net: dsa: Expose tagging protocol to user-space

There is no way for user-space to know what a given DSA network device's
tagging protocol is. Expose this information through a dsa/tagging
attribute which reflects the tagging protocol currently in use.

This is helpful for configuration (e.g: none behaves dramatically
different wrt. bridges) as well as for packet capture tools when there
is not a proper Ethernet type available.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/ABI/testing/sysfs-class-net-dsa

@@ -0,0 +1,7 @@
+What:		/sys/class/net/<iface>/tagging
+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.

net/dsa/dsa.c

@@ -70,6 +70,49 @@ const struct dsa_device_ops *dsa_device_ops[DSA_TAG_LAST] = {
 	[DSA_TAG_PROTO_NONE] = &none_ops,
 };
 
+const char *dsa_tag_protocol_to_str(const struct dsa_device_ops *ops)
+{
+	const char *protocol_name[DSA_TAG_LAST] = {
+#ifdef CONFIG_NET_DSA_TAG_BRCM
+		[DSA_TAG_PROTO_BRCM] = "brcm",
+#endif
+#ifdef CONFIG_NET_DSA_TAG_BRCM_PREPEND
+		[DSA_TAG_PROTO_BRCM_PREPEND] = "brcm-prepend",
+#endif
+#ifdef CONFIG_NET_DSA_TAG_DSA
+		[DSA_TAG_PROTO_DSA] = "dsa",
+#endif
+#ifdef CONFIG_NET_DSA_TAG_EDSA
+		[DSA_TAG_PROTO_EDSA] = "edsa",
+#endif
+#ifdef CONFIG_NET_DSA_TAG_KSZ
+		[DSA_TAG_PROTO_KSZ] = "ksz",
+#endif
+#ifdef CONFIG_NET_DSA_TAG_LAN9303
+		[DSA_TAG_PROTO_LAN9303] = "lan9303",
+#endif
+#ifdef CONFIG_NET_DSA_TAG_MTK
+		[DSA_TAG_PROTO_MTK] = "mtk",
+#endif
+#ifdef CONFIG_NET_DSA_TAG_QCA
+		[DSA_TAG_PROTO_QCA] = "qca",
+#endif
+#ifdef CONFIG_NET_DSA_TAG_TRAILER
+		[DSA_TAG_PROTO_TRAILER] = "trailer",
+#endif
+		[DSA_TAG_PROTO_NONE] = "none",
+	};
+	unsigned int i;
+
+	BUILD_BUG_ON(ARRAY_SIZE(protocol_name) != DSA_TAG_LAST);
+
+	for (i = 0; i < ARRAY_SIZE(dsa_device_ops); i++)
+		if (ops == dsa_device_ops[i])
+			return protocol_name[i];
+
+	return protocol_name[DSA_TAG_PROTO_NONE];
+};
+
 const struct dsa_device_ops *dsa_resolve_tag_protocol(int tag_protocol)
 {
 	const struct dsa_device_ops *ops;

net/dsa/dsa_priv.h

@@ -86,6 +86,7 @@ struct dsa_slave_priv {
 /* dsa.c */
 const struct dsa_device_ops *dsa_resolve_tag_protocol(int tag_protocol);
 bool dsa_schedule_work(struct work_struct *work);
+const char *dsa_tag_protocol_to_str(const struct dsa_device_ops *ops);
 
 /* legacy.c */
 #if IS_ENABLED(CONFIG_NET_DSA_LEGACY)

net/dsa/slave.c

@@ -1058,6 +1058,27 @@ static struct device_type dsa_type = {
 	.name	= "dsa",
 };
 
+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 *dp = dsa_slave_to_port(dev);
+
+	return sprintf(buf, "%s\n",
+		       dsa_tag_protocol_to_str(dp->cpu_dp->tag_ops));
+}
+static DEVICE_ATTR_RO(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_slave_phylink_validate(struct net_device *dev,
 				       unsigned long *supported,
 				       struct phylink_link_state *state)
@@ -1353,8 +1374,14 @@ int dsa_slave_create(struct dsa_port *port)
 		goto out_phy;
 	}
 
+	ret = sysfs_create_group(&slave_dev->dev.kobj, &dsa_group);
+	if (ret)
+		goto out_unreg;
+
 	return 0;
 
+out_unreg:
+	unregister_netdev(slave_dev);
 out_phy:
 	rtnl_lock();
 	phylink_disconnect_phy(p->dp->pl);
@@ -1378,6 +1405,7 @@ void dsa_slave_destroy(struct net_device *slave_dev)
 	rtnl_unlock();
 
 	dsa_slave_notify(slave_dev, DSA_PORT_UNREGISTER);
+	sysfs_remove_group(&slave_dev->dev.kobj, &dsa_group);
 	unregister_netdev(slave_dev);
 	phylink_destroy(dp->pl);
 	free_percpu(p->stats64);