[PATCH] wifi: mt76: mt7925: Fix EHT Beamformee SS subfields to meet 802.11be minimum

[JB Tsai]

From: "shengwei.lu" <shengwei.lu at mediatek.com>

Per IEEE 802.11be, the Beamformee SS <= 80/160/320 MHz 3-bit subfields
in the EHT PHY Capabilities are encoded as (Nss - 1) and are required
to be >= 3 (i.e. at least 4 SS receive capability) whenever SU
Beamformee is advertised.

MT7925 is a 2x2 STA (sts = 2), so directly filling (sts - 1) = 1
violates the spec minimum. Clamp the encoded value to 3 when sts <= 3,
otherwise use (sts - 1). This is applied consistently to the
BEAMFORMEE_SS <= 80 MHz (split across phy_cap_info[0]/[1]), <= 160 MHz
and <= 320 MHz (6 GHz only) subfields.

Fixes: c948b5da6bbe ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips")
Signed-off-by: shengwei.lu <shengwei.lu at mediatek.com>
---
 drivers/net/wireless/mediatek/mt76/mt7925/main.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/main.c b/drivers/net/wireless/mediatek/mt76/mt7925/main.c
index ddb637d6a3c3..dbe67ce2e4a2 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/main.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/main.c
@@ -188,19 +188,21 @@ mt7925_init_eht_caps(struct mt792x_phy *phy, enum nl80211_band band,
 		eht_cap_elem->phy_cap_info[0] |=
 			IEEE80211_EHT_PHY_CAP0_320MHZ_IN_6GHZ;
 
+	val = (sts > 3) ? sts - 1 : 3;
+
 	eht_cap_elem->phy_cap_info[0] |=
-		u8_encode_bits(u8_get_bits(sts - 1, BIT(0)),
+		u8_encode_bits(u8_get_bits(val, BIT(0)),
 			       IEEE80211_EHT_PHY_CAP0_BEAMFORMEE_SS_80MHZ_MASK);
 
 	eht_cap_elem->phy_cap_info[1] =
-		u8_encode_bits(u8_get_bits(sts - 1, GENMASK(2, 1)),
+		u8_encode_bits(u8_get_bits(val, GENMASK(2, 1)),
 			       IEEE80211_EHT_PHY_CAP1_BEAMFORMEE_SS_80MHZ_MASK) |
-		u8_encode_bits(sts - 1,
+		u8_encode_bits(val,
 			       IEEE80211_EHT_PHY_CAP1_BEAMFORMEE_SS_160MHZ_MASK);
 
 	if (band == NL80211_BAND_6GHZ && is_320mhz_supported(&phy->dev->mt76))
 		eht_cap_elem->phy_cap_info[1] |=
-			u8_encode_bits(sts - 1,
+			u8_encode_bits(val,
 				       IEEE80211_EHT_PHY_CAP1_BEAMFORMEE_SS_320MHZ_MASK);
 
 	eht_cap_elem->phy_cap_info[2] =
-- 
2.45.2