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Date:	Sat,  4 Jun 2016 21:17:07 +0200
From:	Andrew Lunn <andrew@...n.ch>
To:	David Miller <davem@...emloft.net>,
	Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
	Florian Fainelli <f.fainelli@...il.com>
Cc:	netdev <netdev@...r.kernel.org>, Shawn Guo <shawnguo@...nel.org>,
	Andrew Lunn <andrew@...n.ch>
Subject: [PATCHv2 net-next 15/17] net: dsa: Add new binding implementation

The existing DSA binding has a number of limitations and problems. The
main problem is that it cannot represent a switch as a linux device,
hanging off some bus. It is limited to one CPU port. The DSA platform
device is artificial, and does not really represent hardware.

Implement a new binding which can be embedded into any type of node on
a bus to represent one switch device, and its links to other switches.

Signed-off-by: Andrew Lunn <andrew@...n.ch>
Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
---
v2:
* dsa2: Clear cpu port mask in  dsa_cpu_port_unapply()
* dsa2: Only set dsa_port_mask when port successfully configured
* dsa: clear {dsa|cpu}_port_mask on destroy
---
 drivers/net/dsa/mv88e6xxx.c |   7 +
 include/net/dsa.h           |  20 ++
 net/dsa/Makefile            |   2 +-
 net/dsa/dsa.c               |   5 +
 net/dsa/dsa2.c              | 655 ++++++++++++++++++++++++++++++++++++++++++++
 net/dsa/dsa_priv.h          |   2 +-
 net/dsa/slave.c             |   8 +-
 7 files changed, 695 insertions(+), 4 deletions(-)
 create mode 100644 net/dsa/dsa2.c

diff --git a/drivers/net/dsa/mv88e6xxx.c b/drivers/net/dsa/mv88e6xxx.c
index 192b39cbdbcd..ee06055444f9 100644
--- a/drivers/net/dsa/mv88e6xxx.c
+++ b/drivers/net/dsa/mv88e6xxx.c
@@ -3748,6 +3748,12 @@ int mv88e6xxx_probe(struct mdio_device *mdiodev)
 
 	dev_set_drvdata(dev, ds);
 
+	err = dsa_register_switch(ds, mdiodev->dev.of_node);
+	if (err) {
+		mv88e6xxx_mdio_unregister(ps);
+		return err;
+	}
+
 	dev_info(dev, "switch 0x%x probed: %s, revision %u\n",
 		 prod_num, ps->info->name, rev);
 
@@ -3759,6 +3765,7 @@ static void mv88e6xxx_remove(struct mdio_device *mdiodev)
 	struct dsa_switch *ds = dev_get_drvdata(&mdiodev->dev);
 	struct mv88e6xxx_priv_state *ps = ds_to_priv(ds);
 
+	dsa_unregister_switch(ds);
 	put_device(&ps->bus->dev);
 
 	mv88e6xxx_mdio_unregister(ps);
diff --git a/include/net/dsa.h b/include/net/dsa.h
index bd6ecaa0de96..cca7ef230742 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -85,6 +85,17 @@ struct dsa_platform_data {
 struct packet_type;
 
 struct dsa_switch_tree {
+	struct list_head	list;
+
+	/* Tree identifier */
+	u32 tree;
+
+	/* Number of switches attached to this tree */
+	struct kref refcount;
+
+	/* Has this tree been applied to the hardware? */
+	bool applied;
+
 	/*
 	 * Configuration data for the platform device that owns
 	 * this dsa switch tree instance.
@@ -170,9 +181,15 @@ struct dsa_switch {
 #endif
 
 	/*
+	 * The lower device this switch uses to talk to the host
+	 */
+	struct net_device *master_netdev;
+
+	/*
 	 * Slave mii_bus and devices for the individual ports.
 	 */
 	u32			dsa_port_mask;
+	u32			cpu_port_mask;
 	u32			enabled_port_mask;
 	u32			phys_mii_mask;
 	struct dsa_port		ports[DSA_MAX_PORTS];
@@ -361,4 +378,7 @@ static inline bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
 {
 	return dst->rcv != NULL;
 }
+
+void dsa_unregister_switch(struct dsa_switch *ds);
+int dsa_register_switch(struct dsa_switch *ds, struct device_node *np);
 #endif
diff --git a/net/dsa/Makefile b/net/dsa/Makefile
index da06ed1df620..8af4ded70f1c 100644
--- a/net/dsa/Makefile
+++ b/net/dsa/Makefile
@@ -1,6 +1,6 @@
 # the core
 obj-$(CONFIG_NET_DSA) += dsa_core.o
-dsa_core-y += dsa.o slave.o
+dsa_core-y += dsa.o slave.o dsa2.o
 
 # tagging formats
 dsa_core-$(CONFIG_NET_DSA_TAG_BRCM) += tag_brcm.o
diff --git a/net/dsa/dsa.c b/net/dsa/dsa.c
index 6c314f300424..ce3b942dce76 100644
--- a/net/dsa/dsa.c
+++ b/net/dsa/dsa.c
@@ -294,6 +294,7 @@ static int dsa_switch_setup_one(struct dsa_switch *ds, struct device *parent)
 			}
 			dst->cpu_switch = index;
 			dst->cpu_port = i;
+			ds->cpu_port_mask |= 1 << i;
 		} else if (!strcmp(name, "dsa")) {
 			ds->dsa_port_mask |= 1 << i;
 		} else {
@@ -492,6 +493,10 @@ static void dsa_switch_destroy(struct dsa_switch *ds)
 		if (!(dsa_is_cpu_port(ds, port) || dsa_is_dsa_port(ds, port)))
 			continue;
 		dsa_cpu_dsa_destroy(ds->ports[port].dn);
+
+		/* Clearing a bit which is not set does no harm */
+		ds->cpu_port_mask |= ~(1 << port);
+		ds->dsa_port_mask |= ~(1 << port);
 	}
 
 	if (ds->slave_mii_bus && ds->drv->phy_read)
diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
new file mode 100644
index 000000000000..42a0dd0581dc
--- /dev/null
+++ b/net/dsa/dsa2.c
@@ -0,0 +1,655 @@
+/*
+ * net/dsa/dsa2.c - Hardware switch handling, binding version 2
+ * Copyright (c) 2008-2009 Marvell Semiconductor
+ * Copyright (c) 2013 Florian Fainelli <florian@...nwrt.org>
+ * Copyright (c) 2016 Andrew Lunn <andrew@...n.ch>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/rtnetlink.h>
+#include <net/dsa.h>
+#include <linux/of.h>
+#include <linux/of_net.h>
+#include "dsa_priv.h"
+
+static LIST_HEAD(dsa_switch_trees);
+static DEFINE_MUTEX(dsa2_mutex);
+
+static struct dsa_switch_tree *dsa_get_dst(u32 tree)
+{
+	struct dsa_switch_tree *dst;
+
+	list_for_each_entry(dst, &dsa_switch_trees, list)
+		if (dst->tree == tree)
+			return dst;
+	return NULL;
+}
+
+static void dsa_free_dst(struct kref *ref)
+{
+	struct dsa_switch_tree *dst = container_of(ref, struct dsa_switch_tree,
+						   refcount);
+
+	list_del(&dst->list);
+	kfree(dst);
+}
+
+static void dsa_put_dst(struct dsa_switch_tree *dst)
+{
+	kref_put(&dst->refcount, dsa_free_dst);
+}
+
+static struct dsa_switch_tree *dsa_add_dst(u32 tree)
+{
+	struct dsa_switch_tree *dst;
+
+	dst = kzalloc(sizeof(*dst), GFP_KERNEL);
+	if (!dst)
+		return NULL;
+	dst->tree = tree;
+	dst->cpu_switch = -1;
+	INIT_LIST_HEAD(&dst->list);
+	list_add_tail(&dsa_switch_trees, &dst->list);
+	kref_init(&dst->refcount);
+
+	return dst;
+}
+
+static void dsa_dst_add_ds(struct dsa_switch_tree *dst,
+			   struct dsa_switch *ds, u32 index)
+{
+	kref_get(&dst->refcount);
+	dst->ds[index] = ds;
+}
+
+static void dsa_dst_del_ds(struct dsa_switch_tree *dst,
+			   struct dsa_switch *ds, u32 index)
+{
+	dst->ds[index] = NULL;
+	kref_put(&dst->refcount, dsa_free_dst);
+}
+
+static bool dsa_port_is_dsa(struct device_node *port)
+{
+	const char *name;
+
+	name = of_get_property(port, "label", NULL);
+	if (!name)
+		return false;
+
+	if (!strcmp(name, "dsa"))
+		return true;
+
+	return false;
+}
+
+static bool dsa_port_is_cpu(struct device_node *port)
+{
+	const char *name;
+
+	name = of_get_property(port, "label", NULL);
+	if (!name)
+		return false;
+
+	if (!strcmp(name, "cpu"))
+		return true;
+
+	return false;
+}
+
+static bool dsa_ds_find_port(struct dsa_switch *ds,
+			     struct device_node *port)
+{
+	u32 index;
+
+	for (index = 0; index < DSA_MAX_PORTS; index++)
+		if (ds->ports[index].dn == port)
+			return true;
+	return false;
+}
+
+static struct dsa_switch *dsa_dst_find_port(struct dsa_switch_tree *dst,
+					    struct device_node *port)
+{
+	struct dsa_switch *ds;
+	u32 index;
+
+	for (index = 0; index < DSA_MAX_SWITCHES; index++) {
+		ds = dst->ds[index];
+		if (!ds)
+			continue;
+
+		if (dsa_ds_find_port(ds, port))
+			return ds;
+	}
+
+	return NULL;
+}
+
+static int dsa_port_complete(struct dsa_switch_tree *dst,
+			     struct dsa_switch *src_ds,
+			     struct device_node *port,
+			     u32 src_port)
+{
+	struct device_node *link;
+	int index;
+	struct dsa_switch *dst_ds;
+
+	for (index = 0;; index++) {
+		link = of_parse_phandle(port, "link", index);
+		if (!link)
+			break;
+
+		dst_ds = dsa_dst_find_port(dst, link);
+		of_node_put(link);
+
+		if (!dst_ds)
+			return 1;
+
+		src_ds->rtable[dst_ds->index] = src_port;
+	}
+
+	return 0;
+}
+
+/* A switch is complete if all the DSA ports phandles point to ports
+ * known in the tree. A return value of 1 means the tree is not
+ * complete. This is not an error condition. A value of 0 is
+ * success.
+ */
+static int dsa_ds_complete(struct dsa_switch_tree *dst, struct dsa_switch *ds)
+{
+	struct device_node *port;
+	u32 index;
+	int err;
+
+	for (index = 0; index < DSA_MAX_PORTS; index++) {
+		port = ds->ports[index].dn;
+		if (!port)
+			continue;
+
+		if (!dsa_port_is_dsa(port))
+			continue;
+
+		err = dsa_port_complete(dst, ds, port, index);
+		if (err != 0)
+			return err;
+
+		ds->dsa_port_mask |= BIT(index);
+	}
+
+	return 0;
+}
+
+/* A tree is complete if all the DSA ports phandles point to ports
+ * known in the tree. A return value of 1 means the tree is not
+ * complete. This is not an error condition. A value of 0 is
+ * success.
+ */
+static int dsa_dst_complete(struct dsa_switch_tree *dst)
+{
+	struct dsa_switch *ds;
+	u32 index;
+	int err;
+
+	for (index = 0; index < DSA_MAX_SWITCHES; index++) {
+		ds = dst->ds[index];
+		if (!ds)
+			continue;
+
+		err = dsa_ds_complete(dst, ds);
+		if (err != 0)
+			return err;
+	}
+
+	return 0;
+}
+
+static int dsa_dsa_port_apply(struct device_node *port, u32 index,
+			      struct dsa_switch *ds)
+{
+	int err;
+
+	err = dsa_cpu_dsa_setup(ds, ds->dev, port, index);
+	if (err) {
+		dev_warn(ds->dev, "Failed to setup dsa port %d: %d\n",
+			 index, err);
+		return err;
+	}
+
+	return 0;
+}
+
+static void dsa_dsa_port_unapply(struct device_node *port, u32 index,
+				 struct dsa_switch *ds)
+{
+	dsa_cpu_dsa_destroy(port);
+}
+
+static int dsa_cpu_port_apply(struct device_node *port, u32 index,
+			      struct dsa_switch *ds)
+{
+	int err;
+
+	err = dsa_cpu_dsa_setup(ds, ds->dev, port, index);
+	if (err) {
+		dev_warn(ds->dev, "Failed to setup cpu port %d: %d\n",
+			 index, err);
+		return err;
+	}
+
+	ds->cpu_port_mask |= BIT(index);
+
+	return 0;
+}
+
+static void dsa_cpu_port_unapply(struct device_node *port, u32 index,
+				 struct dsa_switch *ds)
+{
+	dsa_cpu_dsa_destroy(port);
+	ds->cpu_port_mask &= ~BIT(index);
+
+}
+
+static int dsa_user_port_apply(struct device_node *port, u32 index,
+			       struct dsa_switch *ds)
+{
+	const char *name;
+	int err;
+
+	name = of_get_property(port, "label", NULL);
+
+	err = dsa_slave_create(ds, ds->dev, index, name);
+	if (err) {
+		dev_warn(ds->dev, "Failed to create slave %d: %d\n",
+			 index, err);
+		return err;
+	}
+
+	return 0;
+}
+
+static void dsa_user_port_unapply(struct device_node *port, u32 index,
+				  struct dsa_switch *ds)
+{
+	if (ds->ports[index].netdev) {
+		dsa_slave_destroy(ds->ports[index].netdev);
+		ds->ports[index].netdev = NULL;
+	}
+}
+
+static int dsa_ds_apply(struct dsa_switch_tree *dst, struct dsa_switch *ds)
+{
+	struct device_node *port;
+	u32 index;
+	int err;
+
+	err = ds->drv->setup(ds);
+	if (err < 0)
+		return err;
+
+	err = ds->drv->set_addr(ds, dst->master_netdev->dev_addr);
+	if (err < 0)
+		return err;
+
+	err = ds->drv->set_addr(ds, dst->master_netdev->dev_addr);
+	if (err < 0)
+		return err;
+
+	for (index = 0; index < DSA_MAX_PORTS; index++) {
+		port = ds->ports[index].dn;
+		if (!port)
+			continue;
+
+		if (dsa_port_is_dsa(port)) {
+			err = dsa_dsa_port_apply(port, index, ds);
+			if (err)
+				return err;
+			continue;
+		}
+
+		if (dsa_port_is_cpu(port)) {
+			err = dsa_cpu_port_apply(port, index, ds);
+			if (err)
+				return err;
+			continue;
+		}
+
+		err = dsa_user_port_apply(port, index, ds);
+		if (err)
+			continue;
+	}
+
+	return 0;
+}
+
+static void dsa_ds_unapply(struct dsa_switch_tree *dst, struct dsa_switch *ds)
+{
+	struct device_node *port;
+	u32 index;
+
+	for (index = 0; index < DSA_MAX_PORTS; index++) {
+		port = ds->ports[index].dn;
+		if (!port)
+			continue;
+
+		if (dsa_port_is_dsa(port)) {
+			dsa_dsa_port_unapply(port, index, ds);
+			continue;
+		}
+
+		if (dsa_port_is_cpu(port)) {
+			dsa_cpu_port_unapply(port, index, ds);
+			continue;
+		}
+
+		dsa_user_port_unapply(port, index, ds);
+	}
+}
+
+static int dsa_dst_apply(struct dsa_switch_tree *dst)
+{
+	struct dsa_switch *ds;
+	u32 index;
+	int err;
+
+	for (index = 0; index < DSA_MAX_SWITCHES; index++) {
+		ds = dst->ds[index];
+		if (!ds)
+			continue;
+
+		err = dsa_ds_apply(dst, ds);
+		if (err)
+			return err;
+	}
+
+	/* 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();
+	dst->master_netdev->dsa_ptr = (void *)dst;
+	dst->applied = true;
+
+	return 0;
+}
+
+static void dsa_dst_unapply(struct dsa_switch_tree *dst)
+{
+	struct dsa_switch *ds;
+	u32 index;
+
+	if (!dst->applied)
+		return;
+
+	dst->master_netdev->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();
+
+	for (index = 0; index < DSA_MAX_SWITCHES; index++) {
+		ds = dst->ds[index];
+		if (!ds)
+			continue;
+
+		dsa_ds_unapply(dst, ds);
+	}
+
+	pr_info("DSA: tree %d unapplied\n", dst->tree);
+	dst->applied = false;
+}
+
+static int dsa_cpu_parse(struct device_node *port, u32 index,
+			 struct dsa_switch_tree *dst,
+			 struct dsa_switch *ds)
+{
+	struct net_device *ethernet_dev;
+	struct device_node *ethernet;
+
+	ethernet = of_parse_phandle(port, "ethernet", 0);
+	if (!ethernet)
+		return -EINVAL;
+
+	ethernet_dev = of_find_net_device_by_node(ethernet);
+	if (!ethernet_dev)
+		return -EPROBE_DEFER;
+
+	if (!ds->master_netdev)
+		ds->master_netdev = ethernet_dev;
+
+	if (!dst->master_netdev)
+		dst->master_netdev = ethernet_dev;
+
+	if (dst->cpu_switch == -1) {
+		dst->cpu_switch = ds->index;
+		dst->cpu_port = index;
+	}
+
+	dst->tag_ops = dsa_resolve_tag_protocol(ds->drv->tag_protocol);
+	if (IS_ERR(dst->tag_ops)) {
+		dev_warn(ds->dev, "No tagger for this switch\n");
+		return PTR_ERR(dst->tag_ops);
+	}
+
+	dst->rcv = dst->tag_ops->rcv;
+
+	return 0;
+}
+
+static int dsa_ds_parse(struct dsa_switch_tree *dst, struct dsa_switch *ds)
+{
+	struct device_node *port;
+	u32 index;
+	int err;
+
+	for (index = 0; index < DSA_MAX_PORTS; index++) {
+		port = ds->ports[index].dn;
+		if (!port)
+			continue;
+
+		if (dsa_port_is_cpu(port)) {
+			err = dsa_cpu_parse(port, index, dst, ds);
+			if (err)
+				return err;
+		}
+	}
+
+	pr_info("DSA: switch %d %d parsed\n", dst->tree, ds->index);
+
+	return 0;
+}
+
+static int dsa_dst_parse(struct dsa_switch_tree *dst)
+{
+	struct dsa_switch *ds;
+	u32 index;
+	int err;
+
+	for (index = 0; index < DSA_MAX_SWITCHES; index++) {
+		ds = dst->ds[index];
+		if (!ds)
+			continue;
+
+		err = dsa_ds_parse(dst, ds);
+		if (err)
+			return err;
+	}
+
+	if (!dst->master_netdev) {
+		pr_warn("Tree has no master device\n");
+		return -EINVAL;
+	}
+
+	pr_info("DSA: tree %d parsed\n", dst->tree);
+
+	return 0;
+}
+
+static int dsa_parse_ports_dn(struct device_node *ports, struct dsa_switch *ds)
+{
+	struct device_node *port;
+	int err;
+	u32 reg;
+
+	for_each_available_child_of_node(ports, port) {
+		err = of_property_read_u32(port, "reg", &reg);
+		if (err)
+			return err;
+
+		if (reg >= DSA_MAX_PORTS)
+			return -EINVAL;
+
+		ds->ports[reg].dn = port;
+	}
+
+	return 0;
+}
+
+static int dsa_parse_member(struct device_node *np, u32 *tree, u32 *index)
+{
+	int err;
+
+	*tree = *index = 0;
+
+	err = of_property_read_u32_index(np, "dsa,member", 0, tree);
+	if (err) {
+		/* Does not exist, but it is optional */
+		if (err == -EINVAL)
+			return 0;
+		return err;
+	}
+
+	err = of_property_read_u32_index(np, "dsa,member", 1, index);
+	if (err)
+		return err;
+
+	if (*index >= DSA_MAX_SWITCHES)
+		return -EINVAL;
+
+	return 0;
+}
+
+static struct device_node *dsa_get_ports(struct dsa_switch *ds,
+					 struct device_node *np)
+{
+	struct device_node *ports;
+
+	ports = of_get_child_by_name(np, "ports");
+	if (!ports) {
+		dev_err(ds->dev, "no ports child node found\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	return ports;
+}
+
+static int _dsa_register_switch(struct dsa_switch *ds, struct device_node *np)
+{
+	struct device_node *ports = dsa_get_ports(ds, np);
+	struct dsa_switch_tree *dst;
+	u32 tree, index;
+	int err;
+
+	err = dsa_parse_member(np, &tree, &index);
+	if (err)
+		return err;
+
+	if (IS_ERR(ports))
+		return PTR_ERR(ports);
+
+	err = dsa_parse_ports_dn(ports, ds);
+	if (err)
+		return err;
+
+	dst = dsa_get_dst(tree);
+	if (!dst) {
+		dst = dsa_add_dst(tree);
+		if (!dst)
+			return -ENOMEM;
+	}
+
+	if (dst->ds[index]) {
+		err = -EBUSY;
+		goto out;
+	}
+
+	ds->dst = dst;
+	ds->index = index;
+	dsa_dst_add_ds(dst, ds, index);
+
+	err = dsa_dst_complete(dst);
+	if (err < 0)
+		goto out_del_dst;
+
+	if (err == 1) {
+		/* Not all switches registered yet */
+		err = 0;
+		goto out;
+	}
+
+	if (dst->applied) {
+		pr_info("DSA: Disjoint trees?\n");
+		return -EINVAL;
+	}
+
+	err = dsa_dst_parse(dst);
+	if (err)
+		goto out_del_dst;
+
+	err = dsa_dst_apply(dst);
+	if (err) {
+		dsa_dst_unapply(dst);
+		goto out_del_dst;
+	}
+
+	dsa_put_dst(dst);
+	return 0;
+
+out_del_dst:
+	dsa_dst_del_ds(dst, ds, ds->index);
+out:
+	dsa_put_dst(dst);
+
+	return err;
+}
+
+int dsa_register_switch(struct dsa_switch *ds, struct device_node *np)
+{
+	int err;
+
+	mutex_lock(&dsa2_mutex);
+	err = _dsa_register_switch(ds, np);
+	mutex_unlock(&dsa2_mutex);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(dsa_register_switch);
+
+void _dsa_unregister_switch(struct dsa_switch *ds)
+{
+	struct dsa_switch_tree *dst = ds->dst;
+
+	dsa_dst_unapply(dst);
+
+	dsa_dst_del_ds(dst, ds, ds->index);
+}
+
+void dsa_unregister_switch(struct dsa_switch *ds)
+{
+	mutex_lock(&dsa2_mutex);
+	_dsa_unregister_switch(ds);
+	mutex_unlock(&dsa2_mutex);
+}
+EXPORT_SYMBOL_GPL(dsa_unregister_switch);
+
diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index 72f7b8989cfb..b42f1a5f95f3 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -59,7 +59,7 @@ const struct dsa_device_ops *dsa_resolve_tag_protocol(int tag_protocol);
 extern const struct dsa_device_ops notag_netdev_ops;
 void dsa_slave_mii_bus_init(struct dsa_switch *ds);
 int dsa_slave_create(struct dsa_switch *ds, struct device *parent,
-		     int port, char *name);
+		     int port, const char *name);
 void dsa_slave_destroy(struct net_device *slave_dev);
 int dsa_slave_suspend(struct net_device *slave_dev);
 int dsa_slave_resume(struct net_device *slave_dev);
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 35e5f0f6688b..15a492261895 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -1099,14 +1099,18 @@ int dsa_slave_resume(struct net_device *slave_dev)
 }
 
 int dsa_slave_create(struct dsa_switch *ds, struct device *parent,
-		     int port, char *name)
+		     int port, const char *name)
 {
-	struct net_device *master = ds->dst->master_netdev;
 	struct dsa_switch_tree *dst = ds->dst;
+	struct net_device *master;
 	struct net_device *slave_dev;
 	struct dsa_slave_priv *p;
 	int ret;
 
+	master = ds->dst->master_netdev;
+	if (ds->master_netdev)
+		master = ds->master_netdev;
+
 	slave_dev = alloc_netdev(sizeof(struct dsa_slave_priv), name,
 				 NET_NAME_UNKNOWN, ether_setup);
 	if (slave_dev == NULL)
-- 
2.8.1

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