit rate of TX packets. For example, if
someone is measuring the TX power, or debugging with the issues
of the TX throughput on the field.

To set the value of fixed rate, one should input corresponding
desc rate index (ex, 0x0b for DESC_RATE54M to fix at 54 Mbps).
Set a value larger than DESC_RATE_MAX will disable fix rate, so
the rate adaptive mechanism can resume to work.

Example,
  To fix rate at MCS 1:
  echo 0x0d > /sys/kernel/debug/ieee80211/phy0/rtw88/fix_rate

  To not to fix rate:
  echo 0xff > /sys/kernel/debug/ieee80211/phy0/rtw88/fix_rate

  To know which rate was fixed at:
  cat /sys/kernel/debug/ieee80211/phy0/rtw88/fix_rate
Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20211129020506.6273-1-pkshih@realtek.com

drivers/net/wireless/realtek/rtw88/debug.c

@@ -152,6 +152,22 @@ static int rtw_debugfs_get_rf_read(struct seq_file *m, void *v)
 	return 0;
 }
 
+static int rtw_debugfs_get_fix_rate(struct seq_file *m, void *v)
+{
+	struct rtw_debugfs_priv *debugfs_priv = m->private;
+	struct rtw_dev *rtwdev = debugfs_priv->rtwdev;
+	struct rtw_dm_info *dm_info = &rtwdev->dm_info;
+	u8 fix_rate = dm_info->fix_rate;
+
+	if (fix_rate >= DESC_RATE_MAX) {
+		seq_printf(m, "Fix rate disabled, fix_rate = %u\n", fix_rate);
+		return 0;
+	}
+
+	seq_printf(m, "Data frames fixed at desc rate %u\n", fix_rate);
+	return 0;
+}
+
 static int rtw_debugfs_copy_from_user(char tmp[], int size,
 				      const char __user *buffer, size_t count,
 				      int num)
@@ -437,6 +453,31 @@ static ssize_t rtw_debugfs_set_rf_read(struct file *filp,
 	return count;
 }
 
+static ssize_t rtw_debugfs_set_fix_rate(struct file *filp,
+					const char __user *buffer,
+					size_t count, loff_t *loff)
+{
+	struct seq_file *seqpriv = (struct seq_file *)filp->private_data;
+	struct rtw_debugfs_priv *debugfs_priv = seqpriv->private;
+	struct rtw_dev *rtwdev = debugfs_priv->rtwdev;
+	struct rtw_dm_info *dm_info = &rtwdev->dm_info;
+	u8 fix_rate;
+	char tmp[32 + 1];
+	int ret;
+
+	rtw_debugfs_copy_from_user(tmp, sizeof(tmp), buffer, count, 1);
+
+	ret = kstrtou8(tmp, 0, &fix_rate);
+	if (ret) {
+		rtw_warn(rtwdev, "invalid args, [rate]\n");
+		return ret;
+	}
+
+	dm_info->fix_rate = fix_rate;
+
+	return count;
+}
+
 static int rtw_debug_get_mac_page(struct seq_file *m, void *v)
 {
 	struct rtw_debugfs_priv *debugfs_priv = m->private;
@@ -1094,6 +1135,11 @@ static struct rtw_debugfs_priv rtw_debug_priv_read_reg = {
 	.cb_read = rtw_debugfs_get_read_reg,
 };
 
+static struct rtw_debugfs_priv rtw_debug_priv_fix_rate = {
+	.cb_write = rtw_debugfs_set_fix_rate,
+	.cb_read = rtw_debugfs_get_fix_rate,
+};
+
 static struct rtw_debugfs_priv rtw_debug_priv_dump_cam = {
 	.cb_write = rtw_debugfs_set_single_input,
 	.cb_read = rtw_debugfs_get_dump_cam,
@@ -1164,6 +1210,7 @@ void rtw_debugfs_init(struct rtw_dev *rtwdev)
 	rtw_debugfs_add_rw(read_reg);
 	rtw_debugfs_add_w(rf_write);
 	rtw_debugfs_add_rw(rf_read);
+	rtw_debugfs_add_rw(fix_rate);
 	rtw_debugfs_add_rw(dump_cam);
 	rtw_debugfs_add_rw(rsvd_page);
 	rtw_debugfs_add_r(phy_info);

drivers/net/wireless/realtek/rtw88/main.c

@@ -1862,6 +1862,7 @@ int rtw_core_init(struct rtw_dev *rtwdev)
 
 	rtwdev->sec.total_cam_num = 32;
 	rtwdev->hal.current_channel = 1;
+	rtwdev->dm_info.fix_rate = U8_MAX;
 	set_bit(RTW_BC_MC_MACID, rtwdev->mac_id_map);
 
 	rtw_stats_init(rtwdev);

drivers/net/wireless/realtek/rtw88/main.h

@@ -1631,6 +1631,7 @@ struct rtw_dm_info {
 	u8 cck_gi_u_bnd;
 	u8 cck_gi_l_bnd;
 
+	u8 fix_rate;
 	u8 tx_rate;
 	u32 rrsr_val_init;
 	u32 rrsr_mask_min;

drivers/net/wireless/realtek/rtw88/tx.c

@@ -312,7 +312,9 @@ static void rtw_tx_data_pkt_info_update(struct rtw_dev *rtwdev,
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 	struct ieee80211_hw *hw = rtwdev->hw;
+	struct rtw_dm_info *dm_info = &rtwdev->dm_info;
 	struct rtw_sta_info *si;
+	u8 fix_rate;
 	u16 seq;
 	u8 ampdu_factor = 0;
 	u8 ampdu_density = 0;
@@ -364,6 +366,13 @@ static void rtw_tx_data_pkt_info_update(struct rtw_dev *rtwdev,
 	pkt_info->bw = bw;
 	pkt_info->stbc = stbc;
 	pkt_info->ldpc = ldpc;
+
+	fix_rate = dm_info->fix_rate;
+	if (fix_rate < DESC_RATE_MAX) {
+		pkt_info->rate = fix_rate;
+		pkt_info->dis_rate_fallback = true;
+		pkt_info->use_rate = true;
+	}
 }
 
 void rtw_tx_pkt_info_update(struct rtw_dev *rtwdev,