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

[Paolo Abeni <pabeni@redhat.com>]

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.

/P