[PATCH] staging: rtl8723bs: fix inverted HT40 secondary channel offset

[teirua <qndkdrnl@gmail.com>]

From: MinJea Kim <qndkdrnl@gmail.com>

rtw_get_chan_type() maps the driver's channel offset to nl80211 channel
types the wrong way around.

In this driver HAL_PRIME_CHNL_OFFSET_LOWER means the primary channel is
the lower 20 MHz half of the 40 MHz pair, i.e. the secondary channel is
above the primary one: rtw_get_center_ch() computes the center channel
as "channel + 2" for OFFSET_LOWER, and bwmode_update_check() sets
OFFSET_LOWER when the AP's HT operation IE announces SCA (secondary
channel above). In nl80211 terms that is NL80211_CHAN_HT40PLUS, not
HT40MINUS.

Because of the inversion, cfg80211_rtw_get_channel() reports an HT40+
association as HT40-. For an HT40+ AP on a low channel (e.g. channel 3)
the resulting chandef spans below the 2.4 GHz band edge and is invalid,
so the regulatory core tears the connection down 60 seconds
(REG_ENFORCE_GRACE_MS) after the AP's country IE triggers a regdomain
change: reg_check_chans_work() considers the reported chandef unusable
and calls cfg80211_leave(). The supplicant then reconnects, the country
IE changes the regdomain again, and the cycle repeats, causing a
disconnect/reconnect loop every ~65 seconds for as long as the link is
up.

Observed on a TECLAST X80 Power tablet (RTL8723BS) associated to an
HT40+ AP on channel 3 with a KR country IE; a kprobe trace showed
cfg80211_disconnect() being invoked from reg_check_chans_work(). With
the mapping fixed, "iw dev wlan0 info" reports the correct
"width: 40 MHz, center1: 2432 MHz" and the periodic disconnects stop.

Fixes: 5402cc178c5d ("staging: rtl8723bs: add get_channel cfg80211 implementation")
Cc: stable@vger.kernel.org
Assisted-by: Claude-Code:claude-fable-5 bpftrace
Signed-off-by: MinJea Kim <qndkdrnl@gmail.com>
---
 drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c b/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c
index 1484336..e472687 100644
--- a/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c
+++ b/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c
@@ -1949,7 +1949,12 @@ static u8 rtw_get_chan_type(struct adapter *adapter)
 		else
 			return NL80211_CHAN_NO_HT;
 	case CHANNEL_WIDTH_40:
-		if (mlme_ext->cur_ch_offset == HAL_PRIME_CHNL_OFFSET_UPPER)
+		/*
+		 * HAL_PRIME_CHNL_OFFSET_LOWER means the primary channel is
+		 * the lower 20 MHz half, i.e. the secondary channel sits
+		 * above it (SCA), which is NL80211_CHAN_HT40PLUS.
+		 */
+		if (mlme_ext->cur_ch_offset == HAL_PRIME_CHNL_OFFSET_LOWER)
 			return NL80211_CHAN_HT40PLUS;
 		else
 			return NL80211_CHAN_HT40MINUS;
-- 
2.43.0