[PATCH 2/3] wifi: mt76: mt7925: drop TXRX_NOTIFY on non-mmio buses

[Devin Wittmayer]

PKT_TYPE_TXRX_NOTIFY is an mmio-only event, but mt7925_rx_check() and
mt7925_queue_rx_skb() dispatch it to mt7925_mac_tx_free() on every bus.
mt7925_mac_tx_free() cleans the DMA tx queues with
mt76_queue_tx_cleanup(), which calls queue_ops->tx_cleanup(). Only the
mmio queue ops implement that callback; on USB it is NULL, so a
TXRX_NOTIFY there calls a NULL pointer in the RX worker:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:0x0
  Call Trace:
   mt7925_mac_tx_free+0x58/0x350 [mt7925_common]
   mt7925_rx_check+0xe2/0x130 [mt7925_common]
   mt76u_rx_worker+0x1b9/0x620 [mt76_usb]

Drop the event on non-mmio buses via mt76_is_mmio(), as in
commit 5683e1488aa9 ("wifi: mt76: connac: do not check WED status for
non-mmio devices").

Fixes: c948b5da6bbe ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Devin Wittmayer <lucid_duck@xxxxxxxxxxxxx>
---
 drivers/net/wireless/mediatek/mt76/mt7925/mac.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/mac.c b/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
index 0641a7131d7c..2f9871792ea1 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/mac.c
@@ -1203,8 +1203,9 @@ bool mt7925_rx_check(struct mt76_dev *mdev, void *data, int len)
 
 	switch (type) {
 	case PKT_TYPE_TXRX_NOTIFY:
-		/* PKT_TYPE_TXRX_NOTIFY can be received only by mmio devices */
-		mt7925_mac_tx_free(dev, data, len); /* mmio */
+		if (!mt76_is_mmio(mdev))
+			return false;
+		mt7925_mac_tx_free(dev, data, len);
 		return false;
 	case PKT_TYPE_TXS:
 		for (rxd += 4; rxd + 12 <= end; rxd += 12)
@@ -1240,7 +1241,10 @@ void mt7925_queue_rx_skb(struct mt76_dev *mdev, enum mt76_rxq_id q,
 
 	switch (type) {
 	case PKT_TYPE_TXRX_NOTIFY:
-		/* PKT_TYPE_TXRX_NOTIFY can be received only by mmio devices */
+		if (!mt76_is_mmio(mdev)) {
+			napi_consume_skb(skb, 1);
+			break;
+		}
 		mt7925_mac_tx_free(dev, skb->data, skb->len);
 		napi_consume_skb(skb, 1);
 		break;
-- 
2.54.0