Re: [net-next v16 06/12] net: mtip: Add net_device_ops functions to the L2 switch driver

[Jakub Kicinski <kuba@kernel.org>]

On Fri, 25 Jul 2025 00:33:12 +0200 Lukasz Majewski wrote:
> +static void swap_buffer(void *bufaddr, int len)
> +{
> +	int i;
> +	unsigned int *buf = bufaddr;
> +

nit: reverse xmas tree

> +	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_ratelimited(&fep->pdev->dev, "%s: tx queue full!.\n",
> +				    dev->name);
> +		spin_unlock(&fep->hw_lock);

As we discussed on previous revision you have many to one mapping
of netdevs to queues. I think the warning should only be printed
if the drivers is in "single netdev" mode. Otherwise it _will_
trigger.

BTW you should put the print after the unlock, console writes are slow.

> +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)) {

why are you hiding the debug info under a CONFIG_ ? 
(which BTW appears not to be defined at all)
Seems useful to know the state of the HW when the queue hung.
You can use a DO_ONCE() if you want to avoid spamming logs

> +	/* Set buffer length and buffer pointer */
> +	bufaddr = skb->data;

You should call skb_cow_data() if you want to write to the skb data.

> +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++;

timeouts are already counted by the stack, I think the statistic
is exposed per-queue in sysfs

> +		spin_lock_bh(&fep->hw_lock);
> +		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++;
> +		}
> +		spin_unlock_bh(&fep->hw_lock);