[PATCH] wifi: mt76: mt7915: fix GENMASK for chain 3 RSSI in mt7915_mac_sta_poll()

[PATCH] wifi: mt76: mt7915: fix GENMASK for chain 3 RSSI in mt7915_mac_sta_poll()

[Ankit Dange]

The RCPI values of response frames are stored as four consecutive
bytes in WTBL DW30. The bitmask for extracting chain 3 RCPI uses
GENMASK(31, 14) which is an 18-bit field overlapping with chains 1
and 2. Fix it to GENMASK(31, 24) to correctly extract the 8-bit
RCPI value for chain 3.

On devices with fewer than 4 antenna chains this bug is masked
because mt76_rx_signal() skips chains not present in antenna_mask.
On 4x4 configurations the corrupted chain 3 value feeds into the
combined ACK signal strength calculation.

Tested on Yuncore AX820 (MT7915, 2x2) by reading raw DW30 register
values and comparing FIELD_GET results for both masks. With
GENMASK(31, 14), chain 3 produces garbage values (e.g., -112 dBm
from a register value of 0xFFFF4248 where the correct result is
+17, indicating an unused chain). No regression on 2x2 operation.

Fixes: 94b335fa88e1 ("wifi: mt76: mt7915: add ack signal support")
Signed-off-by: Ankit Dange <ankitdange37@gmail.com>
---
 mt7915/mac.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mt7915/mac.c b/mt7915/mac.c
index b581d8f9..3d7d71ac 100644
--- a/mt7915/mac.c
+++ b/mt7915/mac.c
@@ -221,7 +221,7 @@ static void mt7915_mac_sta_poll(struct mt7915_dev *dev)
 		rssi[0] = to_rssi(GENMASK(7, 0), val);
 		rssi[1] = to_rssi(GENMASK(15, 8), val);
 		rssi[2] = to_rssi(GENMASK(23, 16), val);
-		rssi[3] = to_rssi(GENMASK(31, 14), val);
+		rssi[3] = to_rssi(GENMASK(31, 24), val);
 
 		msta->ack_signal =
 			mt76_rx_signal(msta->vif->phy->mt76->antenna_mask, rssi);
-- 
2.43.0