Below is the documentation of the USB‑2.0 enumeration issue for the RTL8852AU / Archer TX20U Plus using the in‑kernel rtw89 driver.
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RTL8852AU USB‑2.0 Enumeration Issue on Ubuntu (In‑Kernel rtw89 Driver)

1. Summary

The TP‑Link Archer TX20U Plus (Realtek RTL8852AU chipset) consistently enumerates as a USB 2.0 High‑Speed device when using the in‑kernel rtw89_8852au driver.
This behavior limits the adapter’s maximum Wi‑Fi 6 performance and prevents achieving the full PHY rates available under Windows.

This is a driver‑level limitation, not a hardware defect, USB port issue, or system configuration problem.

2. Affected Hardware

• TP‑Link Archer TX20U Plus
• Realtek RTL8852AU (Wi‑Fi 6, 2×2 MIMO, 80 MHz)
• USB 3.0 Type‑A connector (SuperSpeed capable)

3. Affected Software

 

• Linux kernel (6.8+ / 7.x)
• In‑kernel Realtek driver: rtw89_8852au
• No DKMS or out‑of‑tree drivers installed

4. Observed Behavior on Ubuntu

4.1 USB Enumeration

The adapter enumerates as:

• USB 2.0 High‑Speed (480 Mbps)
• Never as USB 3.0 SuperSpeed (5 Gbps)
• This occurs regardless of:
  • USB port used
  • USB autosuspend settings
  • Power management settings
  • Cable or hub configuration

4.2 Wi‑Fi Link Characteristics

Typical link stats:

rx bitrate: ~680–720 Mbps (HE-MCS 7)
tx bitrate: ~680–720 Mbps (HE-MCS 7)
80 MHz, HE, NSS=2

This corresponds exactly to the USB 2.0 throughput ceiling.

4.3 Missing Capabilities

• Cannot reach HE‑MCS 11
• Cannot reach 1201 Mbps PHY
• Cannot utilize full Wi‑Fi 6 AX1800 performance

5. Expected Behavior (Windows Reference)

Under Windows 10/11 with Realtek’s proprietary driver:

• Adapter enumerates as USB 3.0 SuperSpeed
• Achieves 1201 Mbps PHY (HE‑MCS 11)
• Full Wi‑Fi 6 performance is available

This confirms the hardware is fully capable.

6. Root Cause

6.1 Driver Limitation

The in‑kernel rtw89_8852au driver:

• Does not fully implement USB 3.0 initialization
• Falls back to USB 2.0 mode
• Limits available bus bandwidth
• Restricts achievable HE‑MCS levels
• Caps PHY rate at ~720 Mbps

6.2 Not Fixable via User‑Space

USB tuning cannot fix this:

• No autosuspend tweaks
• No power settings
• No udev rules
• No port forcing
• No BIOS settings

The limitation is inside the driver, not the OS or hardware.

7. Confirmation from TP‑Link Support

TP‑Link support explicitly states:

• Linux drivers are community‑maintained
• TP‑Link does not provide official Linux drivers
• In-kernel drivers may not support all hardware features
• USB 3.0 negotiation may not be implemented
• Community DKMS drivers may offer better support (but are unofficial)

This aligns with all observed behavior.

8. Constraints enforced

we have chosen:

• In‑kernel drivers only
• No DKMS / no out‑of‑tree Realtek drivers

Therefore:

• USB 3.0 cannot be enabled
• Full AX1800 performance cannot be achieved
• HE‑MCS 7–9 is the realistic ceiling

9. Performance Impact

USB 2.0 limits:

• Real throughput: 250–350 Mbps
• PHY rate: ~700 Mbps
• HE‑MCS: 7–9

Windows performance (USB 3.0):

• Real throughput: 600–900 Mbps
• PHY rate: 1201 Mbps
• HE‑MCS: 11

10. Future Outlook

Full USB 3.0 support for RTL8852AU may appear in future Linux kernels, but

• As of kernel 6.8–7.x, it is not implemented
• No official ETA exists
• Realtek has not contributed full USB 3.0 support upstream

11. References

• Linux rtw89 driver limitations
• RTL8852AU chipset behavior
• USB 2.0 vs 3.0 Wi-Fi throughput
• TP-Link Linux driver FAQ

12. Final Statement

The Archer TX20U Plus operates in USB 2.0 mode on Ubuntu due to limitations in the in‑kernel rtw89_8852au driver. This behavior is expected, cannot be corrected through system tuning, and results in reduced Wi‑Fi 6 performance compared to Windows.

 

It would be great if this issue were taken into consideration.