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

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

[Louis Kotze]

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@justthetip.ca>
Link: https://github.com/Lucid-Duck/rtw89-usb3-gap/tree/main/evidence/crash-2026-04-11
Signed-off-by: Louis Kotze <loukot@gmail.com>
Tested-by: Devin Wittmayer <lucid_duck@justthetip.ca> # RTL8922AU (BrosTrend BE6500)
Tested-by: Devin Wittmayer <lucid_duck@justthetip.ca> # RTL8852AU (D-Link DWA-X1850 A1)
Tested-by: Devin Wittmayer <lucid_duck@justthetip.ca> # RTL8852AU (D-Link DWA-X1850 B1)
Tested-by: Devin Wittmayer <lucid_duck@justthetip.ca> # RTL8852BU (BrosTrend AX4L)
Tested-by: Devin Wittmayer <lucid_duck@justthetip.ca> # RTL8852CU (EDUP AX5400)
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
---
Changes since v2:
  - Reword commit message per Ping-Ke review: remove v1 reference
    from permanent changelog, use "condition" instead of "bug",
    acknowledge hardware factors in calibration timing rather than
    asserting I/O bound.
  - Add Tested-by tags from Devin Wittmayer across 4 chipsets
    (RTL8922AU, RTL8852AU, RTL8852BU, RTL8852CU) on Framework 13 +
    Fedora 43 (6.19.11) and Raspberry Pi 5 + Pi OS (6.12.47).
  - Add Reported-by for independent confirmation including xHCI hard
    lockup evidence (CPU5 deadlock in usb_unanchor_urb after DACK
    timeout triggered driver recovery).

v2: https://lore.kernel.org/linux-wireless/20260415111339.453602-1-loukot@gmail.com/
v1: https://lore.kernel.org/linux-wireless/20260410080017.82946-1-loukot@gmail.com/

 drivers/net/wireless/realtek/rtw89/phy.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/wireless/realtek/rtw89/phy.c b/drivers/net/wireless/realtek/rtw89/phy.c
index e70d0e283..1f249c297 100644
--- a/drivers/net/wireless/realtek/rtw89/phy.c
+++ b/drivers/net/wireless/realtek/rtw89/phy.c
@@ -3956,6 +3956,14 @@ int rtw89_phy_rfk_report_wait(struct rtw89_dev *rtwdev, const char *rfk_name,
 	struct rtw89_rfk_wait_info *wait = &rtwdev->rfk_wait;
 	unsigned long time_left;
 
+	/*
+	 * USB transport adds latency to H2C/C2H round-trips, so RF
+	 * calibrations take longer than on PCIe. Apply a 4x multiplier
+	 * to avoid spurious timeouts.
+	 */
+	if (rtwdev->hci.type == RTW89_HCI_TYPE_USB)
+		ms *= 4;
+
 	/* Since we can't receive C2H event during SER, use a fixed delay. */
 	if (test_bit(RTW89_FLAG_SER_HANDLING, rtwdev->flags)) {
 		fsleep(1000 * ms / 2);

base-commit: 1e33ef7657531b2361d53cca25f375b5626e76a9
-- 
2.53.0