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

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Message-ID: <20250516075402.5104a0b6@wsk>
Date: Fri, 16 May 2025 07:54:02 +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,

> 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@...x.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@...x.de

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