net: dsa: Allow default tag protocol to be overridden from DT

Some combinations of tag protocols and Ethernet controllers are
incompatible, and it is hard for the driver to keep track of these.

Therefore, allow the device tree author (typically the board vendor)
to inform the driver of this fact by selecting an alternate protocol
that is known to work.
Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dsa.h

@@ -149,6 +149,11 @@ struct dsa_switch_tree {
 	/* Tagging protocol operations */
 	const struct dsa_device_ops *tag_ops;
 
+	/* Default tagging protocol preferred by the switches in this
+	 * tree.
+	 */
+	enum dsa_tag_protocol default_proto;
+
 	/*
 	 * Configuration data for the platform device that owns
 	 * this dsa switch tree instance.

net/dsa/dsa2.c

@@ -668,6 +668,30 @@ static const struct devlink_ops dsa_devlink_ops = {
 	.sb_occ_tc_port_bind_get	= dsa_devlink_sb_occ_tc_port_bind_get,
 };
 
+static int dsa_switch_setup_tag_protocol(struct dsa_switch *ds)
+{
+	const struct dsa_device_ops *tag_ops = ds->dst->tag_ops;
+	struct dsa_switch_tree *dst = ds->dst;
+	int port, err;
+
+	if (tag_ops->proto == dst->default_proto)
+		return 0;
+
+	for (port = 0; port < ds->num_ports; port++) {
+		if (!dsa_is_cpu_port(ds, port))
+			continue;
+
+		err = ds->ops->change_tag_protocol(ds, port, tag_ops->proto);
+		if (err) {
+			dev_err(ds->dev, "Unable to use tag protocol \"%s\": %pe\n",
+				tag_ops->name, ERR_PTR(err));
+			return err;
+		}
+	}
+
+	return 0;
+}
+
 static int dsa_switch_setup(struct dsa_switch *ds)
 {
 	struct dsa_devlink_priv *dl_priv;
@@ -718,6 +742,10 @@ static int dsa_switch_setup(struct dsa_switch *ds)
 	if (err < 0)
 		goto unregister_notifier;
 
+	err = dsa_switch_setup_tag_protocol(ds);
+	if (err)
+		goto teardown;
+
 	devlink_params_publish(ds->devlink);
 
 	if (!ds->slave_mii_bus && ds->ops->phy_read) {
@@ -1068,34 +1096,60 @@ static enum dsa_tag_protocol dsa_get_tag_protocol(struct dsa_port *dp,
 	return ds->ops->get_tag_protocol(ds, dp->index, tag_protocol);
 }
 
-static int dsa_port_parse_cpu(struct dsa_port *dp, struct net_device *master)
+static int dsa_port_parse_cpu(struct dsa_port *dp, struct net_device *master,
+			      const char *user_protocol)
 {
 	struct dsa_switch *ds = dp->ds;
 	struct dsa_switch_tree *dst = ds->dst;
 	const struct dsa_device_ops *tag_ops;
-	enum dsa_tag_protocol tag_protocol;
+	enum dsa_tag_protocol default_proto;
 
-	tag_protocol = dsa_get_tag_protocol(dp, master);
-	if (dst->tag_ops) {
-		if (dst->tag_ops->proto != tag_protocol) {
+	/* Find out which protocol the switch would prefer. */
+	default_proto = dsa_get_tag_protocol(dp, master);
+	if (dst->default_proto) {
+		if (dst->default_proto != default_proto) {
 			dev_err(ds->dev,
 				"A DSA switch tree can have only one tagging protocol\n");
 			return -EINVAL;
 		}
-		/* In the case of multiple CPU ports per switch, the tagging
-		 * protocol is still reference-counted only per switch tree, so
-		 * nothing to do here.
-		 */
 	} else {
-		tag_ops = dsa_tag_driver_get(tag_protocol);
+		dst->default_proto = default_proto;
+	}
+
+	/* See if the user wants to override that preference. */
+	if (user_protocol) {
+		if (!ds->ops->change_tag_protocol) {
+			dev_err(ds->dev, "Tag protocol cannot be modified\n");
+			return -EINVAL;
+		}
+
+		tag_ops = dsa_find_tagger_by_name(user_protocol);
+	} else {
+		tag_ops = dsa_tag_driver_get(default_proto);
+	}
+
 	if (IS_ERR(tag_ops)) {
 		if (PTR_ERR(tag_ops) == -ENOPROTOOPT)
 			return -EPROBE_DEFER;
+
 		dev_warn(ds->dev, "No tagger for this switch\n");
-			dp->master = NULL;
 		return PTR_ERR(tag_ops);
 	}
 
+	if (dst->tag_ops) {
+		if (dst->tag_ops != tag_ops) {
+			dev_err(ds->dev,
+				"A DSA switch tree can have only one tagging protocol\n");
+
+			dsa_tag_driver_put(tag_ops);
+			return -EINVAL;
+		}
+
+		/* In the case of multiple CPU ports per switch, the tagging
+		 * protocol is still reference-counted only per switch tree.
+		 */
+		dsa_tag_driver_put(tag_ops);
+	} else {
 		dst->tag_ops = tag_ops;
 	}
 
@@ -1104,6 +1158,19 @@ static int dsa_port_parse_cpu(struct dsa_port *dp, struct net_device *master)
 	dsa_port_set_tag_protocol(dp, dst->tag_ops);
 	dp->dst = dst;
 
+	/* At this point, the tree may be configured to use a different
+	 * tagger than the one chosen by the switch driver during
+	 * .setup, in the case when a user selects a custom protocol
+	 * through the DT.
+	 *
+	 * This is resolved by syncing the driver with the tree in
+	 * dsa_switch_setup_tag_protocol once .setup has run and the
+	 * driver is ready to accept calls to .change_tag_protocol. If
+	 * the driver does not support the custom protocol at that
+	 * point, the tree is wholly rejected, thereby ensuring that the
+	 * tree and driver are always in agreement on the protocol to
+	 * use.
+	 */
 	return 0;
 }
 
@@ -1117,12 +1184,14 @@ static int dsa_port_parse_of(struct dsa_port *dp, struct device_node *dn)
 
 	if (ethernet) {
 		struct net_device *master;
+		const char *user_protocol;
 
 		master = of_find_net_device_by_node(ethernet);
 		if (!master)
 			return -EPROBE_DEFER;
 
-		return dsa_port_parse_cpu(dp, master);
+		user_protocol = of_get_property(dn, "dsa-tag-protocol", NULL);
+		return dsa_port_parse_cpu(dp, master, user_protocol);
 	}
 
 	if (link)
@@ -1234,7 +1303,7 @@ static int dsa_port_parse(struct dsa_port *dp, const char *name,
 
 		dev_put(master);
 
-		return dsa_port_parse_cpu(dp, master);
+		return dsa_port_parse_cpu(dp, master, NULL);
 	}
 
 	if (!strcmp(name, "dsa"))