mt76: fix double DMA unmap of the first buffer on 7615/7915

A small part of the first skb buffer is passed to the firmware for parsing
via DMA, while the full buffer is passed as part of the TXP.

Avoid calling DMA unmap on the first part (with a different length than map)
Signed-off-by: Felix Fietkau <nbd@nbd.name>

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

@@ -61,10 +61,16 @@ mt76_dma_add_buf(struct mt76_dev *dev, struct mt76_queue *q,
 	for (i = 0; i < nbufs; i += 2, buf += 2) {
 		u32 buf0 = buf[0].addr, buf1 = 0;
 
+		if (buf[0].skip_unmap)
+			q->entry[q->head].skip_buf0 = true;
+		q->entry[q->head].skip_buf1 = i == nbufs - 1;
+
 		ctrl = FIELD_PREP(MT_DMA_CTL_SD_LEN0, buf[0].len);
 		if (i < nbufs - 1) {
 			buf1 = buf[1].addr;
 			ctrl |= FIELD_PREP(MT_DMA_CTL_SD_LEN1, buf[1].len);
+			if (buf[1].skip_unmap)
+				q->entry[q->head].skip_buf1 = true;
 		}
 
 		if (i == nbufs - 1)
@@ -107,7 +113,7 @@ mt76_dma_tx_cleanup_idx(struct mt76_dev *dev, struct mt76_queue *q, int idx,
 				 DMA_TO_DEVICE);
 	}
 
-	if (!(ctrl & MT_DMA_CTL_LAST_SEC0)) {
+	if (!e->skip_buf1) {
 		__le32 addr = READ_ONCE(q->desc[idx].buf1);
 		u32 len = FIELD_GET(MT_DMA_CTL_SD_LEN1, ctrl);
 

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

@@ -79,7 +79,8 @@ enum mt76_rxq_id {
 
 struct mt76_queue_buf {
 	dma_addr_t addr;
-	int len;
+	u16 len;
+	bool skip_unmap;
 };
 
 struct mt76_tx_info {
@@ -101,6 +102,7 @@ struct mt76_queue_entry {
 	};
 	enum mt76_txq_id qid;
 	bool skip_buf0:1;
+	bool skip_buf1:1;
 	bool schedule:1;
 	bool done:1;
 };

drivers/net/wireless/mediatek/mt76/mt7615/pci_mac.c

@@ -107,6 +107,7 @@ mt7615_write_fw_txp(struct mt7615_dev *dev, struct mt76_tx_info *tx_info,
 	/* pass partial skb header to fw */
 	tx_info->buf[0].len = MT_TXD_SIZE + sizeof(*txp);
 	tx_info->buf[1].len = MT_CT_PARSE_LEN;
+	tx_info->buf[1].skip_unmap = true;
 	tx_info->nbuf = MT_CT_DMA_BUF_NUM;
 
 	txp->flags = cpu_to_le16(MT_CT_INFO_APPLY_TXD);

drivers/net/wireless/mediatek/mt76/mt7915/mac.c

@@ -715,6 +715,7 @@ int mt7915_tx_prepare_skb(struct mt76_dev *mdev, void *txwi_ptr,
 
 	/* pass partial skb header to fw */
 	tx_info->buf[1].len = MT_CT_PARSE_LEN;
+	tx_info->buf[1].skip_unmap = true;
 	tx_info->nbuf = MT_CT_DMA_BUF_NUM;
 
 	txp->flags = cpu_to_le16(MT_CT_INFO_APPLY_TXD);