[PATCH v3 0/1] wifi: mt76: mt7921: fix txpower reporting from rate power configuration

[Lucid Duck]

Sean, Felix,

Here's v3 of the txpower fix, reworked based on both of your feedback.

Felix pointed out in v1 review that the fix should determine the maximum
rate power from the loop in mt76_connac_mcu_rate_txpower_band(). Sean
confirmed this direction in v2 review and clarified that the value should
come from the same computation that configures the firmware's per-rate
power tables, not from bss_conf.txpower.

v3 does exactly that. The loop already computes the right value via
mt76_get_rate_power_limits() but discards the return. This patch
captures it and stores it to phy->txpower_cur for the current channel,
matching how mt7915 handles this in mt7915_mcu_set_txpower_sku().
Nick independently confirmed v2 produced correct values on his
MT7921AU -- v3 preserves those results while addressing the
source-of-truth concern.

Two additional issues came up during implementation:

- mt7921's chanctx callbacks don't update phy->chandef (the common
  mt76_add_chanctx does, but mt7921 overrides it with a minimal
  version). Fixed by syncing chandef from ctx->def and re-triggering
  the rate power path in add_chanctx and change_chanctx.

- For chanctx drivers, mac80211 routes iw set txpower through
  BSS_CHANGED_TXPOWER, not IEEE80211_CONF_CHANGE_POWER, and never
  updates hw->conf.power_level. Added a BSS_CHANGED_TXPOWER handler
  to bridge this into the rate power path.

Tested on Alfa AWUS036AXML (MT7921AU), kernel 6.17.1, Canada:

  Band       Auto       User limit (15dBm)   Stock (before)
  2.4GHz     33 dBm     18 dBm               3 dBm
  5GHz       26 dBm     18 dBm               3 dBm
  6GHz       15 dBm      8 dBm (5dBm limit)  3 dBm

  Values match regulatory limits + 3 dBm 2x2 path delta.

Test suite (973 tests, 3.5 hours):

  Regulatory accuracy:     correct on all 3 bands (2.4/5/6 GHz)

  User txpower sweep:      every 1 dBm from 1 to reg_max, all 3 bands

  Band switching:          100 cycles between 2.4 and 5 GHz, 0 failures

  Module reload:           50 rmmod/insmod/connect/verify cycles, 0 failures

  2-hour soak:             480 samples at 15s intervals, zero drift

  Band rotation soak:      30 rotations across all 3 bands over 1 hour,
                           240 samples, 0 failures

  Regdomain switching:     10 countries (CA/US/JP/DE/GB/AU/NZ/BR/KR/TW)
                           mid-session without reconnecting, all correct
                           (JP correctly dropped to 23 dBm on 5GHz UNII-1)

  Monitor mode:            correct on ch1/6/11 (2.4GHz) and ch36/44/149
                           (5GHz), txpower set works in monitor mode

  Edge cases:              min power (1dBm), over-max clamping, rapid
                           power changes (10 in 10s), all correct

  Firmware cross-check:    debugfs txpower_sku confirms per-rate tables
                           match regulatory limits on all bands

Lucid Duck (1):
  wifi: mt76: mt7921: fix txpower reporting from rate power
    configuration

 .../wireless/mediatek/mt76/mt76_connac_mcu.c  | 12 +++++++---
 .../net/wireless/mediatek/mt76/mt7921/main.c  | 22 ++++++++++++++++++-
 2 files changed, 30 insertions(+), 4 deletions(-)

--
2.51.0