Re: [net-next,v22,4/7] net: mtip: Add net_device_ops functions to the L2 switch driver

[Jakub Kicinski <kuba@kernel.org>]

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net: mtip: Add net_device_ops functions to the L2 switch driver

This patch adds net_device_ops callbacks for the MTIP L2 switch driver,
including transmit, multicast configuration, MAC address handling, and
timeout recovery functions.

> diff --git a/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c b/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c
> --- a/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c
> +++ b/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c

[ ... ]

> +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;
> +	unsigned int index;
> +	struct cbd_t *bdp;
> +	void *bufaddr;
> +
> +	spin_lock_bh(&fep->hw_lock);

[ ... ]

> +	/* Save skb pointer. */
> +	fep->tx_skbuff[index] = skb;

mtip_start_xmit_port() stores sk_buffs in fep->tx_skbuff[index] and creates
DMA mappings, but mtip_switch_tx() which should complete TX operations is
empty:

static void mtip_switch_tx(struct switch_enet_private *fep)
{
}

The NAPI poll handler mtip_rx_napi() calls mtip_switch_tx() to reclaim
transmitted buffers. Since it does nothing, won't every transmitted packet
leak the skb and DMA mapping? Also, dirty_tx is never advanced, so the TX
ring will fill (cur_tx == dirty_tx) and stop accepting packets.

jakub: maybe add a TODO comment transiently here, since later patch implements
       the cleanup?

> +static void mtip_timeout(struct net_device *dev, unsigned int txqueue)
> +{
> +	struct mtip_ndev_priv *priv = netdev_priv(dev);
> +
> +	dev->stats.tx_errors++;

Jakub Kicinski noted in v16 review that tx_errors are already counted by
the network stack, and the statistic is exposed per-queue in sysfs. Does
incrementing tx_errors here double-count timeout events?

https://lore.kernel.org/all/20250725151618.0bc84bdb@kernel.org/

> +	DO_ONCE(mtip_print_hw_state, dev);
> +
> +	schedule_work(&priv->tx_timeout_work);
> +}