net: rswitch: Add jumbo frames handling for TX

If the driver would like to transmit a jumbo frame like 2KiB or more,
it should be split into multiple queues. In the near future, to support
this, add handling specific descriptor types F{START,MID,END}. However,
such jumbo frames will not happen yet because the maximum MTU size is
still default for now.
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/renesas/rswitch.c

@@ -1632,15 +1632,44 @@ static bool rswitch_ext_desc_set(struct rswitch_device *rdev,
 	return true;
 }
 
+static u8 rswitch_ext_desc_get_die_dt(unsigned int nr_desc, unsigned int index)
+{
+	if (nr_desc == 1)
+		return DT_FSINGLE | DIE;
+	if (index == 0)
+		return DT_FSTART;
+	if (nr_desc - 1 == index)
+		return DT_FEND | DIE;
+	return DT_FMID;
+}
+
+static u16 rswitch_ext_desc_get_len(u8 die_dt, unsigned int orig_len)
+{
+	switch (die_dt & DT_MASK) {
+	case DT_FSINGLE:
+	case DT_FEND:
+		return (orig_len % RSWITCH_DESC_BUF_SIZE) ?: RSWITCH_DESC_BUF_SIZE;
+	case DT_FSTART:
+	case DT_FMID:
+		return RSWITCH_DESC_BUF_SIZE;
+	default:
+		return 0;
+	}
+}
+
 static netdev_tx_t rswitch_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 {
 	struct rswitch_device *rdev = netdev_priv(ndev);
 	struct rswitch_gwca_queue *gq = rdev->tx_queue;
+	dma_addr_t dma_addr, dma_addr_orig;
 	netdev_tx_t ret = NETDEV_TX_OK;
 	struct rswitch_ext_desc *desc;
-	dma_addr_t dma_addr;
+	unsigned int i, nr_desc;
+	u8 die_dt;
+	u16 len;
 
-	if (rswitch_get_num_cur_queues(gq) >= gq->ring_size - 1) {
+	nr_desc = (skb->len - 1) / RSWITCH_DESC_BUF_SIZE + 1;
+	if (rswitch_get_num_cur_queues(gq) >= gq->ring_size - nr_desc) {
 		netif_stop_subqueue(ndev, 0);
 		return NETDEV_TX_BUSY;
 	}
@@ -1648,25 +1677,32 @@ static netdev_tx_t rswitch_start_xmit(struct sk_buff *skb, struct net_device *nd
 	if (skb_put_padto(skb, ETH_ZLEN))
 		return ret;
 
-	dma_addr = dma_map_single(ndev->dev.parent, skb->data, skb->len, DMA_TO_DEVICE);
-	if (dma_mapping_error(ndev->dev.parent, dma_addr))
+	dma_addr_orig = dma_map_single(ndev->dev.parent, skb->data, skb->len, DMA_TO_DEVICE);
+	if (dma_mapping_error(ndev->dev.parent, dma_addr_orig))
 		goto err_kfree;
 
 	gq->skbs[gq->cur] = skb;
-	gq->unmap_addrs[gq->cur] = dma_addr;
-	desc = &gq->tx_ring[gq->cur];
-	if (!rswitch_ext_desc_set(rdev, skb, desc, dma_addr, skb->len, DT_FSINGLE | DIE))
-		goto err_unmap;
+	gq->unmap_addrs[gq->cur] = dma_addr_orig;
+
+	/* DT_FSTART should be set at last. So, this is reverse order. */
+	for (i = nr_desc; i-- > 0; ) {
+		desc = &gq->tx_ring[rswitch_next_queue_index(gq, true, i)];
+		die_dt = rswitch_ext_desc_get_die_dt(nr_desc, i);
+		dma_addr = dma_addr_orig + i * RSWITCH_DESC_BUF_SIZE;
+		len = rswitch_ext_desc_get_len(die_dt, skb->len);
+		if (!rswitch_ext_desc_set(rdev, skb, desc, dma_addr, len, die_dt))
+			goto err_unmap;
+	}
 
 	wmb();	/* gq->cur must be incremented after die_dt was set */
 
-	gq->cur = rswitch_next_queue_index(gq, true, 1);
+	gq->cur = rswitch_next_queue_index(gq, true, nr_desc);
 	rswitch_modify(rdev->addr, GWTRC(gq->index), 0, BIT(gq->index % 32));
 
 	return ret;
 
 err_unmap:
-	dma_unmap_single(ndev->dev.parent, dma_addr, skb->len, DMA_TO_DEVICE);
+	dma_unmap_single(ndev->dev.parent, dma_addr_orig, skb->len, DMA_TO_DEVICE);
 
 err_kfree:
 	dev_kfree_skb_any(skb);