Re: [net-next v13 05/11] net: mtip: Add net_device_ops functions to the L2 switch driver

[Paolo Abeni <pabeni@redhat.com>]

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

[...]
> +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.

/P