[PATCH RFC 2/3] arch_topology: Parse die nodes in /cpu-map

[Troy Mitchell <troy.mitchell@linux.dev>]

The devicetree CPU map can distinguish packages and clusters but cannot
describe multiple dies in one package. Such systems have to flatten all
clusters into the package, making cluster identifiers package-wide and
hiding the die boundary.

Recognize an optional sequence of dieN nodes between a socket and its
clusters, and propagate the die identifier to every CPU below it. Enumerate
clusters independently below each die.

When a CPU map has no dieN nodes, continue parsing its existing package
and cluster hierarchy but pass -1 as the die identifier. Legacy maps
therefore remain compatible without being reported as an explicitly
described die 0.

Signed-off-by: Troy Mitchell <troy.mitchell@linux.dev>
---
 drivers/base/arch_topology.c | 48 +++++++++++++++++++++++++++++++++++---------
 1 file changed, 38 insertions(+), 10 deletions(-)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index ee82827be3351..67a984f3ba8d9 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -498,7 +498,7 @@ static int __init get_cpu_for_node(struct device_node *node)
 }
 
 static int __init parse_core(struct device_node *core, int package_id,
-			     int cluster_id, int core_id)
+			     int die_id, int cluster_id, int core_id)
 {
 	char name[20];
 	bool leaf = true;
@@ -517,6 +517,7 @@ static int __init parse_core(struct device_node *core, int package_id,
 		cpu = get_cpu_for_node(t);
 		if (cpu >= 0) {
 			cpu_topology[cpu].package_id = package_id;
+			cpu_topology[cpu].die_id = die_id;
 			cpu_topology[cpu].cluster_id = cluster_id;
 			cpu_topology[cpu].core_id = core_id;
 			cpu_topology[cpu].thread_id = i;
@@ -538,6 +539,7 @@ static int __init parse_core(struct device_node *core, int package_id,
 		}
 
 		cpu_topology[cpu].package_id = package_id;
+		cpu_topology[cpu].die_id = die_id;
 		cpu_topology[cpu].cluster_id = cluster_id;
 		cpu_topology[cpu].core_id = core_id;
 	} else if (leaf && cpu != -ENODEV) {
@@ -549,7 +551,7 @@ static int __init parse_core(struct device_node *core, int package_id,
 }
 
 static int __init parse_cluster(struct device_node *cluster, int package_id,
-				int cluster_id, int depth)
+				int die_id, int cluster_id, int depth)
 {
 	char name[20];
 	bool leaf = true;
@@ -572,7 +574,7 @@ static int __init parse_cluster(struct device_node *cluster, int package_id,
 			break;
 
 		leaf = false;
-		ret = parse_cluster(c, package_id, i, depth + 1);
+		ret = parse_cluster(c, package_id, die_id, i, depth + 1);
 		if (depth > 0)
 			pr_warn("Topology for clusters of clusters not yet supported\n");
 		if (ret != 0)
@@ -598,7 +600,8 @@ static int __init parse_cluster(struct device_node *cluster, int package_id,
 		}
 
 		if (leaf) {
-			ret = parse_core(c, package_id, cluster_id, core_id++);
+			ret = parse_core(c, package_id, die_id, cluster_id,
+					 core_id++);
 			if (ret != 0)
 				return ret;
 		} else {
@@ -616,6 +619,34 @@ static int __init parse_cluster(struct device_node *cluster, int package_id,
 	return 0;
 }
 
+static int __init parse_die(struct device_node *parent, int package_id)
+{
+	char name[20];
+	bool has_die = false;
+	int die_id = 0, ret;
+
+	do {
+		snprintf(name, sizeof(name), "die%d", die_id);
+		struct device_node *d __free(device_node) =
+			of_get_child_by_name(parent, name);
+
+		if (!d)
+			break;
+
+		has_die = true;
+		ret = parse_cluster(d, package_id, die_id, -1, 0);
+		if (ret)
+			return ret;
+
+		die_id++;
+	} while (1);
+
+	if (!has_die)
+		ret = parse_cluster(parent, package_id, -1, -1, 0);
+
+	return ret;
+}
+
 static int __init parse_socket(struct device_node *socket)
 {
 	char name[20];
@@ -631,7 +662,7 @@ static int __init parse_socket(struct device_node *socket)
 			break;
 
 		has_socket = true;
-		ret = parse_cluster(c, package_id, -1, 0);
+		ret = parse_die(c, package_id);
 		if (ret != 0)
 			return ret;
 
@@ -639,7 +670,7 @@ static int __init parse_socket(struct device_node *socket)
 	} while (1);
 
 	if (!has_socket)
-		ret = parse_cluster(socket, 0, -1, 0);
+		ret = parse_die(socket, 0);
 
 	/*
 	 * Reset the max_smt_thread_num to 1 on failure. Since on failure
@@ -667,10 +698,7 @@ static int __init parse_dt_topology(void)
 		return 0;
 	}
 
-	/*
-	 * When topology is provided cpu-map is essentially a root
-	 * cluster with restricted subnodes.
-	 */
+	/* cpu-map is the root of the processor topology hierarchy. */
 	struct device_node *map __free(device_node) =
 		of_get_child_by_name(cn, "cpu-map");
 

-- 
2.55.0