interconnect: Add interconnect_graph file to debugfs

The interconnect graphs can be difficult to understand and the current
"interconnect_summary" file doesn't even display links in any way.

Add a new "interconnect_graph" file to debugfs in the graphviz "dot"
format which describes interconnect providers, nodes and links.

The file is human-readable and can be visualized by piping through
graphviz. Example:

ssh $TARGET cat /sys/kernel/debug/interconnect/interconnect_graph \
	| dot -Tsvg > interconnect_graph.svg
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>

Documentation/driver-api/interconnect.rst

@@ -91,3 +91,25 @@ Interconnect consumers are the clients which use the interconnect APIs to
 get paths between endpoints and set their bandwidth/latency/QoS requirements
 for these interconnect paths.  These interfaces are not currently
 documented.
+
+Interconnect debugfs interfaces
+-------------------------------
+
+Like several other subsystems interconnect will create some files for debugging
+and introspection. Files in debugfs are not considered ABI so application
+software shouldn't rely on format details change between kernel versions.
+
+``/sys/kernel/debug/interconnect/interconnect_summary``:
+
+Show all interconnect nodes in the system with their aggregated bandwidth
+request. Indented under each node show bandwidth requests from each device.
+
+``/sys/kernel/debug/interconnect/interconnect_graph``:
+
+Show the interconnect graph in the graphviz dot format. It shows all
+interconnect nodes and links in the system and groups together nodes from the
+same provider as subgraphs. The format is human-readable and can also be piped
+through dot to generate diagrams in many graphical formats::
+
+        $ cat /sys/kernel/debug/interconnect/interconnect_graph | \
+                dot -Tsvg > interconnect_graph.svg

drivers/interconnect/core.c

@@ -71,6 +71,70 @@ static int icc_summary_show(struct seq_file *s, void *data)
 }
 DEFINE_SHOW_ATTRIBUTE(icc_summary);
 
+static void icc_graph_show_link(struct seq_file *s, int level,
+				struct icc_node *n, struct icc_node *m)
+{
+	seq_printf(s, "%s\"%d:%s\" -> \"%d:%s\"\n",
+		   level == 2 ? "\t\t" : "\t",
+		   n->id, n->name, m->id, m->name);
+}
+
+static void icc_graph_show_node(struct seq_file *s, struct icc_node *n)
+{
+	seq_printf(s, "\t\t\"%d:%s\" [label=\"%d:%s",
+		   n->id, n->name, n->id, n->name);
+	seq_printf(s, "\n\t\t\t|avg_bw=%ukBps", n->avg_bw);
+	seq_printf(s, "\n\t\t\t|peak_bw=%ukBps", n->peak_bw);
+	seq_puts(s, "\"]\n");
+}
+
+static int icc_graph_show(struct seq_file *s, void *data)
+{
+	struct icc_provider *provider;
+	struct icc_node *n;
+	int cluster_index = 0;
+	int i;
+
+	seq_puts(s, "digraph {\n\trankdir = LR\n\tnode [shape = record]\n");
+	mutex_lock(&icc_lock);
+
+	/* draw providers as cluster subgraphs */
+	cluster_index = 0;
+	list_for_each_entry(provider, &icc_providers, provider_list) {
+		seq_printf(s, "\tsubgraph cluster_%d {\n", ++cluster_index);
+		if (provider->dev)
+			seq_printf(s, "\t\tlabel = \"%s\"\n",
+				   dev_name(provider->dev));
+
+		/* draw nodes */
+		list_for_each_entry(n, &provider->nodes, node_list)
+			icc_graph_show_node(s, n);
+
+		/* draw internal links */
+		list_for_each_entry(n, &provider->nodes, node_list)
+			for (i = 0; i < n->num_links; ++i)
+				if (n->provider == n->links[i]->provider)
+					icc_graph_show_link(s, 2, n,
+							    n->links[i]);
+
+		seq_puts(s, "\t}\n");
+	}
+
+	/* draw external links */
+	list_for_each_entry(provider, &icc_providers, provider_list)
+		list_for_each_entry(n, &provider->nodes, node_list)
+			for (i = 0; i < n->num_links; ++i)
+				if (n->provider != n->links[i]->provider)
+					icc_graph_show_link(s, 1, n,
+							    n->links[i]);
+
+	mutex_unlock(&icc_lock);
+	seq_puts(s, "}");
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(icc_graph);
+
 static struct icc_node *node_find(const int id)
 {
 	return idr_find(&icc_idr, id);
@@ -827,6 +891,8 @@ static int __init icc_init(void)
 	icc_debugfs_dir = debugfs_create_dir("interconnect", NULL);
 	debugfs_create_file("interconnect_summary", 0444,
 			    icc_debugfs_dir, NULL, &icc_summary_fops);
+	debugfs_create_file("interconnect_graph", 0444,
+			    icc_debugfs_dir, NULL, &icc_graph_fops);
 	return 0;
 }