linux-kernel - Re: [net-next v16 06/12] net: mtip: Add net_device

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Message-ID: <20250725192738.0fffece9@wsk>
Date: Fri, 25 Jul 2025 19:27:38 +0200
From: Lukasz Majewski <lukma@...x.de>
To: Simon Horman <horms@...nel.org>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, davem@...emloft.net, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, 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>
Subject: Re: [net-next v16 06/12] net: mtip: Add net_device_ops functions to
 the L2 switch driver

Hi Simon,

> On Fri, Jul 25, 2025 at 12:33:12AM +0200, Lukasz Majewski wrote:
> > This patch provides callbacks for struct net_device_ops for MTIP
> > L2 switch.
> > 
> > Signed-off-by: Lukasz Majewski <lukma@...x.de>  
> 
> ...
> 
> > +static netdev_tx_t mtip_start_xmit_port(struct sk_buff *skb,
> > +					struct net_device *dev,
> > int port) +{
> > +	struct mtip_ndev_priv *priv = netdev_priv(dev);
> > +	struct switch_enet_private *fep = priv->fep;
> > +	unsigned short status;
> > +	struct cbd_t *bdp;
> > +	void *bufaddr;
> > +
> > +	spin_lock_bh(&fep->hw_lock);
> > +
> > +	if (!fep->link[0] && !fep->link[1]) {
> > +		/* Link is down or autonegotiation is in progress.
> > */
> > +		netif_stop_queue(dev);
> > +		spin_unlock_bh(&fep->hw_lock);
> > +		return NETDEV_TX_BUSY;
> > +	}
> > +
> > +	/* Fill in a Tx ring entry */
> > +	bdp = fep->cur_tx;
> > +	status = bdp->cbd_sc;
> > +
> > +	if (status & BD_ENET_TX_READY) {
> > +		/* All transmit buffers are full. Bail out.
> > +		 * This should not happen, since dev->tbusy should
> > be set.
> > +		 */
> > +		netif_stop_queue(dev);
> > +		dev_err_ratelimited(&fep->pdev->dev, "%s: tx queue
> > full!.\n",
> > +				    dev->name);
> > +		spin_unlock(&fep->hw_lock);  
> 
> Sorry be the one to point out this needle in a haystack,
> but this should be spin_unlock_bh()

I must have overlooked it when working on the code.

Anyway, I need to wait if there are other comments from Jakub or Paolo
- as they had some comments (addressed already by this patch set) for
  previous version.

> 
> Flagged by Smatch.
> 
> > +		return NETDEV_TX_BUSY;
> > +	}
> > +
> > +	/* Clear all of the status flags */
> > +	status &= ~BD_ENET_TX_STATS;
> > +
> > +	/* Set buffer length and buffer pointer */
> > +	bufaddr = skb->data;
> > +	bdp->cbd_datlen = skb->len;
> > +
> > +	/* On some FEC implementations data must be aligned on
> > +	 * 4-byte boundaries. Use bounce buffers to copy data
> > +	 * and get it aligned.spin
> > +	 */
> > +	if ((unsigned long)bufaddr & MTIP_ALIGNMENT) {
> > +		unsigned int index;
> > +
> > +		index = bdp - fep->tx_bd_base;
> > +		memcpy(fep->tx_bounce[index], skb->data, skb->len);
> > +		bufaddr = fep->tx_bounce[index];
> > +	}
> > +
> > +	if (fep->quirks & FEC_QUIRK_SWAP_FRAME)
> > +		swap_buffer(bufaddr, skb->len);
> > +
> > +	/* Push the data cache so the CPM does not get stale memory
> > +	 * data.
> > +	 */
> > +	bdp->cbd_bufaddr = dma_map_single(&fep->pdev->dev, bufaddr,
> > +					  MTIP_SWITCH_TX_FRSIZE,
> > +					  DMA_TO_DEVICE);
> > +	if (unlikely(dma_mapping_error(&fep->pdev->dev,
> > bdp->cbd_bufaddr))) {
> > +		dev_err(&fep->pdev->dev,
> > +			"Failed to map descriptor tx buffer\n");
> > +		dev->stats.tx_dropped++;
> > +		dev_kfree_skb_any(skb);
> > +		goto err;
> > +	}
> > +
> > +	/* Save skb pointer. */
> > +	fep->tx_skbuff[fep->skb_cur] = skb;
> > +	fep->skb_cur = (fep->skb_cur + 1) & TX_RING_MOD_MASK;
> > +
> > +	/* Send it on its way.  Tell FEC it's ready, interrupt
> > when done,
> > +	 * it's the last BD of the frame, and to put the CRC on
> > the end.
> > +	 */
> > +
> > +	status |= (BD_ENET_TX_READY | BD_ENET_TX_INTR |
> > BD_ENET_TX_LAST |
> > +		   BD_ENET_TX_TC);
> > +
> > +	/* Synchronize all descriptor writes */
> > +	wmb();
> > +	bdp->cbd_sc = status;
> > +
> > +	skb_tx_timestamp(skb);
> > +
> > +	/* Trigger transmission start */
> > +	writel(MCF_ESW_TDAR_X_DES_ACTIVE, fep->hwp + ESW_TDAR);
> > +
> > +	dev->stats.tx_bytes += skb->len;
> > +	/* If this was the last BD in the ring,
> > +	 * start at the beginning again.
> > +	 */
> > +	if (status & BD_ENET_TX_WRAP)
> > +		bdp = fep->tx_bd_base;
> > +	else
> > +		bdp++;
> > +
> > +	if (bdp == fep->dirty_tx) {
> > +		fep->tx_full = 1;
> > +		netif_stop_queue(dev);
> > +	}
> > +
> > +	fep->cur_tx = bdp;
> > + err:
> > +	spin_unlock_bh(&fep->hw_lock);
> > +
> > +	return NETDEV_TX_OK;
> > +}  
> 
> ...




Best regards,

Lukasz Majewski

--

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