[PATCH 05/33] ACPI / PPTT: Add a helper to fill a cpumask from a cache_id

Ben Horgan
2025-11-07T12:35:54Z

From: James Morse <james.morse@arm.com>

MPAM identifies CPUs by the cache_id in the PPTT cache structure.

The driver needs to know which CPUs are associated with the cache.
The CPUs may not all be online, so cacheinfo does not have the
information.

Add a helper to pull this information out of the PPTT.

CC: Rohit Mathew <Rohit.Mathew@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
Changes since v3:
Equivalent changes to the previous patch:
Tags dropped due to rework
Fallout/simplification from adding acpi_pptt_cache_v1_full
Look for each cache type before incrementing level
---
drivers/acpi/pptt.c | 62 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/acpi.h | 6 +++++
2 files changed, 68 insertions(+)

diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index 71841c106020..7b4cb17c12c0 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c
@@ -981,3 +981,65 @@ int find_acpi_cache_level_from_id(u32 cache_id)

return -ENOENT;
}
+
+/**
+ * acpi_pptt_get_cpumask_from_cache_id() - Get the cpus associated with the
+ * specified cache
+ * @cache_id: The id field of the cache
+ * @cpus: Where to build the cpumask
+ *
+ * Determine which CPUs are below this cache in the PPTT. This allows the property
+ * to be found even if the CPUs are offline.
+ *
+ * The PPTT table must be rev 3 or later,
+ *
+ * Return: -ENOENT if the PPTT doesn't exist, or the cache cannot be found.
+ * Otherwise returns 0 and sets the cpus in the provided cpumask.
+ */
+int acpi_pptt_get_cpumask_from_cache_id(u32 cache_id, cpumask_t *cpus)
+{
+ int cpu;
+ struct acpi_table_header *table;
+
+ cpumask_clear(cpus);
+
+ table = acpi_get_pptt();
+ if (!table)
+ return -ENOENT;
+
+ if (table->revision < 3)
+ return -ENOENT;
+
+ for_each_possible_cpu(cpu) {
+ bool not_empty = true;
+ u32 acpi_cpu_id;
+ struct acpi_pptt_cache_v1_full *cache;
+ struct acpi_pptt_processor *cpu_node;
+
+ acpi_cpu_id = get_acpi_id_for_cpu(cpu);
+ cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
+ if (!cpu_node)
+ continue;
+
+ for (int level = 1; not_empty; level++) {
+ int cache_type[] = {CACHE_TYPE_INST, CACHE_TYPE_DATA, CACHE_TYPE_UNIFIED};
+
+ not_empty = false;
+ for (int i = 0; i < ARRAY_SIZE(cache_type); i++) {
+ cache = acpi_find_cache_node(table, acpi_cpu_id, cache_type[i],
+ level, &cpu_node);
+
+ if (!cache)
+ continue;
+
+ not_empty = true;
+
+ if (acpi_pptt_cache_id_is_valid(cache) &&
+ cache->extra.cache_id == cache_id)
+ cpumask_set_cpu(cpu, cpus);
+ }
+ }
+ }
+
+ return 0;
+}
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index be074bdfd4d1..a9dbacabdf89 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -1543,6 +1543,7 @@ int find_acpi_cpu_topology_package(unsigned int cpu);
int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus);
int find_acpi_cache_level_from_id(u32 cache_id);
+int acpi_pptt_get_cpumask_from_cache_id(u32 cache_id, cpumask_t *cpus);
#else
static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
{
@@ -1570,6 +1571,11 @@ static inline int find_acpi_cache_level_from_id(u32 cache_id)
{
return -ENOENT;
}
+static inline int acpi_pptt_get_cpumask_from_cache_id(u32 cache_id,
+ cpumask_t *cpus)
+{
+ return -ENOENT;
+}
#endif

void acpi_arch_init(void);
--
2.43.0