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

Lukasz Majewski
2025-05-27T10:47:32Z

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Hi Paolo,

> On 5/13/25 7:31 AM, Lukasz Majewski wrote:
> >> 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.
>
> First thing first, I'm sorry for lagging behind. This fell outside my
> radar. Let's keep the conversation on the new patch version, it should
> help me to avoid repeating this mistake.

+1

>
> /P
>

Best regards,

Lukasz Majewski

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