Re: rtw88: RTL8812BU TX FIFO corruption (?) in USB 3 mode

[Bitterblue Smith <rtl8821cerfe2@gmail.com>]

On 26/03/2025 03:44, Ping-Ke Shih wrote:
> Bitterblue Smith <rtl8821cerfe2@gmail.com> wrote:
>> Hi,
>>
>> I ran into a problem with the RTL8812BU. If I load it a bit in USB 3
>> mode, like with "iperf3 -c 192.168.0.1 -R -t 60" the connection often
>> stops working. It may take a few tries. It still receives beacons but
>> the AP can't be pinged anymore.
>>
>> Looking at the registers with
>> "watch cat /sys/kernel/debug/ieee80211/phy*/rtw88/mac_2", I noticed
>> the high half of register 0x240 was steadily increasing.
>>
>> Register 0x240 is called REG_FIFOPAGE_INFO_5. The driver writes the
>> number of pages allocated to the public queue into the low half.
>> The high half indicates the number of pages currently available.
>> The number of available pages was steadily increasing, beyond the
>> total number of pages:
>>
>> 00000240  072b070b    0003fa00    0003fe00    0003fa60
>> 00000240  0737070b    0003fa00    0003fe00    0003fa60
>> 00000240  073b070b    0003fa00    0003fe00    0003fa60
>> 00000240  0741070b    0003fa00    0003fe00    0003fa60
>> 00000240  0741070b    0003fa00    0003fe00    0003fa60
>> 00000240  074f070b    0003fa00    0003fe00    0003fa60
>> 00000240  075d070b    0003fa00    0003fe00    0003fa60
>>
>> Normal values when the device is functional (and idle):
>>
>> 00000240  070b070b    0003fa00    0003fe00    0003fa60
>>
>> When register 0x240 has strange values, register 0x210
>> (REG_TXDMA_STATUS) has the value 5. Normally register 0x210 is 0.
>>
>> All this only happens in USB 3 mode. Everything is fine in USB 2 mode.
> 
> I checked with internal USB team. The USB 3 mode can only work on 5GHz,
> because electrical interference between USB 3 clock and WiFi 2.4 GHz
> band. Could you check if it works on 5GHz?
> 

Thank you for taking this to them.

It doesn't work on 5 GHz. I was already using my 5 GHz network on
channel 100.

>>
>> I tried to disable USB RX and TX aggregation, SUPPORTS_AMSDU_IN_AMPDU,
>> and TX_AMSDU. None of that helped.
>>
>> This problem happens also with this driver:
>> https://github.com/morrownr/88x2bu-20210702
>> and with v5.13.1.1-1-g6f2541ef2.20240507_COEX20220812-18317b7b.
> 
> By default, it only supports USB 2 mode. Have you changed the driver?
> 

I did not change the driver. I set the module parameter
rtw_switch_usb_mode to 1. It makes the driver switch to USB 3 mode.

I forgot to say that I also tested Windows 10 with the driver from
TP-Link (I think). I tried alternating upload tests and download
tests over and over, I left iperf3 running for many minutes. It was
very difficult to make it fail. I think only one time iperf3
reported 0 speed for a few seconds but it recovered by itself.
I don't know how to examine the hardware registers (0x210, 0x240)
in Windows, so I can't say for sure that the problem doesn't happen
there. But it looks much better than in Linux. It was definitely
in USB 3 mode, the speeds were 500-600 Mbps.

>> I see
>> the same strange values in register 0x240 in
>> /proc/net/rtl88x2bu/wlp3s0f3u4/mac_reg_dump.
>>
>> My test device is TP-Link Archer T3U Plus, with USB ID 2357:0138.
>> My system is Lenovo Ideapad 3 15ADA6 with AMD Athlon Gold 3150U CPU.
>>
>> Can this be fixed somehow? I saw the other drivers have some code in
>> rtw_sreset.c to power off and on the device when register 0x210 is
>> non-zero, but that seems suboptimal.