[PATCH v2 04/29] ACPI / PPTT: Add a helper to fill a cpumask from a cache_id

James Morse
2025-09-10T20:43:49Z

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>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
---
Changes since v1:
* Added punctuation to the commit message.
* Removed a comment about an alternative implementaion.
* Made the loop continue with a warning if a CPU is missing from the PPTT.

Changes since RFC:
* acpi_count_levels() now returns a value.
* Converted the table-get stuff to use Jonathan's cleanup helper.
* Dropped Sudeep's Review tag due to the cleanup change.
---
drivers/acpi/pptt.c | 59 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/acpi.h | 6 +++++
2 files changed, 65 insertions(+)

diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index c5f2a51d280b..c379a9952b00 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c
@@ -966,3 +966,62 @@ 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 unified 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)
+{
+ u32 acpi_cpu_id;
+ int level, cpu, num_levels;
+ struct acpi_pptt_cache *cache;
+ struct acpi_pptt_cache_v1 *cache_v1;
+ struct acpi_pptt_processor *cpu_node;
+ struct acpi_table_header *table __free(acpi_table) = acpi_get_table_ret(ACPI_SIG_PPTT, 0);
+
+ cpumask_clear(cpus);
+
+ if (IS_ERR(table))
+ return -ENOENT;
+
+ if (table->revision < 3)
+ return -ENOENT;
+
+ for_each_possible_cpu(cpu) {
+ acpi_cpu_id = get_acpi_id_for_cpu(cpu);
+ cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
+ if (WARN_ON_ONCE(!cpu_node))
+ continue;
+ num_levels = acpi_count_levels(table, cpu_node, NULL);
+
+ /* Start at 1 for L1 */
+ for (level = 1; level <= num_levels; level++) {
+ cache = acpi_find_cache_node(table, acpi_cpu_id,
+ ACPI_PPTT_CACHE_TYPE_UNIFIED,
+ level, &cpu_node);
+ if (!cache)
+ continue;
+
+ cache_v1 = ACPI_ADD_PTR(struct acpi_pptt_cache_v1,
+ cache,
+ sizeof(struct acpi_pptt_cache));
+
+ if (cache->flags & ACPI_PPTT_CACHE_ID_VALID &&
+ cache_v1->cache_id == cache_id)
+ cpumask_set_cpu(cpu, cpus);
+ }
+ }
+
+ return 0;
+}
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 5bdca5546697..c5fd92cda487 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 -EINVAL;
}
+static inline int acpi_pptt_get_cpumask_from_cache_id(u32 cache_id,
+ cpumask_t *cpus)
+{
+ return -ENOENT;
+}
#endif

void acpi_arch_init(void);
--
2.39.5