Re: [PATCH v2 3/3] powerpc/numa: Support coregroup on PowerNV

Coregroup support on powerpc has so far been limited to PowerVM LPARs.
However, PowerNV can also support coregroups when firmware exposes the
required coregroup information through the associativity hierarchy.

Detect coregroup support by checking whether primary_domain_index is the
penultimate domain in the CPU node's ibm,associativity property. On
PowerNV, a non-penultimate primary_domain_index indicates that firmware
provides an additional level for coregroup information.

This keeps the logic compatible with PowerVM systems, where
primary_domain_index is likewise not the penultimate associativity
domain.

Signed-off-by: Srikar Dronamraju <redacted>
---
Changelog from v1: https://lkml.kernel.org/r/20260524010017.140408-1-srikar@linux.ibm.com
- Handle comments from Christophe Leroy; make code more flat

 arch/powerpc/mm/numa.c | 56 ++++++++++++++++++++++++++++++++++--------
 1 file changed, 46 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 9aa71eb7e96b..e97b624203ea 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c

@@ -889,12 +889,32 @@ static int __init numa_setup_drmem_lmb(struct drmem_lmb *lmb,
 	return 0;
 }
 
+/*
+ * If hierarchy extends beyond primary_domain_index + 1, then next
+ * level corresponds to coregroup.
+ */
+static int detect_and_enable_coregroup(const __be32 *associativity, int index)

+
 static int __init parse_numa_properties(void)
 {
 	struct device_node *memory, *pci;
-	int default_nid = 0;
-	unsigned long i;
+	int default_nid = 0, index = 0;
 	const __be32 *associativity;
+	unsigned long i;
 
 	if (numa_enabled == 0) {
 		pr_warn("disabled by user\n");

@@ -927,7 +947,6 @@ static int __init parse_numa_properties(void)
 	 */
 	for_each_present_cpu(i) {
 		__be32 vphn_assoc[VPHN_ASSOC_BUFSIZE];
-		struct device_node *cpu;
 		int nid = NUMA_NO_NODE;
 
 		memset(vphn_assoc, 0, VPHN_ASSOC_BUFSIZE * sizeof(__be32));

@@ -935,7 +954,9 @@ static int __init parse_numa_properties(void)
 		if (__vphn_get_associativity(i, vphn_assoc) == 0) {
 			nid = associativity_to_nid(vphn_assoc);
 			initialize_form1_numa_distance(vphn_assoc);
+			index = detect_and_enable_coregroup(vphn_assoc, index);
 		} else {
+			struct device_node *cpu;
 
 			/*
 			 * Don't fall back to default_nid yet -- we will plug

@@ -948,6 +969,7 @@ static int __init parse_numa_properties(void)
 			associativity = of_get_associativity(cpu);
 			if (associativity) {
 				nid = associativity_to_nid(associativity);
+				index = detect_and_enable_coregroup(associativity, index);
 				initialize_form1_numa_distance(associativity);
 			}
 			of_node_put(cpu);

@@ -1445,7 +1467,9 @@ static long vphn_get_associativity(unsigned long cpu,
 
 int cpu_to_coregroup_id(int cpu)
 {
-	__be32 associativity[VPHN_ASSOC_BUFSIZE] = {0};
+	int coregroup_id = cpu_to_core_id(cpu);
+	struct device_node *cpunode = NULL;
+	const __be32 *associativity;
 	int index;
 
 	if (cpu < 0 || cpu > nr_cpu_ids)

@@ -1454,19 +1478,31 @@ int cpu_to_coregroup_id(int cpu)
 	if (!coregroup_enabled)
 		goto out;
 
-	if (!firmware_has_feature(FW_FEATURE_VPHN))
-		goto out;
+	if (firmware_has_feature(FW_FEATURE_VPHN)) {
+		__be32 tmp[VPHN_ASSOC_BUFSIZE] = {0};
 
-	if (vphn_get_associativity(cpu, associativity))
+		if (vphn_get_associativity(cpu, tmp))
+			goto out;
+
+		associativity = tmp;
+
+	} else {
+		cpunode = of_get_cpu_node(cpu, NULL);
+		if (!cpunode)
+			goto out;
+
+		associativity = of_get_associativity(cpunode);
+	}
+	if (!associativity)
 		goto out;
 
 	index = of_read_number(associativity, 1);
 	if (index > primary_domain_index + 1)
-		return of_read_number(&associativity[index - 1], 1);
+		coregroup_id = of_read_number(&associativity[index - 1], 1);
 
 out:
-	return cpu_to_core_id(cpu);
-}