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Linville" , linux-wireless@vger.kernel.org (open list:B43 WIRELESS DRIVER), b43-dev@lists.infradead.org (open list:B43 WIRELESS DRIVER) Subject: [PATCH wireless] wifi: b43: back off the N-PHY TX power per rate Date: Thu, 15 Oct 2026 10:59:28 -0700 Message-ID: <20261015175928.3558057-1-rosenp@gmail.com> X-Mailer: git-send-email 2.56.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On N-PHY rev 3+ the hardware TX power control aims at the highest per-rate target, and an adjusted power table backs each rate group off from it. b43 fills that table from nphy->tx_power_offset[], but never sets the offsets, so they stay zero and every rate is sent at the power allowed for CCK. The SPROM power offsets exist to avoid this: on boards with external PAs, OFDM and MCS rates have to be sent a few dB lower than CCK to keep the PA linear. Sent at full power, 16-QAM and 64-QAM frames are too distorted to decode. On an ASUS RT-N16 (BCM4718, N-PHY rev 5, radio 2056, ofdm2gpo 0x66666666) the router could only send at 6-18 Mbit/s and MCS 0-2, even at -50 dBm, and 24 Mbit/s and up or MCS 3 and up delivered nothing. Set the offsets from the per-rate targets b43 already computes from the SPROM, as brcmsmac does, before the table is built. With this, the RT-N16 sends at 54 Mbit/s, and at MCS 7 with HT enabled, and TCP from the router to a client goes from 9 to 17-18 Mbit/s. Fixes: 8615eb2870f1 ("b43: N-PHY: support setting custom TX power") Assisted-by: LLM Signed-off-by: Rosen Penev --- drivers/net/wireless/broadcom/b43/phy_n.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c index 22359bd9db47..c9b2b7496983 100644 --- a/drivers/net/wireless/broadcom/b43/phy_n.c +++ b/drivers/net/wireless/broadcom/b43/phy_n.c @@ -5834,6 +5834,7 @@ static enum b43_txpwr_result b43_nphy_op_recalc_txpower(struct b43_wldev *dev, struct ieee80211_channel *channel = dev->wl->hw->conf.chandef.chan; struct b43_ppr *ppr = &nphy->tx_pwr_max_ppr; u8 max; /* qdBm */ + int i; if (nphy->tx_pwr_last_recalc_freq == channel->center_freq && nphy->tx_pwr_last_recalc_limit == phy->desired_txpower) @@ -5868,6 +5869,16 @@ static enum b43_txpwr_result b43_nphy_op_recalc_txpower(struct b43_wldev *dev, /* Make sure we didn't go too low */ b43_ppr_apply_min(dev, ppr, INT_TO_Q52(8)); + /* + * The hardware power control aims at the highest per-rate target. + * The adjusted power table backs other rates off from it, so that + * e.g. 64-QAM isn't sent at the power allowed for CCK. + */ + max = b43_ppr_get_max(dev, ppr); + memset(nphy->tx_power_offset, 0, sizeof(nphy->tx_power_offset)); + for (i = 0; i < B43_PPR_RATES_NUM; i++) + nphy->tx_power_offset[i] = max - ppr->__all_rates[i]; + /* Apply */ b43_mac_suspend(dev); b43_nphy_tx_power_ctl_setup(dev); -- 2.56.0