[PATCH wireless] wifi: mt76: mt7925: don't put the band auto marker in TGID

[Devin Wittmayer]

band_idx starts out as 0xff, which tells the firmware to pick the band on
its own. A remain-on-channel grant normally writes a real index over it
before anything else looks. Two cases never see that: an MLD station
throws the grant away, and an AP has no association to trigger one.

The TX descriptor reads the same field into a two-bit slot, so the marker
comes out as 3. Every data frame from those two goes out tagged band 3.
Beacons are fine, they reach the firmware separately and never build a
descriptor.

Same numbers on an MT7925 and on a Netgear A9000:

                        stock         patched
  station, one link     0x00000001    0x00000001
  station, two links    0x00003001    0x00000001
  AP                    0x00003013    0x00000013
  real band index, STA  0x00001001    0x00001001
  real band index, AP   0x00001013    0x00001013

Only the marker cases move.

Fixes: 0cb349d742d1 ("wifi: mt76: mt7925: update mt7925_mac_link_bss_add for MLO")
Signed-off-by: Devin Wittmayer <lucid_duck at justthetip.ca>
---
 drivers/net/wireless/mediatek/mt76/mt7925/mac.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/mac.c b/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
index 101f571b0..3b82c9de2 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
@@ -798,7 +798,8 @@ mt7925_mac_write_txwi(struct mt76_dev *dev, __le32 *txwi,
 	val = FIELD_PREP(MT_TXD1_WLAN_IDX, wcid->idx) |
 	      FIELD_PREP(MT_TXD1_OWN_MAC, omac_idx);
 
-	if (band_idx)
+	/* 0xff means BAND_AUTO to the firmware, and TGID cannot encode it */
+	if (band_idx && band_idx != 0xff)
 		val |= FIELD_PREP(MT_TXD1_TGID, band_idx);
 
 	txwi[1] = cpu_to_le32(val);