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Date:   Sun, 23 Oct 2022 00:24:23 +0300
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To:     "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
From:   Bitterblue Smith <rtl8821cerfe2@gmail.com>
Subject: How to use the rate control in mac80211?
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Hi!

What does a driver (rtl8xxxu) need to do to make the rate control work?

I thought it's like this:
1) don't set HAS_RATE_CONTROL
2) tell the chip to use the rate from tx_info->control.rates[0]
3) report if the frame was acked or not

But it's not that easy. I'm always getting MCS0. Currently rtl8xxxu
doesn't ask the chip for TX reports and always sets IEEE80211_TX_STAT_ACK.
I thought this would get me MCS7 for all data frames, but it doesn't.

The rc_stats file from debugfs looks like this after using the connection for a while:

              best    ____________rate__________    ____statistics___    _____last____    ______sum-of________
mode guard #  rate   [name   idx airtime  max_tp]  [avg(tp) avg(prob)]  [retry|suc|att]  [#success | #attempts]
HT20  LGI  1  ABCDPS  MCS0     0    1477     5.6       0.0       0.0       1     0 0             0   0        
HT20  LGI  1       S  MCS1     1     738    10.6       0.0       0.0       0     0 0             0   0        
HT20  LGI  1          MCS2     2     492    14.9       0.0       0.0       0     0 0             0   0        
HT20  LGI  1          MCS3     3     369    18.8       0.0       0.0       0     0 0             0   0        
HT20  LGI  1       S  MCS4     4     246    25.4       0.0       0.0       0     0 0             0   0        
HT20  LGI  1          MCS5     5     185    30.7       0.0       0.0       0     0 0             0   0        
HT20  LGI  1          MCS6     6     164    33.0       0.0       0.0       0     0 0             0   0        
HT20  LGI  1          MCS7     7     148    35.1       0.0       0.0       0     0 0             0   0        
HT20  SGI  1       S  MCS0    64    1329     6.2       0.0       0.0       0     0 0             0   0        
HT20  SGI  1          MCS1    65     665    11.6       0.0       0.0       0     0 0             0   0        
HT20  SGI  1          MCS2    66     443    16.3       0.0       0.0       0     0 0             0   0        
HT20  SGI  1          MCS3    67     332    20.4       0.0       0.0       0     0 0             0   0        
HT20  SGI  1       S  MCS4    68     222    27.2       0.0       0.0       0     0 0             0   0        
HT20  SGI  1          MCS5    69     166    32.8       0.0       0.0       0     0 0             0   0        
HT20  SGI  1          MCS6    70     148    35.1       0.0       0.0       0     0 0             0   0        
HT20  SGI  1          MCS7    71     133    37.3       0.0       0.0       0     0 0             0   0        
HT40  LGI  1       S  MCS0   128     711    10.9       0.0       0.0       0     0 0             0   0        
HT40  LGI  1          MCS1   129     356    19.4       0.0       0.0       0     0 0             0   0        
HT40  LGI  1          MCS2   130     237    26.0       0.0       0.0       0     0 0             0   0        
HT40  LGI  1          MCS3   131     178    31.4       0.0       0.0       0     0 0             0   0        
HT40  LGI  1       S  MCS4   132     119    39.6       0.0       0.0       0     0 0             0   0        
HT40  LGI  1          MCS5   133      89    45.6       0.0       0.0       0     0 0             0   0        
HT40  LGI  1          MCS6   134      79    48.0       0.0       0.0       0     0 0             0   0        
HT40  LGI  1          MCS7   135      71    50.2       0.0       0.0       0     0 0             0   0        
HT40  SGI  1       S  MCS0   192     640    12.0       0.0       0.0       0     0 0             0   0        
HT40  SGI  1          MCS1   193     320    21.0       0.0       0.0       0     0 0             0   0        
HT40  SGI  1          MCS2   194     214    27.9       0.0       0.0       0     0 0             0   0        
HT40  SGI  1          MCS3   195     160    33.5       0.0       0.0       0     0 0             0   0        
HT40  SGI  1          MCS4   196     107    41.8       0.0       0.0       0     0 0             0   0        
HT40  SGI  1          MCS5   197      80    47.8       0.0       0.0       0     0 0             0   0        
HT40  SGI  1          MCS6   198      71    50.1       0.0       0.0       0     0 0             0   0        
HT40  SGI  1          MCS7   199      64    52.2       0.0       0.0       0     0 0             0   0        

Total packet count::    ideal 4      lookaround 1
Average # of aggregated frames per A-MPDU: 1.0

It looks like the rate control algorithm is not getting any information. (Also, why are no CCK rates listed? With mt7601u there are CCK rates too.)

What to do?