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

Louis Kotze
2026-04-15T11:13:54Z

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, 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.

2. Calibration times are I/O bound (USB H2C/C2H round-trip
latency), 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>
---
Changes since v1:
- Fix comment style per Ping-Ke Shih review (first line '/*' on its
own line, kernel-standard format).
- Add stress-test verification table to the commit message. The 4x
multiplier was re-measured on 5GHz under CPU stress, memory stress,
and combined stress using stress-ng. DACK max is 71ms in all four
scenarios, confirming calibration times are I/O bound (USB H2C/C2H
round-trip) and not affected by host-side load.
- Drop v1 patch 2/2 ("make RF calibration timeouts non-fatal on USB").
As Ping-Ke noted, the return code from rtw89_phy_rfk_*_and_wait() is
discarded by all 8922a callers, making the non-fatal change a no-op
for 8922a. Worse, the one 8922d caller that does check the return
(rtw8922d_rfk_tssi) uses it to fall back to non-TSSI mode on
calibration failure — patch 2/2 would have silently broken that
fallback. With patch 1/2's multiplier alone, 25 connect/disconnect
cycles complete with zero failures, and the new stress matrix above
confirms the margin.

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);
--
2.53.0