mt76: dma: add skb check for dummy pointer

Introduce skb check for dummy address in mt76_dma_tx_cleanup_idx.
This is a preliminary patch to add support for new chipsets (e.g. 7615)
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/dma.c

@@ -18,8 +18,6 @@
 #include "mt76.h"
 #include "dma.h"
 
-#define DMA_DUMMY_TXWI	((void *) ~0)
-
 static int
 mt76_dma_alloc_queue(struct mt76_dev *dev, struct mt76_queue *q,
 		     int idx, int n_desc, int bufsize,
@@ -67,7 +65,7 @@ mt76_dma_add_buf(struct mt76_dev *dev, struct mt76_queue *q,
 	int i, idx = -1;
 
 	if (txwi)
-		q->entry[q->head].txwi = DMA_DUMMY_TXWI;
+		q->entry[q->head].txwi = DMA_DUMMY_DATA;
 
 	for (i = 0; i < nbufs; i += 2, buf += 2) {
 		u32 buf0 = buf[0].addr, buf1 = 0;
@@ -126,9 +124,12 @@ mt76_dma_tx_cleanup_idx(struct mt76_dev *dev, struct mt76_queue *q, int idx,
 				 DMA_TO_DEVICE);
 	}
 
-	if (e->txwi == DMA_DUMMY_TXWI)
+	if (e->txwi == DMA_DUMMY_DATA)
 		e->txwi = NULL;
 
+	if (e->skb == DMA_DUMMY_DATA)
+		e->skb = NULL;
+
 	*prev_e = *e;
 	memset(e, 0, sizeof(*e));
 }

drivers/net/wireless/mediatek/mt76/dma.h

@@ -16,6 +16,8 @@
 #ifndef __MT76_DMA_H
 #define __MT76_DMA_H
 
+#define DMA_DUMMY_DATA			((void *)~0)
+
 #define MT_RING_SIZE			0x10
 
 #define MT_DMA_CTL_SD_LEN1		GENMASK(13, 0)