net/dsa/master.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * Handling of a master device, switching frames via its switch fabric CPU port
  *
  * Copyright (c) 2017 Savoir-faire Linux Inc.
  *	Vivien Didelot <vivien.didelot@savoirfairelinux.com>
  */

 #include "dsa_priv.h"

 static int dsa_master_get_regs_len(struct net_device *dev)
 {
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
 	struct dsa_switch *ds = cpu_dp->ds;
 	int port = cpu_dp->index;
 	int ret = 0;
 	int len;

 	if (ops->get_regs_len) {
 		len = ops->get_regs_len(dev);
 		if (len < 0)
 			return len;
 		ret += len;
 	}

 	ret += sizeof(struct ethtool_drvinfo);
 	ret += sizeof(struct ethtool_regs);

 	if (ds->ops->get_regs_len) {
 		len = ds->ops->get_regs_len(ds, port);
 		if (len < 0)
 			return len;
 		ret += len;
 	}

 	return ret;
 }

 static void dsa_master_get_regs(struct net_device *dev,
 				struct ethtool_regs *regs, void *data)
 {
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
 	struct dsa_switch *ds = cpu_dp->ds;
 	struct ethtool_drvinfo *cpu_info;
 	struct ethtool_regs *cpu_regs;
 	int port = cpu_dp->index;
 	int len;

 	if (ops->get_regs_len && ops->get_regs) {
 		len = ops->get_regs_len(dev);
 		if (len < 0)
 			return;
 		regs->len = len;
 		ops->get_regs(dev, regs, data);
 		data += regs->len;
 	}

 	cpu_info = (struct ethtool_drvinfo *)data;
 	strlcpy(cpu_info->driver, "dsa", sizeof(cpu_info->driver));
 	data += sizeof(*cpu_info);
 	cpu_regs = (struct ethtool_regs *)data;
 	data += sizeof(*cpu_regs);

 	if (ds->ops->get_regs_len && ds->ops->get_regs) {
 		len = ds->ops->get_regs_len(ds, port);
 		if (len < 0)
 			return;
 		cpu_regs->len = len;
 		ds->ops->get_regs(ds, port, cpu_regs, data);
 	}
 }

 static void dsa_master_get_ethtool_stats(struct net_device *dev,
 					 struct ethtool_stats *stats,
 					 uint64_t *data)
 {
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
 	struct dsa_switch *ds = cpu_dp->ds;
 	int port = cpu_dp->index;
 	int count = 0;

 	if (ops->get_sset_count && ops->get_ethtool_stats) {
 		count = ops->get_sset_count(dev, ETH_SS_STATS);
 		ops->get_ethtool_stats(dev, stats, data);
 	}

 	if (ds->ops->get_ethtool_stats)
 		ds->ops->get_ethtool_stats(ds, port, data + count);
 }

 static void dsa_master_get_ethtool_phy_stats(struct net_device *dev,
 					     struct ethtool_stats *stats,
 					     uint64_t *data)
 {
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
 	struct dsa_switch *ds = cpu_dp->ds;
 	int port = cpu_dp->index;
 	int count = 0;

 	if (dev->phydev && !ops->get_ethtool_phy_stats) {
 		count = phy_ethtool_get_sset_count(dev->phydev);
 		if (count >= 0)
 			phy_ethtool_get_stats(dev->phydev, stats, data);
 	} else if (ops->get_sset_count && ops->get_ethtool_phy_stats) {
 		count = ops->get_sset_count(dev, ETH_SS_PHY_STATS);
 		ops->get_ethtool_phy_stats(dev, stats, data);
 	}

 	if (count < 0)
 		count = 0;

 	if (ds->ops->get_ethtool_phy_stats)
 		ds->ops->get_ethtool_phy_stats(ds, port, data + count);
 }

 static int dsa_master_get_sset_count(struct net_device *dev, int sset)
 {
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
 	struct dsa_switch *ds = cpu_dp->ds;
 	int count = 0;

 	if (sset == ETH_SS_PHY_STATS && dev->phydev &&
 	    !ops->get_ethtool_phy_stats)
 		count = phy_ethtool_get_sset_count(dev->phydev);
 	else if (ops->get_sset_count)
 		count = ops->get_sset_count(dev, sset);

 	if (count < 0)
 		count = 0;

 	if (ds->ops->get_sset_count)
 		count += ds->ops->get_sset_count(ds, cpu_dp->index, sset);

 	return count;
 }

 static void dsa_master_get_strings(struct net_device *dev, uint32_t stringset,
 				   uint8_t *data)
 {
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
 	struct dsa_switch *ds = cpu_dp->ds;
 	int port = cpu_dp->index;
 	int len = ETH_GSTRING_LEN;
 	int mcount = 0, count, i;
 	uint8_t pfx[4];
 	uint8_t *ndata;

 	snprintf(pfx, sizeof(pfx), "p%.2d", port);
 	/* We do not want to be NULL-terminated, since this is a prefix */
 	pfx[sizeof(pfx) - 1] = '_';

 	if (stringset == ETH_SS_PHY_STATS && dev->phydev &&
 	    !ops->get_ethtool_phy_stats) {
 		mcount = phy_ethtool_get_sset_count(dev->phydev);
 		if (mcount < 0)
 			mcount = 0;
 		else
 			phy_ethtool_get_strings(dev->phydev, data);
 	} else if (ops->get_sset_count && ops->get_strings) {
 		mcount = ops->get_sset_count(dev, stringset);
 		if (mcount < 0)
 			mcount = 0;
 		ops->get_strings(dev, stringset, data);
 	}

 	if (ds->ops->get_strings) {
 		ndata = data + mcount * len;
 		/* This function copies ETH_GSTRINGS_LEN bytes, we will mangle
 		 * the output after to prepend our CPU port prefix we
 		 * constructed earlier
 		 */
 		ds->ops->get_strings(ds, port, stringset, ndata);
 		count = ds->ops->get_sset_count(ds, port, stringset);
 		if (count < 0)
 			return;
 		for (i = 0; i < count; i++) {
 			memmove(ndata + (i * len + sizeof(pfx)),
 				ndata + i * len, len - sizeof(pfx));
 			memcpy(ndata + i * len, pfx, sizeof(pfx));
 		}
 	}
 }

 static int dsa_master_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 {
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	struct dsa_switch *ds = cpu_dp->ds;
 	struct dsa_switch_tree *dst;
 	int err = -EOPNOTSUPP;
 	struct dsa_port *dp;

 	dst = ds->dst;

 	switch (cmd) {
 	case SIOCGHWTSTAMP:
 	case SIOCSHWTSTAMP:
 		/* Deny PTP operations on master if there is at least one
 		 * switch in the tree that is PTP capable.
 		 */
 		list_for_each_entry(dp, &dst->ports, list)
 			if (dp->ds->ops->port_hwtstamp_get ||
 			    dp->ds->ops->port_hwtstamp_set)
 				return -EBUSY;
 		break;
 	}

 	if (dev->netdev_ops->ndo_eth_ioctl)
 		err = dev->netdev_ops->ndo_eth_ioctl(dev, ifr, cmd);

 	return err;
 }

 static const struct dsa_netdevice_ops dsa_netdev_ops = {
 	.ndo_eth_ioctl = dsa_master_ioctl,
 };

 static int dsa_master_ethtool_setup(struct net_device *dev)
 {
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	struct dsa_switch *ds = cpu_dp->ds;
 	struct ethtool_ops *ops;

 	ops = devm_kzalloc(ds->dev, sizeof(*ops), GFP_KERNEL);
 	if (!ops)
 		return -ENOMEM;

 	cpu_dp->orig_ethtool_ops = dev->ethtool_ops;
 	if (cpu_dp->orig_ethtool_ops)
 		memcpy(ops, cpu_dp->orig_ethtool_ops, sizeof(*ops));

 	ops->get_regs_len = dsa_master_get_regs_len;
 	ops->get_regs = dsa_master_get_regs;
 	ops->get_sset_count = dsa_master_get_sset_count;
 	ops->get_ethtool_stats = dsa_master_get_ethtool_stats;
 	ops->get_strings = dsa_master_get_strings;
 	ops->get_ethtool_phy_stats = dsa_master_get_ethtool_phy_stats;

 	dev->ethtool_ops = ops;

 	return 0;
 }

 static void dsa_master_ethtool_teardown(struct net_device *dev)
 {
 	struct dsa_port *cpu_dp = dev->dsa_ptr;

 	dev->ethtool_ops = cpu_dp->orig_ethtool_ops;
 	cpu_dp->orig_ethtool_ops = NULL;
 }

 static void dsa_netdev_ops_set(struct net_device *dev,
 			       const struct dsa_netdevice_ops *ops)
 {
 	dev->dsa_ptr->netdev_ops = ops;
 }

 static void dsa_master_set_promiscuity(struct net_device *dev, int inc)
 {
 	const struct dsa_device_ops *ops = dev->dsa_ptr->tag_ops;

 	if (!ops->promisc_on_master)
 		return;

 	rtnl_lock();
 	dev_set_promiscuity(dev, inc);
 	rtnl_unlock();
 }

 static ssize_t tagging_show(struct device *d, struct device_attribute *attr,
 			    char *buf)
 {
 	struct net_device *dev = to_net_dev(d);
 	struct dsa_port *cpu_dp = dev->dsa_ptr;

 	return sprintf(buf, "%s\n",
 		       dsa_tag_protocol_to_str(cpu_dp->tag_ops));
 }

 static ssize_t tagging_store(struct device *d, struct device_attribute *attr,
 			     const char *buf, size_t count)
 {
 	const struct dsa_device_ops *new_tag_ops, *old_tag_ops;
 	struct net_device *dev = to_net_dev(d);
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	int err;

 	old_tag_ops = cpu_dp->tag_ops;
 	new_tag_ops = dsa_find_tagger_by_name(buf);
 	/* Bad tagger name, or module is not loaded? */
 	if (IS_ERR(new_tag_ops))
 		return PTR_ERR(new_tag_ops);

 	if (new_tag_ops == old_tag_ops)
 		/* Drop the temporarily held duplicate reference, since
 		 * the DSA switch tree uses this tagger.
 		 */
 		goto out;

 	err = dsa_tree_change_tag_proto(cpu_dp->ds->dst, dev, new_tag_ops,
 					old_tag_ops);
 	if (err) {
 		/* On failure the old tagger is restored, so we don't need the
 		 * driver for the new one.
 		 */
 		dsa_tag_driver_put(new_tag_ops);
 		return err;
 	}

 	/* On success we no longer need the module for the old tagging protocol
 	 */
 out:
 	dsa_tag_driver_put(old_tag_ops);
 	return count;
 }
 static DEVICE_ATTR_RW(tagging);

 static struct attribute *dsa_slave_attrs[] = {
 	&dev_attr_tagging.attr,
 	NULL
 };

 static const struct attribute_group dsa_group = {
 	.name	= "dsa",
 	.attrs	= dsa_slave_attrs,
 };

 static void dsa_master_reset_mtu(struct net_device *dev)
 {
 	int err;

 	rtnl_lock();
 	err = dev_set_mtu(dev, ETH_DATA_LEN);
 	if (err)
 		netdev_dbg(dev,
 			   "Unable to reset MTU to exclude DSA overheads\n");
 	rtnl_unlock();
 }

 static struct lock_class_key dsa_master_addr_list_lock_key;

 int dsa_master_setup(struct net_device *dev, struct dsa_port *cpu_dp)
 {
 	const struct dsa_device_ops *tag_ops = cpu_dp->tag_ops;
 	struct dsa_switch *ds = cpu_dp->ds;
 	struct device_link *consumer_link;
 	int mtu, ret;

 	mtu = ETH_DATA_LEN + dsa_tag_protocol_overhead(tag_ops);

 	/* The DSA master must use SET_NETDEV_DEV for this to work. */
 	consumer_link = device_link_add(ds->dev, dev->dev.parent,
 					DL_FLAG_AUTOREMOVE_CONSUMER);
 	if (!consumer_link)
 		netdev_err(dev,
 			   "Failed to create a device link to DSA switch %s\n",
 			   dev_name(ds->dev));

 	rtnl_lock();
 	ret = dev_set_mtu(dev, mtu);
 	rtnl_unlock();
 	if (ret)
 		netdev_warn(dev, "error %d setting MTU to %d to include DSA overhead\n",
 			    ret, mtu);

 	/* If we use a tagging format that doesn't have an ethertype
 	 * field, make sure that all packets from this point on get
 	 * sent to the tag format's receive function.
 	 */
 	wmb();

 	dev->dsa_ptr = cpu_dp;
 	lockdep_set_class(&dev->addr_list_lock,
 			  &dsa_master_addr_list_lock_key);

 	dsa_master_set_promiscuity(dev, 1);

 	ret = dsa_master_ethtool_setup(dev);
 	if (ret)
 		goto out_err_reset_promisc;

 	dsa_netdev_ops_set(dev, &dsa_netdev_ops);

 	ret = sysfs_create_group(&dev->dev.kobj, &dsa_group);
 	if (ret)
 		goto out_err_ndo_teardown;

 	return ret;

 out_err_ndo_teardown:
 	dsa_netdev_ops_set(dev, NULL);
 	dsa_master_ethtool_teardown(dev);
 out_err_reset_promisc:
 	dsa_master_set_promiscuity(dev, -1);
 	return ret;
 }

 void dsa_master_teardown(struct net_device *dev)
 {
 	sysfs_remove_group(&dev->dev.kobj, &dsa_group);
 	dsa_netdev_ops_set(dev, NULL);
 	dsa_master_ethtool_teardown(dev);
 	dsa_master_reset_mtu(dev);
 	dsa_master_set_promiscuity(dev, -1);

 	dev->dsa_ptr = NULL;

 	/* If we used a tagging format that doesn't have an ethertype
 	 * field, make sure that all packets from this point get sent
 	 * without the tag and go through the regular receive path.
 	 */
 	wmb();
 }
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* Handling of a master device, switching frames via its switch fabric CPU port
	*
	* Copyright (c) 2017 Savoir-faire Linux Inc.
	* Vivien Didelot <vivien.didelot@savoirfairelinux.com>
	*/

	#include "dsa_priv.h"

	static int dsa_master_get_regs_len(struct net_device *dev)
	{
	struct dsa_port *cpu_dp = dev->dsa_ptr;
	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
	struct dsa_switch *ds = cpu_dp->ds;
	int port = cpu_dp->index;
	int ret = 0;
	int len;

	if (ops->get_regs_len) {
	len = ops->get_regs_len(dev);
	if (len < 0)
	return len;
	ret += len;
	}

	ret += sizeof(struct ethtool_drvinfo);
	ret += sizeof(struct ethtool_regs);

	if (ds->ops->get_regs_len) {
	len = ds->ops->get_regs_len(ds, port);
	if (len < 0)
	return len;
	ret += len;
	}

	return ret;
	}

	static void dsa_master_get_regs(struct net_device *dev,
	struct ethtool_regs regs, void data)
	{
	struct dsa_port *cpu_dp = dev->dsa_ptr;
	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
	struct dsa_switch *ds = cpu_dp->ds;
	struct ethtool_drvinfo *cpu_info;
	struct ethtool_regs *cpu_regs;
	int port = cpu_dp->index;
	int len;

	if (ops->get_regs_len && ops->get_regs) {
	len = ops->get_regs_len(dev);
	if (len < 0)
	return;
	regs->len = len;
	ops->get_regs(dev, regs, data);
	data += regs->len;
	}

	cpu_info = (struct ethtool_drvinfo *)data;
	strlcpy(cpu_info->driver, "dsa", sizeof(cpu_info->driver));
	data += sizeof(*cpu_info);
	cpu_regs = (struct ethtool_regs *)data;
	data += sizeof(*cpu_regs);

	if (ds->ops->get_regs_len && ds->ops->get_regs) {
	len = ds->ops->get_regs_len(ds, port);
	if (len < 0)
	return;
	cpu_regs->len = len;
	ds->ops->get_regs(ds, port, cpu_regs, data);
	}
	}

	static void dsa_master_get_ethtool_stats(struct net_device *dev,
	struct ethtool_stats *stats,
	uint64_t *data)
	{
	struct dsa_port *cpu_dp = dev->dsa_ptr;
	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
	struct dsa_switch *ds = cpu_dp->ds;
	int port = cpu_dp->index;
	int count = 0;

	if (ops->get_sset_count && ops->get_ethtool_stats) {
	count = ops->get_sset_count(dev, ETH_SS_STATS);
	ops->get_ethtool_stats(dev, stats, data);
	}

	if (ds->ops->get_ethtool_stats)
	ds->ops->get_ethtool_stats(ds, port, data + count);
	}

	static void dsa_master_get_ethtool_phy_stats(struct net_device *dev,
	struct ethtool_stats *stats,
	uint64_t *data)
	{
	struct dsa_port *cpu_dp = dev->dsa_ptr;
	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
	struct dsa_switch *ds = cpu_dp->ds;
	int port = cpu_dp->index;
	int count = 0;

	if (dev->phydev && !ops->get_ethtool_phy_stats) {
	count = phy_ethtool_get_sset_count(dev->phydev);
	if (count >= 0)
	phy_ethtool_get_stats(dev->phydev, stats, data);
	} else if (ops->get_sset_count && ops->get_ethtool_phy_stats) {
	count = ops->get_sset_count(dev, ETH_SS_PHY_STATS);
	ops->get_ethtool_phy_stats(dev, stats, data);
	}

	if (count < 0)
	count = 0;

	if (ds->ops->get_ethtool_phy_stats)
	ds->ops->get_ethtool_phy_stats(ds, port, data + count);
	}

	static int dsa_master_get_sset_count(struct net_device *dev, int sset)
	{
	struct dsa_port *cpu_dp = dev->dsa_ptr;
	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
	struct dsa_switch *ds = cpu_dp->ds;
	int count = 0;

	if (sset == ETH_SS_PHY_STATS && dev->phydev &&
	!ops->get_ethtool_phy_stats)
	count = phy_ethtool_get_sset_count(dev->phydev);
	else if (ops->get_sset_count)
	count = ops->get_sset_count(dev, sset);

	if (count < 0)
	count = 0;

	if (ds->ops->get_sset_count)
	count += ds->ops->get_sset_count(ds, cpu_dp->index, sset);

	return count;
	}

	static void dsa_master_get_strings(struct net_device *dev, uint32_t stringset,
	uint8_t *data)
	{
	struct dsa_port *cpu_dp = dev->dsa_ptr;
	const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops;
	struct dsa_switch *ds = cpu_dp->ds;
	int port = cpu_dp->index;
	int len = ETH_GSTRING_LEN;
	int mcount = 0, count, i;
	uint8_t pfx[4];
	uint8_t *ndata;

	snprintf(pfx, sizeof(pfx), "p%.2d", port);
	/* We do not want to be NULL-terminated, since this is a prefix */
	pfx[sizeof(pfx) - 1] = '_';

	if (stringset == ETH_SS_PHY_STATS && dev->phydev &&
	!ops->get_ethtool_phy_stats) {
	mcount = phy_ethtool_get_sset_count(dev->phydev);
	if (mcount < 0)
	mcount = 0;
	else
	phy_ethtool_get_strings(dev->phydev, data);
	} else if (ops->get_sset_count && ops->get_strings) {
	mcount = ops->get_sset_count(dev, stringset);
	if (mcount < 0)
	mcount = 0;
	ops->get_strings(dev, stringset, data);
	}

	if (ds->ops->get_strings) {
	ndata = data + mcount * len;
	/* This function copies ETH_GSTRINGS_LEN bytes, we will mangle
	* the output after to prepend our CPU port prefix we
	* constructed earlier
	*/
	ds->ops->get_strings(ds, port, stringset, ndata);
	count = ds->ops->get_sset_count(ds, port, stringset);
	if (count < 0)
	return;
	for (i = 0; i < count; i++) {
	memmove(ndata + (i * len + sizeof(pfx)),
	ndata + i * len, len - sizeof(pfx));
	memcpy(ndata + i * len, pfx, sizeof(pfx));
	}
	}
	}

	static int dsa_master_ioctl(struct net_device dev, struct ifreq ifr, int cmd)
	{
	struct dsa_port *cpu_dp = dev->dsa_ptr;
	struct dsa_switch *ds = cpu_dp->ds;
	struct dsa_switch_tree *dst;
	int err = -EOPNOTSUPP;
	struct dsa_port *dp;

	dst = ds->dst;

	switch (cmd) {
	case SIOCGHWTSTAMP:
	case SIOCSHWTSTAMP:
	/* Deny PTP operations on master if there is at least one
	* switch in the tree that is PTP capable.
	*/
	list_for_each_entry(dp, &dst->ports, list)
	if (dp->ds->ops->port_hwtstamp_get \|\|
	dp->ds->ops->port_hwtstamp_set)
	return -EBUSY;
	break;
	}

	if (dev->netdev_ops->ndo_eth_ioctl)
	err = dev->netdev_ops->ndo_eth_ioctl(dev, ifr, cmd);

	return err;
	}

	static const struct dsa_netdevice_ops dsa_netdev_ops = {
	.ndo_eth_ioctl = dsa_master_ioctl,
	};

	static int dsa_master_ethtool_setup(struct net_device *dev)
	{
	struct dsa_port *cpu_dp = dev->dsa_ptr;
	struct dsa_switch *ds = cpu_dp->ds;
	struct ethtool_ops *ops;

	ops = devm_kzalloc(ds->dev, sizeof(*ops), GFP_KERNEL);
	if (!ops)
	return -ENOMEM;

	cpu_dp->orig_ethtool_ops = dev->ethtool_ops;
	if (cpu_dp->orig_ethtool_ops)
	memcpy(ops, cpu_dp->orig_ethtool_ops, sizeof(*ops));

	ops->get_regs_len = dsa_master_get_regs_len;
	ops->get_regs = dsa_master_get_regs;
	ops->get_sset_count = dsa_master_get_sset_count;
	ops->get_ethtool_stats = dsa_master_get_ethtool_stats;
	ops->get_strings = dsa_master_get_strings;
	ops->get_ethtool_phy_stats = dsa_master_get_ethtool_phy_stats;

	dev->ethtool_ops = ops;

	return 0;
	}

	static void dsa_master_ethtool_teardown(struct net_device *dev)
	{
	struct dsa_port *cpu_dp = dev->dsa_ptr;

	dev->ethtool_ops = cpu_dp->orig_ethtool_ops;
	cpu_dp->orig_ethtool_ops = NULL;
	}

	static void dsa_netdev_ops_set(struct net_device *dev,
	const struct dsa_netdevice_ops *ops)
	{
	dev->dsa_ptr->netdev_ops = ops;
	}

	static void dsa_master_set_promiscuity(struct net_device *dev, int inc)
	{
	const struct dsa_device_ops *ops = dev->dsa_ptr->tag_ops;

	if (!ops->promisc_on_master)
	return;

	rtnl_lock();
	dev_set_promiscuity(dev, inc);
	rtnl_unlock();
	}

	static ssize_t tagging_show(struct device d, struct device_attribute attr,
	char *buf)
	{
	struct net_device *dev = to_net_dev(d);
	struct dsa_port *cpu_dp = dev->dsa_ptr;

	return sprintf(buf, "%s\n",
	dsa_tag_protocol_to_str(cpu_dp->tag_ops));
	}

	static ssize_t tagging_store(struct device d, struct device_attribute attr,
	const char *buf, size_t count)
	{
	const struct dsa_device_ops new_tag_ops, old_tag_ops;
	struct net_device *dev = to_net_dev(d);
	struct dsa_port *cpu_dp = dev->dsa_ptr;
	int err;

	old_tag_ops = cpu_dp->tag_ops;
	new_tag_ops = dsa_find_tagger_by_name(buf);
	/* Bad tagger name, or module is not loaded? */
	if (IS_ERR(new_tag_ops))
	return PTR_ERR(new_tag_ops);

	if (new_tag_ops == old_tag_ops)
	/* Drop the temporarily held duplicate reference, since
	* the DSA switch tree uses this tagger.
	*/
	goto out;

	err = dsa_tree_change_tag_proto(cpu_dp->ds->dst, dev, new_tag_ops,
	old_tag_ops);
	if (err) {
	/* On failure the old tagger is restored, so we don't need the
	* driver for the new one.
	*/
	dsa_tag_driver_put(new_tag_ops);
	return err;
	}

	/* On success we no longer need the module for the old tagging protocol
	*/
	out:
	dsa_tag_driver_put(old_tag_ops);
	return count;
	}
	static DEVICE_ATTR_RW(tagging);

	static struct attribute *dsa_slave_attrs[] = {
	&dev_attr_tagging.attr,
	NULL
	};

	static const struct attribute_group dsa_group = {
	.name = "dsa",
	.attrs = dsa_slave_attrs,
	};

	static void dsa_master_reset_mtu(struct net_device *dev)
	{
	int err;

	rtnl_lock();
	err = dev_set_mtu(dev, ETH_DATA_LEN);
	if (err)
	netdev_dbg(dev,
	"Unable to reset MTU to exclude DSA overheads\n");
	rtnl_unlock();
	}

	static struct lock_class_key dsa_master_addr_list_lock_key;

	int dsa_master_setup(struct net_device dev, struct dsa_port cpu_dp)
	{
	const struct dsa_device_ops *tag_ops = cpu_dp->tag_ops;
	struct dsa_switch *ds = cpu_dp->ds;
	struct device_link *consumer_link;
	int mtu, ret;

	mtu = ETH_DATA_LEN + dsa_tag_protocol_overhead(tag_ops);

	/* The DSA master must use SET_NETDEV_DEV for this to work. */
	consumer_link = device_link_add(ds->dev, dev->dev.parent,
	DL_FLAG_AUTOREMOVE_CONSUMER);
	if (!consumer_link)
	netdev_err(dev,
	"Failed to create a device link to DSA switch %s\n",
	dev_name(ds->dev));

	rtnl_lock();
	ret = dev_set_mtu(dev, mtu);
	rtnl_unlock();
	if (ret)
	netdev_warn(dev, "error %d setting MTU to %d to include DSA overhead\n",
	ret, mtu);

	/* If we use a tagging format that doesn't have an ethertype
	* field, make sure that all packets from this point on get
	* sent to the tag format's receive function.
	*/
	wmb();

	dev->dsa_ptr = cpu_dp;
	lockdep_set_class(&dev->addr_list_lock,
	&dsa_master_addr_list_lock_key);

	dsa_master_set_promiscuity(dev, 1);

	ret = dsa_master_ethtool_setup(dev);
	if (ret)
	goto out_err_reset_promisc;

	dsa_netdev_ops_set(dev, &dsa_netdev_ops);

	ret = sysfs_create_group(&dev->dev.kobj, &dsa_group);
	if (ret)
	goto out_err_ndo_teardown;

	return ret;

	out_err_ndo_teardown:
	dsa_netdev_ops_set(dev, NULL);
	dsa_master_ethtool_teardown(dev);
	out_err_reset_promisc:
	dsa_master_set_promiscuity(dev, -1);
	return ret;
	}

	void dsa_master_teardown(struct net_device *dev)
	{
	sysfs_remove_group(&dev->dev.kobj, &dsa_group);
	dsa_netdev_ops_set(dev, NULL);
	dsa_master_ethtool_teardown(dev);
	dsa_master_reset_mtu(dev);
	dsa_master_set_promiscuity(dev, -1);

	dev->dsa_ptr = NULL;

	/* If we used a tagging format that doesn't have an ethertype
	* field, make sure that all packets from this point get sent
	* without the tag and go through the regular receive path.
	*/
	wmb();
	}