RE: [PATCH v2] wifi: rtw89: phy: increase RF calibration timeouts for USB transport

[Ping-Ke Shih <pkshih@realtek.com>]

Louis Kotze <loukot@gmail.com> 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.
> 
> In response to review feedback on v1, 

Can we remove this phrase? No need to mention v1 in commit message. 

> the 4x multiplier was also
> re-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 specific bug the patch fixes.

I'm not sure this should be called "bug", as Bitterblue has not adjusted
these timeout time by earlier version. 

> 
> 2. Calibration times are I/O bound (USB H2C/C2H round-trip
>    latency), 

I'm also not sure if this is correct. The calibration time of DACK might
rely on WiFi hardware and external components, not only I/O speed. 

> not CPU or memory bound. 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.
> 
> Signed-off-by: Louis Kotze <loukot@gmail.com>

Otherwise, patch content looks good to me.

Acked-by: Ping-Ke Shih <pkshih@realtek.com>