Re: [PATCH 0/1] wifi: rtw89: usb: Support switching to USB 3 mode

[Bitterblue Smith <rtl8821cerfe2@gmail.com>]

On 08/05/2026 08:44, Lucid Duck wrote:
> From: Devin Wittmayer <lucid_duck@justthetip.ca>
> 
> This patch adds USB 2 to USB 3 mode switching for the AX-generation
> chips in the rtw89 USB driver (8852AU, 8852BU, 8852CU and helper
> variants). Without it, those adapters enumerate at USB 2.0
> high-speed on first plug and stay there, capping real-world
> throughput around 260 Mbps TCP regardless of radio capability.
> 
> It is Bitterblue Smith's morrownr/rtw89 commit cd287ccf544b
> (2025-07-16) rebased onto wireless-next without code changes:
> author's Signed-off-by preserved, my Signed-off-by added as
> relayer, Tested-by per chip based on the matrix below.
> 
> The bug
> =======
> 
> These chips present as USB 2 devices on first plug. The driver is
> expected to send a switch-mode register write to make them disappear
> and re-enumerate as USB 3 SuperSpeed. Mainline rtw89 does not issue
> these commands anywhere. Every user with one of these adapters on
> a mainline-derived distribution sits at the USB 2.0 ceiling for
> the life of the plug, regardless of negotiated radio rate.
> 
> The fix
> =======
> 
> The patch covers AX-generation chips (8852AU, 8852BU, 8852CU and
> helper variants) via R_AX_PAD_CTRL2. It also adds the
> switch_usb_mode module parameter (default on) for users who
> experience 2.4 GHz interference under USB 3.
> 
> Mainline precedent
> ==================
> 
> The same mechanism is in mainline rtw88 across three commits
> between July 2024 and April 2025, all authored by Bitterblue Smith:
> 
>   commit 315c23a64e99 ("wifi: rtw88: usb: Support USB 3 with RTL8822CU/RTL8822BU")
>   commit 82a35723a67c ("wifi: rtw88: usb: Support USB 3 with RTL8812AU")
>   commit bf1103654df9 ("wifi: rtw88: usb: Enable switching the RTL8814AU to USB 3")
> 
> Reviewer of record: Ping-Ke Shih, current rtw89 maintainer.
> 
> Test results
> ============
> 
> 60 plug-cycles + 30+ gated throughput cells captured 2026-04-11
> to 2026-05-07. Both x86_64 (Tiger Lake xHCI) and aarch64
> (Broadcom RP1 xHCI) reproductions confirm the bug and the fix.
> 
>   Hosts:    Framework 13 (x86_64, Fedora 43 / 6.19.13, Tiger Lake xHCI)
>             NucBox K8 Plus (x86_64, Arch Linux / 6.17.9, AMD F19h USB)
>             Raspberry Pi 5 (aarch64, Pi OS / 6.12.47, BCM2712 + RP1)
>             Banana Pi BPi-R4 Pro (aarch64, OpenWrt / 6.6.93, MT7988A;
>                                   also used as a controlled lab AP)
>   Adapters: D-Link DWA-X1850 A1 / B1 (RTL8852AU)
>             BrosTrend AX1L compact / AX4L high-gain (RTL8852BU)
>             BrosTrend AX8L AXE5400 / EDUP AXE5400 (RTL8852CU)
>   APs:      consumer multi-band router (WPA3-SAE / WPA2-PSK)
>             BPi-R4 Pro single-band lab AP (WPA3-SAE)
>   Server:   Linux iperf3 host on 2.5 GbE wired Ethernet
> 
> Full per-cell evidence (raw iperf3 stdout, dmesg captures, sysfs
> snapshots, iw link snapshots, byte-counter deltas, per-host detail)
> at https://github.com/Lucid-Duck/rtw89-usb3-gap.
> 
> Plug-cycle. N=10 cycles per (chip, host) cell. Pass = post-plug
> /sys/bus/usb/devices/<id>/speed reads 5000 (USB 3 SuperSpeed),
> zero WARN/BUG/Oops in cycle-bracketed dmesg, non-empty association
> BSSID after settle.
> 
>   Adapter (chip)               FW13 6.19      K8 Plus 6.17
>   ---------------------------  -------------  --------------
>   DWA-X1850 A1 (RTL8852AU)     10/10 PASS     10/10 PASS
>   BrosTrend AX1L (RTL8852BU)   10/10 PASS     10/10 PASS
> 
>   FW13:    Fedora 43, 6.19.13, wireless-next + this patch
>   K8 Plus: Arch Linux, 6.17.9-arch1-1, morrownr/rtw89 (upstream
>            fork; identical AX-gen behavior to this patch)
> 
> Throughput. TCP iperf3, N=10 30-second iterations per sub-cell,
> four sub-cells per cell (P=8 and P=1, each direction), to a Linux
> 2.5 GbE host. Per-cell /32 host route forces traffic onto the WiFi
> adapter; per-iteration byte-counter cross-check on every cited cell
> shows wireless tx/rx delta at 103-108% of iperf3 reported bytes
> (excess is normal TCP/IP framing), so wired-NIC bleed is ruled out.
> Linux tuning applied (rmem 32 MB, RPS=ff on the WiFi RX queue).
> 
> FW13 stock (in-kernel rtw89, USB 2 stuck) vs patched (USB 3
> SuperSpeed), same adapter / AP / kernel / capture script, P=8 mean
> Mbps, AP is the consumer multi-band router:
> 
>   Adapter (chip)              Band, width      UL stock  UL patched  DL stock  DL patched
>   --------------------------  ---------------  --------  ----------  --------  ----------
>   EDUP AXE5400 (RTL8852CU)    6 GHz, 160 MHz       269        1364       327         579
>   AX8L AXE5400 (RTL8852CU)    6 GHz, 160 MHz       269        1440       324         510
>   AX4L AX1800 (RTL8852BU)     5 GHz,  80 MHz       208         597       293         695
>   AX1L AX1800 (RTL8852BU)     5 GHz,  80 MHz       235         608       273         843
>   DWA-X1850 A1 (RTL8852AU)    5 GHz,  80 MHz       254         748       264         707
>   DWA-X1850 B1 (RTL8852AU)    5 GHz,  80 MHz       248         706       265         679
> 
> USB enumeration verified at SuperSpeed (5000 Mbps) on every
> patched cell, both pre and post.
> 
> K8 Plus second-rig spot check, kernel 6.17.9-arch1-1, consumer
> multi-band router, single-link 5 GHz 80 MHz, TCP P=1, N=10:
> 
>   DWA-X1850 A1 (RTL8852AU)    788 UL / 693 DL Mbps (sigma 16 / 54)
> 
> For comparison, every stock cell above caps at 208-327 Mbps, the
> USB 2.0 ceiling.
> 
> Future work: BE-generation (RTL8922AU) USB switch-mode
> ======================================================
> 
> The same mechanism applies to BE-generation chips (RTL8922AU) via
> R_BE_PAD_CTRL2.
> The implementation is in morrownr/rtw89 commit c8a8ac49996b
> ("wifi: rtw89: usb: USB 3 switching for RTL8922AU", 2025-08-07)
> by Bitterblue Smith, but that commit has no Signed-off-by; the
> public two-week notice in
> https://github.com/morrownr/rtw89/issues/82 (2026-04-21,
> deadline 2026-05-05) did not produce one. checkpatch --strict
> rejects third-party submission on the missing trailer.
> 

This is what's stopping you? Haha.

> I tested c8a8ac49996b on a BrosTrend BE6500 (RTL8922AU): plug-
> cycle 10/10 PASS on both FW13 and K8 Plus; consumer-router MLO
> 3-link 1430 UL / 995 DL Mbps P=8; BPi-R4 Pro single-link 5 GHz
> 160 MHz EHT 1335 UL / 1058 DL Mbps P=8; switch_usb_mode=N forces
> USB 2 at 255 UL / 311 DL Mbps. Detail in the rtw89-usb3-gap repo
> above.
> 
> Adding the BE-gen switch-mode to mainline today cannot yet help
> RTL8922AU users on its own, because mainline rtw89 has no
> in-kernel rtw89_8922au USB driver: RTL8922AU adapters do not
> attach to mainline at all. Switch-mode becomes load-bearing for
> BE-gen the moment the rtw89_8922au USB driver lands upstream;
> until then it would sit as dormant code. The path upstream for
> the switch-mode itself is either Bitterblue's Signed-off-by on
> c8a8ac49996b, or a Realtek developer carrying it as part of the
> broader 8922au USB enablement.
> 
> (The AX-gen gap that this patch fixes does affect every mainline
> user with an RTL8852AU/BU/CU adapter today. BE-gen is a separate,
> strictly forward-looking concern.)
> 
> Submission notes
> ================
> 
> Applies cleanly on wireless-next HEAD 7baf5857e15d.
> checkpatch.pl --strict: zero errors, zero warnings, zero checks.
> 

Realtek wifi patches should be based on rtw-next (or rtw if it's an
urgent bug fix):

https://github.com/pkshih/rtw/

The subject should include the tree: "[PATCH rtw-next 0/1]"

> Bitterblue Smith (1):
>   wifi: rtw89: usb: Support switching to USB 3 mode
> 
>  drivers/net/wireless/realtek/rtw89/reg.h |  4 +++
>  drivers/net/wireless/realtek/rtw89/usb.c | 41 ++++++++++++++++++++++++
>  2 files changed, 45 insertions(+)
> 
> --
> 2.53.0
>