Re: [net-next v11 4/7] net: mtip: The L2 switch driver for imx287

Lukasz Majewski
2025-05-06T13:29:54Z

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Hi Paolo,

> On 5/4/25 4:55 PM, Lukasz Majewski wrote:
> > + /* This does 16 byte alignment, exactly what we
> > need.
> > + * The packet length includes FCS, but we don't
> > want to
> > + * include that when passing upstream as it messes
> > up
> > + * bridging applications.
> > + */
> > + skb = netdev_alloc_skb(pndev, pkt_len +
> > NET_IP_ALIGN);
> > + if (unlikely(!skb)) {
> > + dev_dbg(&fep->pdev->dev,
> > + "%s: Memory squeeze, dropping
> > packet.\n",
> > + pndev->name);
> > + pndev->stats.rx_dropped++;
> > + goto err_mem;
> > + } else {
> > + skb_reserve(skb, NET_IP_ALIGN);
> > + skb_put(skb, pkt_len); /* Make room */
> > + skb_copy_to_linear_data(skb, data,
> > pkt_len);
> > + skb->protocol = eth_type_trans(skb, pndev);
> > + napi_gro_receive(&fep->napi, skb);
> > + }
> > +
> > + bdp->cbd_bufaddr = dma_map_single(&fep->pdev->dev,
> > data,
> > + bdp->cbd_datlen,
> > + DMA_FROM_DEVICE);
> > + if (unlikely(dma_mapping_error(&fep->pdev->dev,
> > + bdp->cbd_bufaddr)))
> > {
> > + dev_err(&fep->pdev->dev,
> > + "Failed to map descriptor rx
> > buffer\n");
> > + pndev->stats.rx_errors++;
> > + pndev->stats.rx_dropped++;
> > + dev_kfree_skb_any(skb);
> > + goto err_mem;
> > + }
>
> This is doing the mapping and ev. dropping the skb _after_ pushing the
> skb up the stack, you must attempt the mapping first.
>
> > +static void mtip_free_buffers(struct net_device *dev)
> > +{
> > + struct mtip_ndev_priv *priv = netdev_priv(dev);
> > + struct switch_enet_private *fep = priv->fep;
> > + struct sk_buff *skb;
> > + struct cbd_t *bdp;
> > + int i;
> > +
> > + bdp = fep->rx_bd_base;
> > + for (i = 0; i < RX_RING_SIZE; i++) {
> > + skb = fep->rx_skbuff[i];
> > +
> > + if (bdp->cbd_bufaddr)
> > + dma_unmap_single(&fep->pdev->dev,
> > bdp->cbd_bufaddr,
> > + MTIP_SWITCH_RX_FRSIZE,
> > + DMA_FROM_DEVICE);
> > + if (skb)
> > + dev_kfree_skb(skb);
>
> I suspect that on error paths mtip_free_buffers() can be invoked
> multiple consecutive times with any successful allocation in between:
> skb will be freed twice. Likely you need to clear fep->rx_skbuff[i]
> here.

I don't know what I shall say now.... really...

>
> Side note: this patch is way too big for a proper review: you need to
> break it in multiple smaller ones, introducing the basic features
> separately.
>

This code is a basic version of the driver as discussed on March with
the community (Andrew).

It provides the basic functionality - like separate ports support and
then, if required, configures the IP block to perform L2 switching in
HW.

> Cheers,
>
> Paolo
>

Best regards,

Lukasz Majewski

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