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

Lukasz Majewski
2025-05-16T05:58:06Z

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Hi Paolo,

> 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.

Is the explanation sufficient?

>
> >
> > > +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
>
> --
>
> DENX Software Engineering GmbH, Managing Director: Erika Unter
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email:
> lukma@denx.de

Best regards,

Lukasz Majewski

--

DENX Software Engineering GmbH, Managing Director: Erika Unter
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de

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