Re: [net-next,v20,7/7] net: mtip: Extend the L2 switch driver for imx287 with bridge operations

[Jakub Kicinski <kuba@kernel.org>]

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---
net: mtip: Extend the L2 switch driver for imx287 with bridge operations

This patch adds bridge operations support to the MTIP L2 switch driver,
enabling hardware offloading for packet switching when a bridge is
created on the switch interfaces.

> diff --git a/drivers/net/ethernet/freescale/mtipsw/mtipl2sw_br.c b/drivers/net/ethernet/freescale/mtipsw/mtipl2sw_br.c
> new file mode 100644
> index 000000000000..f961b9cc4e6a
> --- /dev/null
> +++ b/drivers/net/ethernet/freescale/mtipsw/mtipl2sw_br.c

[ ... ]

> +static int mtip_ndev_port_link(struct net_device *ndev,
> +			       struct net_device *br_ndev,
> +			       struct netlink_ext_ack *extack)
> +{
> +	struct mtip_ndev_priv *priv = netdev_priv(ndev), *other_priv;
> +	struct switch_enet_private *fep = priv->fep;
> +	struct net_device *other_ndev;
> +	int err;
> +
> +	/* Check if one port of MTIP switch is already bridged */
> +	if (fep->br_members && !fep->br_offload) {
> +		/* Get the second bridge ndev */
> +		other_ndev = fep->ndev[fep->br_members - 1];
> +		other_priv = netdev_priv(other_ndev);
> +		if (other_priv->master_dev != br_ndev) {
> +			NL_SET_ERR_MSG_MOD(extack,
> +					   "L2 offloading only possible for the same bridge!");
> +			return notifier_from_errno(-EOPNOTSUPP);
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Should this return -EOPNOTSUPP instead of notifier_from_errno(-EOPNOTSUPP)?
The caller mtip_netdevice_event() already wraps the return value with
notifier_from_errno(ret), so double-wrapping corrupts the return value.

Looking at similar drivers like cpsw_new.c (cpsw_netdevice_port_link),
the pattern is to return raw errno values here and let the event handler
do the conversion.

> +		}
> +
> +		fep->br_offload = 1;
> +		mtip_switch_dis_port_separation(fep);
> +		mtip_clear_atable(fep);
> +	}
> +
> +	if (!priv->master_dev)
> +		priv->master_dev = br_ndev;
> +
> +	fep->br_members |= BIT(priv->portnum - 1);
> +
> +	err = switchdev_bridge_port_offload(ndev, ndev, NULL, NULL, NULL,
> +					    false, extack);
> +	if (err) {
> +		dev_err(&ndev->dev, "can't offload bridge port %s [err: %d]\n",
> +			ndev->name, err);
> +		return err;
> +	}

If switchdev_bridge_port_offload() fails, the state changes made earlier
in the function (br_offload, br_members, master_dev, and the hardware
configuration via mtip_switch_dis_port_separation and mtip_clear_atable)
are not rolled back.

Looking at cpsw_new.c for reference, it modifies br_members after the
switchdev call succeeds, avoiding the need for rollback. Could the state
updates here be reordered to happen after switchdev_bridge_port_offload()
returns successfully?

[ ... ]

> +static int mtip_netdevice_event(struct notifier_block *unused,
> +				unsigned long event, void *ptr)
> +{

[ ... ]

> +	return notifier_from_errno(ret);
> +}

[ ... ]