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

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Message-ID: <20250725155440.GF1367887@horms.kernel.org>
Date: Fri, 25 Jul 2025 16:54:40 +0100
From: Simon Horman <horms@...nel.org>
To: Lukasz Majewski <lukma@...x.de>
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

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()

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;
> +}

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