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

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Message-ID: <20250506130438.149c137e@wsk>
Date: Tue, 6 May 2025 13:04:38 +0200
From: Lukasz Majewski <lukma@...x.de>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, davem@...emloft.net, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>, Sascha Hauer
 <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, Richard Cochran
 <richardcochran@...il.com>, netdev@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, Stefan Wahren
 <wahrenst@....net>, Simon Horman <horms@...nel.org>, Andrew Lunn
 <andrew@...n.ch>
Subject: Re: [net-next v11 4/7] net: mtip: The L2 switch driver for imx287

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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