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

Lukasz Majewski
2025-05-13T05:34:05Z

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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.

I've double check it - the code seems to be correct.

This code is a part of mtip_switch_rx() function, which handles
receiving data.

First, on probe, the initial dma memory is mapped for MTIP received
data.

When we receive data, it is processed and afterwards it is "pushed" up
to the network stack.

As a last step we do map memory for next, incoming data and leave the
function.

Hence, IMHO, the order is OK and this part shall be left as is.

>
> > +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.

+1 - I will add it with v12.

>
> 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.
>
> Cheers,
>
> Paolo
>

Best regards,

Lukasz Majewski

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