net: dsa: document the existing switch tree notifiers and add a new one

The existence of dsa_broadcast has generated some confusion in the past:
https://www.mail-archive.com/netdev@vger.kernel.org/msg365042.html

So let's document the existing dsa_port_notify and dsa_broadcast
functions and explain when each of them should be used.

Also, in fact, the in-between function has always been there but was
lacking a name, and is the main reason for this patch: dsa_tree_notify.
Refactor dsa_broadcast to use it.

This patch also moves dsa_broadcast (a top-level function) to dsa2.c,
where it really belonged in the first place, but had no companion so it
stood with dsa_port_notify.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/dsa/dsa2.c

@@ -21,6 +21,49 @@
 static DEFINE_MUTEX(dsa2_mutex);
 LIST_HEAD(dsa_tree_list);
 
+/**
+ * dsa_tree_notify - Execute code for all switches in a DSA switch tree.
+ * @dst: collection of struct dsa_switch devices to notify.
+ * @e: event, must be of type DSA_NOTIFIER_*
+ * @v: event-specific value.
+ *
+ * Given a struct dsa_switch_tree, this can be used to run a function once for
+ * each member DSA switch. The other alternative of traversing the tree is only
+ * through its ports list, which does not uniquely list the switches.
+ */
+int dsa_tree_notify(struct dsa_switch_tree *dst, unsigned long e, void *v)
+{
+	struct raw_notifier_head *nh = &dst->nh;
+	int err;
+
+	err = raw_notifier_call_chain(nh, e, v);
+
+	return notifier_to_errno(err);
+}
+
+/**
+ * dsa_broadcast - Notify all DSA trees in the system.
+ * @e: event, must be of type DSA_NOTIFIER_*
+ * @v: event-specific value.
+ *
+ * Can be used to notify the switching fabric of events such as cross-chip
+ * bridging between disjoint trees (such as islands of tagger-compatible
+ * switches bridged by an incompatible middle switch).
+ */
+int dsa_broadcast(unsigned long e, void *v)
+{
+	struct dsa_switch_tree *dst;
+	int err = 0;
+
+	list_for_each_entry(dst, &dsa_tree_list, list) {
+		err = dsa_tree_notify(dst, e, v);
+		if (err)
+			break;
+	}
+
+	return err;
+}
+
 /**
  * dsa_lag_map() - Map LAG netdev to a linear LAG ID
  * @dst: Tree in which to record the mapping.

net/dsa/dsa_priv.h

@@ -283,6 +283,8 @@ void dsa_switch_unregister_notifier(struct dsa_switch *ds);
 /* dsa2.c */
 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);
 
 extern struct list_head dsa_tree_list;
 

net/dsa/port.c

@@ -13,31 +13,21 @@
 
 #include "dsa_priv.h"
 
-static int dsa_broadcast(unsigned long e, void *v)
-{
-	struct dsa_switch_tree *dst;
-	int err = 0;
-
-	list_for_each_entry(dst, &dsa_tree_list, list) {
-		struct raw_notifier_head *nh = &dst->nh;
-
-		err = raw_notifier_call_chain(nh, e, v);
-		err = notifier_to_errno(err);
-		if (err)
-			break;
-	}
-
-	return err;
-}
-
+/**
+ * dsa_port_notify - Notify the switching fabric of changes to a port
+ * @dp: port on which change occurred
+ * @e: event, must be of type DSA_NOTIFIER_*
+ * @v: event-specific value.
+ *
+ * Notify all switches in the DSA tree that this port's switch belongs to,
+ * including this switch itself, of an event. Allows the other switches to
+ * reconfigure themselves for cross-chip operations. Can also be used to
+ * reconfigure ports without net_devices (CPU ports, DSA links) whenever
+ * a user port's state changes.
+ */
 static int dsa_port_notify(const struct dsa_port *dp, unsigned long e, void *v)
 {
-	struct raw_notifier_head *nh = &dp->ds->dst->nh;
-	int err;
-
-	err = raw_notifier_call_chain(nh, e, v);
-
-	return notifier_to_errno(err);
+	return dsa_tree_notify(dp->ds->dst, e, v);
 }
 
 int dsa_port_set_state(struct dsa_port *dp, u8 state)