Hi Paolo,

On 6/22/25 11:37 AM, Lukasz Majewski wrote:

quoted

This patch provides callbacks for struct net_device_ops for MTIP
L2 switch.

Signed-off-by: Lukasz Majewski <lukma@denx.de>

---
Changes for v13:
- New patch - created by excluding some code from large (i.e. v12
and earlier) MTIP driver
---
 .../net/ethernet/freescale/mtipsw/mtipl2sw.c  | 273
++++++++++++++++++ 1 file changed, 273 insertions(+)

diff --git a/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c

b/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c index
5142f647d939..813cd39d6d56 100644 ---
a/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c +++
b/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c @@ -43,6 +43,15

@@ 
 #include "mtipl2sw.h"
 
+static void swap_buffer(void *bufaddr, int len)
+{
+	int i;
+	unsigned int *buf = bufaddr;
+
+	for (i = 0; i < len; i += 4, buf++)
+		swab32s(buf);
+}
+
 /* Set the last buffer to wrap */
 static void mtip_set_last_buf_to_wrap(struct cbd_t *bdp)
 {

@@ -444,6 +453,128 @@ static void mtip_config_switch(struct

switch_enet_private *fep) fep->hwp + ESW_IMR);
 }
 
+static netdev_tx_t mtip_start_xmit_port(struct sk_buff *skb,
+					struct net_device *dev,
int port) +{
+	struct mtip_ndev_priv *priv = netdev_priv(dev);
+	struct switch_enet_private *fep = priv->fep;
+	unsigned short status;
+	struct cbd_t *bdp;
+	void *bufaddr;
+
+	spin_lock_bh(&fep->hw_lock);
+
+	if (!fep->link[0] && !fep->link[1]) {
+		/* Link is down or autonegotiation is in progress.
*/
+		netif_stop_queue(dev);
+		spin_unlock_bh(&fep->hw_lock);
+		return NETDEV_TX_BUSY;
+	}
+
+	/* Fill in a Tx ring entry */
+	bdp = fep->cur_tx;
+
+	status = bdp->cbd_sc;
+
+	if (status & BD_ENET_TX_READY) {
+		/* All transmit buffers are full. Bail out.
+		 * This should not happen, since dev->tbusy should
be set.
+		 */
+		netif_stop_queue(dev);
+		dev_err(&fep->pdev->dev, "%s: tx queue full!.\n",
dev->name);
+		spin_unlock_bh(&fep->hw_lock);
+		return NETDEV_TX_BUSY;
+	}
+
+	/* Clear all of the status flags */
+	status &= ~BD_ENET_TX_STATS;
+
+	/* Set buffer length and buffer pointer */
+	bufaddr = skb->data;
+	bdp->cbd_datlen = skb->len;
+
+	/* On some FEC implementations data must be aligned on
+	 * 4-byte boundaries. Use bounce buffers to copy data
+	 * and get it aligned.spin
+	 */
+	if ((unsigned long)bufaddr & MTIP_ALIGNMENT) {
+		unsigned int index;
+
+		index = bdp - fep->tx_bd_base;
+		memcpy(fep->tx_bounce[index],
+		       (void *)skb->data, skb->len);
+		bufaddr = fep->tx_bounce[index];
+	}
+
+	if (fep->quirks & FEC_QUIRK_SWAP_FRAME)
+		swap_buffer(bufaddr, skb->len);
+
+	/* Save skb pointer. */
+	fep->tx_skbuff[fep->skb_cur] = skb;
+
+	fep->skb_cur = (fep->skb_cur + 1) & TX_RING_MOD_MASK;
+
+	/* Push the data cache so the CPM does not get stale memory
+	 * data.
+	 */
+	bdp->cbd_bufaddr = dma_map_single(&fep->pdev->dev, bufaddr,
+					  MTIP_SWITCH_TX_FRSIZE,
+					  DMA_TO_DEVICE);
+	if (unlikely(dma_mapping_error(&fep->pdev->dev,
bdp->cbd_bufaddr))) {
+		dev_err(&fep->pdev->dev,
+			"Failed to map descriptor tx buffer\n");
+		dev->stats.tx_errors++;
+		dev->stats.tx_dropped++;
+		dev_kfree_skb_any(skb);
+		goto err;
+	}
+
+	/* Send it on its way.  Tell FEC it's ready, interrupt
when done,
+	 * it's the last BD of the frame, and to put the CRC on
the end.
+	 */
+
+	status |= (BD_ENET_TX_READY | BD_ENET_TX_INTR
+			| BD_ENET_TX_LAST | BD_ENET_TX_TC);
+
+	/* Synchronize all descriptor writes */
+	wmb();
+	bdp->cbd_sc = status;
+
+	netif_trans_update(dev);
+	skb_tx_timestamp(skb);
+
+	/* Trigger transmission start */
+	writel(MCF_ESW_TDAR_X_DES_ACTIVE, fep->hwp + ESW_TDAR);
+
+	dev->stats.tx_bytes += skb->len;
+	/* If this was the last BD in the ring,
+	 * start at the beginning again.
+	 */
+	if (status & BD_ENET_TX_WRAP)
+		bdp = fep->tx_bd_base;
+	else
+		bdp++;
+
+	if (bdp == fep->dirty_tx) {
+		fep->tx_full = 1;
+		netif_stop_queue(dev);  

You may want to stop the queue earlier, i.e. when 75% or the like of
the tx ring is full. Also you can use netif_txq_maybe_stop() - with
txq == netdev_get_tx_queue(dev, 0)

There are two main reasons why the netif queue management is so rugged:

1. Due to simplicity - this driver is not using txq (queues), so I
cannot use APIs using as input argument queues. That is why functions
accepting only struct netdev pointer are used.

2. My feeling is that I would need to use queues abstraction only for
one queue - so this would be extra code overhead. I'm trying to
upstream driver which in fact has very simple internals (i.e. ringbuf
with 16 descriptors for tx/rx).

[...]

quoted

+static void mtip_timeout(struct net_device *dev, unsigned int
txqueue) +{
+	struct mtip_ndev_priv *priv = netdev_priv(dev);
+	struct switch_enet_private *fep = priv->fep;
+	struct cbd_t *bdp;
+	int i;
+
+	dev->stats.tx_errors++;
+
+	if (IS_ENABLED(CONFIG_SWITCH_DEBUG)) {
+		dev_info(&dev->dev, "%s: transmit timed out.\n",
dev->name);
+		dev_info(&dev->dev,
+			 "Ring data: cur_tx %lx%s, dirty_tx %lx
cur_rx: %lx\n",
+			 (unsigned long)fep->cur_tx,
+			 fep->tx_full ? " (full)" : "",
+			 (unsigned long)fep->dirty_tx,
+			 (unsigned long)fep->cur_rx);
+
+		bdp = fep->tx_bd_base;
+		dev_info(&dev->dev, " tx: %u buffers\n",
TX_RING_SIZE);
+		for (i = 0; i < TX_RING_SIZE; i++) {
+			dev_info(&dev->dev, "  %08lx: %04x %04x
%08x\n",
+				 (kernel_ulong_t)bdp, bdp->cbd_sc,
+				 bdp->cbd_datlen,
(int)bdp->cbd_bufaddr);
+			bdp++;
+		}
+
+		bdp = fep->rx_bd_base;
+		dev_info(&dev->dev, " rx: %lu buffers\n",
+			 (unsigned long)RX_RING_SIZE);
+		for (i = 0 ; i < RX_RING_SIZE; i++) {
+			dev_info(&dev->dev, "  %08lx: %04x %04x
%08x\n",
+				 (kernel_ulong_t)bdp,
+				 bdp->cbd_sc, bdp->cbd_datlen,
+				 (int)bdp->cbd_bufaddr);
+			bdp++;
+		}  

Here you are traversing both rings without any lock, which looks race
prone.

I will add  spin_{un}lock_bh(&fep->hw_lock); (this is only code used
for debugging, not production)

/P

Best regards,

Lukasz Majewski

--

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