Re: [PATCH v3] wifi: rtw89: phy: increase RF calibration timeouts for USB transport

[Ping-Ke Shih]

Louis Kotze <loukot@xxxxxxxxx> wrote:

> USB transport adds significant latency to H2C/C2H round-trips used
> by RF calibration. The existing timeout values were designed for PCIe
> and are too tight for USB, causing "failed to wait RF DACK",
> "failed to wait RF TSSI" and similar errors on USB adapters.
> 
> Apply a 4x timeout multiplier when the device uses USB transport.
> The multiplier is applied in rtw89_phy_rfk_report_wait() so all
> calibrations benefit without changing any call sites or PCIe
> timeout values.
> 
> The 4x multiplier was chosen based on measured data from two
> independent testers (RTL8922AU, 6GHz MLO and 2.4/5GHz):
> 
>   Calibration   PCIe timeout   Max measured (USB)   4x timeout
>   PRE_NTFY           5ms              1ms              20ms
>   DACK              58ms             72ms             232ms
>   RX_DCK           128ms            374ms             512ms
>   TSSI normal       20ms             24ms              80ms
>   TSSI scan          6ms             14ms              24ms
>   TXGAPK            54ms             18ms             216ms
>   IQK               84ms             53ms             336ms
>   DPK               34ms             30ms             136ms
> 
> Tested with RTL8922AU on 6GHz MLO (5GHz + 6GHz simultaneous):
> 25 connect/disconnect cycles with zero failures.
> 
> The 4x multiplier was also verified under adverse host conditions
> on 5GHz. 5 cycles per scenario, stress-ng as the load generator,
> max observed time per calibration:
> 
>   Calibration  PCIe  4x   Baseline  CPU stress  Mem stress  Combined
>   PRE_NTFY       5   20     0         0           0           1
>   DACK          58  232    71 (!)    71 (!)      71 (!)      71 (!)
>   RX_DCK       128  512    23        22          22          23
>   IQK           84  336    53        53          53          53
>   DPK           34  136    23        23          26          23
>   TSSI          20   80     6         9          14           9
>   TXGAPK        54  216    16        16          16          16
> 
> Legend: (!) = exceeds PCIe budget but within 4x budget.
> 
> Two observations from that matrix:
> 
> 1. DACK exceeds the stock PCIe budget (58ms) in baseline on 5GHz
>    on this hardware. Without the 4x multiplier, DACK fails
>    -ETIMEDOUT deterministically on every connect, no stress
>    needed. This is the condition the patch addresses.
> 
> 2. Calibration times appear dominated by USB transport round-trip
>    latency rather than host load, though hardware and external
>    component factors may also contribute. DACK stays at 71ms
>    across all four scenarios. Host-side stress has essentially
>    zero effect on observed calibration duration. Bumping the
>    multiplier above 4x would not address a failure mode that
>    this stress matrix produces.
> 
> Reported-by: Devin Wittmayer <lucid_duck@xxxxxxxxxxxxx>
> Link: https://github.com/Lucid-Duck/rtw89-usb3-gap/tree/main/evidence/crash-2026-04-11
> Signed-off-by: Louis Kotze <loukot@xxxxxxxxx>
> Tested-by: Devin Wittmayer <lucid_duck@xxxxxxxxxxxxx> # RTL8922AU (BrosTrend BE6500)
> Tested-by: Devin Wittmayer <lucid_duck@xxxxxxxxxxxxx> # RTL8852AU (D-Link DWA-X1850 A1)
> Tested-by: Devin Wittmayer <lucid_duck@xxxxxxxxxxxxx> # RTL8852AU (D-Link DWA-X1850 B1)
> Tested-by: Devin Wittmayer <lucid_duck@xxxxxxxxxxxxx> # RTL8852BU (BrosTrend AX4L)
> Tested-by: Devin Wittmayer <lucid_duck@xxxxxxxxxxxxx> # RTL8852CU (EDUP AX5400)
> Acked-by: Ping-Ke Shih <pkshih@xxxxxxxxxxx>

1 patch(es) applied to rtw-next branch of rtw.git, thanks.

5055188134c3 wifi: rtw89: phy: increase RF calibration timeouts for USB transport

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