[v8,net-next,08/11] net: dsa: allow changing the tag protocol via the "tagging" device attribute

diff --git a/Documentation/ABI/testing/sysfs-class-net-dsa b/Documentation/ABI/testing/sysfs-class-net-dsa
index 985d84c585c6..e2da26b44dd0 100644
--- a/Documentation/ABI/testing/sysfs-class-net-dsa
+++ b/Documentation/ABI/testing/sysfs-class-net-dsa
@@ -3,5 +3,12 @@  Date:		August 2018
 KernelVersion:	4.20
 Contact:	netdev@vger.kernel.org
 Description:
-		String indicating the type of tagging protocol used by the
-		DSA slave network device.
+		On read, this file returns a string indicating the type of
+		tagging protocol used by the DSA network devices that are
+		attached to this master interface.
+		On write, this file changes the tagging protocol of the
+		attached DSA switches, if this operation is supported by the
+		driver. Changing the tagging protocol must be done with the DSA
+		interfaces and the master interface all administratively down.
+		See the "name" field of each registered struct dsa_device_ops
+		for a list of valid values.
diff --git a/include/net/dsa.h b/include/net/dsa.h
index b8af1d6c879a..7ea3918b2e61 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -485,9 +485,18 @@  static inline bool dsa_port_is_vlan_filtering(const struct dsa_port *dp)
 typedef int dsa_fdb_dump_cb_t(const unsigned char *addr, u16 vid,
 			      bool is_static, void *data);
 struct dsa_switch_ops {
+	/*
+	 * Tagging protocol helpers called for the CPU ports and DSA links.
+	 * @get_tag_protocol retrieves the initial tagging protocol and is
+	 * mandatory. Switches which can operate using multiple tagging
+	 * protocols should implement @change_tag_protocol and report in
+	 * @get_tag_protocol the tagger in current use.
+	 */
 	enum dsa_tag_protocol (*get_tag_protocol)(struct dsa_switch *ds,
 						  int port,
 						  enum dsa_tag_protocol mprot);
+	int	(*change_tag_protocol)(struct dsa_switch *ds, int port,
+				       enum dsa_tag_protocol proto);
 
 	int	(*setup)(struct dsa_switch *ds);
 	void	(*teardown)(struct dsa_switch *ds);
diff --git a/net/dsa/dsa.c b/net/dsa/dsa.c
index f4ce3c5826a0..84cad1be9ce4 100644
--- a/net/dsa/dsa.c
+++ b/net/dsa/dsa.c
@@ -84,6 +84,32 @@  const char *dsa_tag_protocol_to_str(const struct dsa_device_ops *ops)
 	return ops->name;
 };
 
+/* Function takes a reference on the module owning the tagger,
+ * so dsa_tag_driver_put must be called afterwards.
+ */
+const struct dsa_device_ops *dsa_find_tagger_by_name(const char *buf)
+{
+	const struct dsa_device_ops *ops = ERR_PTR(-ENOPROTOOPT);
+	struct dsa_tag_driver *dsa_tag_driver;
+
+	mutex_lock(&dsa_tag_drivers_lock);
+	list_for_each_entry(dsa_tag_driver, &dsa_tag_drivers_list, list) {
+		const struct dsa_device_ops *tmp = dsa_tag_driver->ops;
+
+		if (!sysfs_streq(buf, tmp->name))
+			continue;
+
+		if (!try_module_get(dsa_tag_driver->owner))
+			break;
+
+		ops = tmp;
+		break;
+	}
+	mutex_unlock(&dsa_tag_drivers_lock);
+
+	return ops;
+}
+
 const struct dsa_device_ops *dsa_tag_driver_get(int tag_protocol)
 {
 	struct dsa_tag_driver *dsa_tag_driver;
diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index 63035a898ca8..96249c4ad5f2 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -942,6 +942,57 @@  static void dsa_tree_teardown(struct dsa_switch_tree *dst)
 	dst->setup = false;
 }
 
+/* Since the dsa/tagging sysfs device attribute is per master, the assumption
+ * is that all DSA switches within a tree share the same tagger, otherwise
+ * they would have formed disjoint trees (different "dsa,member" values).
+ */
+int dsa_tree_change_tag_proto(struct dsa_switch_tree *dst,
+			      struct net_device *master,
+			      const struct dsa_device_ops *tag_ops,
+			      const struct dsa_device_ops *old_tag_ops)
+{
+	struct dsa_notifier_tag_proto_info info;
+	struct dsa_port *dp;
+	int err = -EBUSY;
+
+	if (!rtnl_trylock())
+		return restart_syscall();
+
+	/* At the moment we don't allow changing the tag protocol under
+	 * traffic. The rtnl_mutex also happens to serialize concurrent
+	 * attempts to change the tagging protocol. If we ever lift the IFF_UP
+	 * restriction, there needs to be another mutex which serializes this.
+	 */
+	if (master->flags & IFF_UP)
+		goto out_unlock;
+
+	list_for_each_entry(dp, &dst->ports, list) {
+		if (!dsa_is_user_port(dp->ds, dp->index))
+			continue;
+
+		if (dp->slave->flags & IFF_UP)
+			goto out_unlock;
+	}
+
+	info.tag_ops = tag_ops;
+	err = dsa_tree_notify(dst, DSA_NOTIFIER_TAG_PROTO, &info);
+	if (err)
+		goto out_unwind_tagger;
+
+	dst->tag_ops = tag_ops;
+
+	rtnl_unlock();
+
+	return 0;
+
+out_unwind_tagger:
+	info.tag_ops = old_tag_ops;
+	dsa_tree_notify(dst, DSA_NOTIFIER_TAG_PROTO, &info);
+out_unlock:
+	rtnl_unlock();
+	return err;
+}
+
 static struct dsa_port *dsa_port_touch(struct dsa_switch *ds, int index)
 {
 	struct dsa_switch_tree *dst = ds->dst;
@@ -1038,9 +1089,7 @@  static int dsa_port_parse_cpu(struct dsa_port *dp, struct net_device *master)
 
 	dp->master = master;
 	dp->type = DSA_PORT_TYPE_CPU;
-	dp->filter = dst->tag_ops->filter;
-	dp->rcv = dst->tag_ops->rcv;
-	dp->tag_ops = dst->tag_ops;
+	dsa_port_set_tag_protocol(dp, dst->tag_ops);
 	dp->dst = dst;
 
 	return 0;
diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index 3cc1e6d76e3a..edca57b558ad 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -28,6 +28,7 @@  enum {
 	DSA_NOTIFIER_VLAN_ADD,
 	DSA_NOTIFIER_VLAN_DEL,
 	DSA_NOTIFIER_MTU,
+	DSA_NOTIFIER_TAG_PROTO,
 };
 
 /* DSA_NOTIFIER_AGEING_TIME */
@@ -82,6 +83,11 @@  struct dsa_notifier_mtu_info {
 	int mtu;
 };
 
+/* DSA_NOTIFIER_TAG_PROTO_* */
+struct dsa_notifier_tag_proto_info {
+	const struct dsa_device_ops *tag_ops;
+};
+
 struct dsa_switchdev_event_work {
 	struct dsa_switch *ds;
 	int port;
@@ -115,6 +121,7 @@  struct dsa_slave_priv {
 /* dsa.c */
 const struct dsa_device_ops *dsa_tag_driver_get(int tag_protocol);
 void dsa_tag_driver_put(const struct dsa_device_ops *ops);
+const struct dsa_device_ops *dsa_find_tagger_by_name(const char *buf);
 
 bool dsa_schedule_work(struct work_struct *work);
 const char *dsa_tag_protocol_to_str(const struct dsa_device_ops *ops);
@@ -139,6 +146,8 @@  static inline struct net_device *dsa_master_find_slave(struct net_device *dev,
 }
 
 /* port.c */
+void dsa_port_set_tag_protocol(struct dsa_port *cpu_dp,
+			       const struct dsa_device_ops *tag_ops);
 int dsa_port_set_state(struct dsa_port *dp, u8 state);
 int dsa_port_enable_rt(struct dsa_port *dp, struct phy_device *phy);
 int dsa_port_enable(struct dsa_port *dp, struct phy_device *phy);
@@ -201,6 +210,8 @@  int dsa_slave_suspend(struct net_device *slave_dev);
 int dsa_slave_resume(struct net_device *slave_dev);
 int dsa_slave_register_notifier(void);
 void dsa_slave_unregister_notifier(void);
+void dsa_slave_setup_tagger(struct net_device *slave);
+int dsa_slave_change_mtu(struct net_device *dev, int new_mtu);
 
 static inline struct dsa_port *dsa_slave_to_port(const struct net_device *dev)
 {
@@ -285,6 +296,10 @@  void dsa_lag_map(struct dsa_switch_tree *dst, struct net_device *lag);
 void dsa_lag_unmap(struct dsa_switch_tree *dst, struct net_device *lag);
 int dsa_tree_notify(struct dsa_switch_tree *dst, unsigned long e, void *v);
 int dsa_broadcast(unsigned long e, void *v);
+int dsa_tree_change_tag_proto(struct dsa_switch_tree *dst,
+			      struct net_device *master,
+			      const struct dsa_device_ops *tag_ops,
+			      const struct dsa_device_ops *old_tag_ops);
 
 extern struct list_head dsa_tree_list;
 
diff --git a/net/dsa/master.c b/net/dsa/master.c
index cb3a5cf99b25..052a977914a6 100644
--- a/net/dsa/master.c
+++ b/net/dsa/master.c
@@ -280,7 +280,44 @@  static ssize_t tagging_show(struct device *d, struct device_attribute *attr,
 	return sprintf(buf, "%s\n",
 		       dsa_tag_protocol_to_str(cpu_dp->tag_ops));
 }
-static DEVICE_ATTR_RO(tagging);
+
+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,
diff --git a/net/dsa/port.c b/net/dsa/port.c
index a8886cf40160..5e079a61528e 100644
--- a/net/dsa/port.c
+++ b/net/dsa/port.c
@@ -526,6 +526,14 @@  int dsa_port_vlan_del(struct dsa_port *dp,
 	return dsa_port_notify(dp, DSA_NOTIFIER_VLAN_DEL, &info);
 }
 
+void dsa_port_set_tag_protocol(struct dsa_port *cpu_dp,
+			       const struct dsa_device_ops *tag_ops)
+{
+	cpu_dp->filter = tag_ops->filter;
+	cpu_dp->rcv = tag_ops->rcv;
+	cpu_dp->tag_ops = tag_ops;
+}
+
 static struct phy_device *dsa_port_get_phy_device(struct dsa_port *dp)
 {
 	struct device_node *phy_dn;
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index f2fb433f3828..b0571ab4e5a7 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -1430,7 +1430,7 @@  static void dsa_bridge_mtu_normalization(struct dsa_port *dp)
 	dsa_hw_port_list_free(&hw_port_list);
 }
 
-static int dsa_slave_change_mtu(struct net_device *dev, int new_mtu)
+int dsa_slave_change_mtu(struct net_device *dev, int new_mtu)
 {
 	struct net_device *master = dsa_slave_to_master(dev);
 	struct dsa_port *dp = dsa_slave_to_port(dev);
@@ -1708,6 +1708,27 @@  static int dsa_slave_phy_setup(struct net_device *slave_dev)
 	return ret;
 }
 
+void dsa_slave_setup_tagger(struct net_device *slave)
+{
+	struct dsa_port *dp = dsa_slave_to_port(slave);
+	struct dsa_slave_priv *p = netdev_priv(slave);
+	const struct dsa_port *cpu_dp = dp->cpu_dp;
+	struct net_device *master = cpu_dp->master;
+
+	if (cpu_dp->tag_ops->tail_tag)
+		slave->needed_tailroom = cpu_dp->tag_ops->overhead;
+	else
+		slave->needed_headroom = cpu_dp->tag_ops->overhead;
+	/* Try to save one extra realloc later in the TX path (in the master)
+	 * by also inheriting the master's needed headroom and tailroom.
+	 * The 8021q driver also does this.
+	 */
+	slave->needed_headroom += master->needed_headroom;
+	slave->needed_tailroom += master->needed_tailroom;
+
+	p->xmit = cpu_dp->tag_ops->xmit;
+}
+
 static struct lock_class_key dsa_slave_netdev_xmit_lock_key;
 static void dsa_slave_set_lockdep_class_one(struct net_device *dev,
 					    struct netdev_queue *txq,
@@ -1782,16 +1803,6 @@  int dsa_slave_create(struct dsa_port *port)
 	slave_dev->netdev_ops = &dsa_slave_netdev_ops;
 	if (ds->ops->port_max_mtu)
 		slave_dev->max_mtu = ds->ops->port_max_mtu(ds, port->index);
-	if (cpu_dp->tag_ops->tail_tag)
-		slave_dev->needed_tailroom = cpu_dp->tag_ops->overhead;
-	else
-		slave_dev->needed_headroom = cpu_dp->tag_ops->overhead;
-	/* Try to save one extra realloc later in the TX path (in the master)
-	 * by also inheriting the master's needed headroom and tailroom.
-	 * The 8021q driver also does this.
-	 */
-	slave_dev->needed_headroom += master->needed_headroom;
-	slave_dev->needed_tailroom += master->needed_tailroom;
 	SET_NETDEV_DEVTYPE(slave_dev, &dsa_type);
 
 	netdev_for_each_tx_queue(slave_dev, dsa_slave_set_lockdep_class_one,
@@ -1814,8 +1825,8 @@  int dsa_slave_create(struct dsa_port *port)
 
 	p->dp = port;
 	INIT_LIST_HEAD(&p->mall_tc_list);
-	p->xmit = cpu_dp->tag_ops->xmit;
 	port->slave = slave_dev;
+	dsa_slave_setup_tagger(slave_dev);
 
 	rtnl_lock();
 	ret = dsa_slave_change_mtu(slave_dev, ETH_DATA_LEN);
diff --git a/net/dsa/switch.c b/net/dsa/switch.c
index cc0b25f3adea..5026e4143663 100644
--- a/net/dsa/switch.c
+++ b/net/dsa/switch.c
@@ -297,6 +297,58 @@  static int dsa_switch_vlan_del(struct dsa_switch *ds,
 	return 0;
 }
 
+static bool dsa_switch_tag_proto_match(struct dsa_switch *ds, int port,
+				       struct dsa_notifier_tag_proto_info *info)
+{
+	if (dsa_is_cpu_port(ds, port) || dsa_is_dsa_port(ds, port))
+		return true;
+
+	return false;
+}
+
+static int dsa_switch_change_tag_proto(struct dsa_switch *ds,
+				       struct dsa_notifier_tag_proto_info *info)
+{
+	const struct dsa_device_ops *tag_ops = info->tag_ops;
+	int port, err;
+
+	if (!ds->ops->change_tag_protocol)
+		return -EOPNOTSUPP;
+
+	ASSERT_RTNL();
+
+	for (port = 0; port < ds->num_ports; port++) {
+		if (dsa_switch_tag_proto_match(ds, port, info)) {
+			err = ds->ops->change_tag_protocol(ds, port,
+							   tag_ops->proto);
+			if (err)
+				return err;
+
+			if (dsa_is_cpu_port(ds, port))
+				dsa_port_set_tag_protocol(dsa_to_port(ds, port),
+							  tag_ops);
+		}
+	}
+
+	/* Now that changing the tag protocol can no longer fail, let's update
+	 * the remaining bits which are "duplicated for faster access", and the
+	 * bits that depend on the tagger, such as the MTU.
+	 */
+	for (port = 0; port < ds->num_ports; port++) {
+		if (dsa_is_user_port(ds, port)) {
+			struct net_device *slave;
+
+			slave = dsa_to_port(ds, port)->slave;
+			dsa_slave_setup_tagger(slave);
+
+			/* rtnl_mutex is held in dsa_tree_change_tag_proto */
+			dsa_slave_change_mtu(slave, slave->mtu);
+		}
+	}
+
+	return 0;
+}
+
 static int dsa_switch_event(struct notifier_block *nb,
 			    unsigned long event, void *info)
 {
@@ -343,6 +395,9 @@  static int dsa_switch_event(struct notifier_block *nb,
 	case DSA_NOTIFIER_MTU:
 		err = dsa_switch_mtu(ds, info);
 		break;
+	case DSA_NOTIFIER_TAG_PROTO:
+		err = dsa_switch_change_tag_proto(ds, info);
+		break;
 	default:
 		err = -EOPNOTSUPP;
 		break;