Hi James,
On 8/22/25 16:29, James Morse wrote:
> The MPAM table identifies caches by id. The MPAM driver also wants to know
> the cache level to determine if the platform is of the shape that can be
> managed via resctrl. Cacheinfo has this information, but only for CPUs that
> are online.
>
> Waiting for all CPUs to come online is a problem for platforms where
> CPUs are brought online late by user-space.
>
> Add a helper that walks every possible cache, until it finds the one
> identified by cache-id, then return the level.
> Add a cleanup based free-ing mechanism for acpi_get_table().
>
> CC: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> ---
> 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 | 64 ++++++++++++++++++++++++++++++++++++++++++++
> include/linux/acpi.h | 17 ++++++++++++
> 2 files changed, 81 insertions(+)
>
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 8f9b9508acba..660457644a5b 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -907,3 +907,67 @@ int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
> return find_acpi_cpu_topology_tag(cpu, PPTT_ABORT_PACKAGE,
> ACPI_PPTT_ACPI_IDENTICAL);
> }
> +
> +/**
> + * find_acpi_cache_level_from_id() - Get the level of the specified cache
> + * @cache_id: The id field of the unified cache
> + *
> + * Determine the level relative to any CPU for the unified cache identified by
> + * cache_id. This allows the property to be found even if the CPUs are offline.
> + *
> + * The returned level can be used to group unified caches that are peers.
> + *
> + * The PPTT table must be rev 3 or later,
> + *
> + * If one CPUs L2 is shared with another as L3, this function will return
> + * an unpredictable value.
> + *
> + * Return: -ENOENT if the PPTT doesn't exist, or the cache cannot be found.
> + * Otherwise returns a value which represents the level of the specified cache.
> + */
> +int find_acpi_cache_level_from_id(u32 cache_id)
> +{
> + 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);
> +
> + if (IS_ERR(table))
> + return PTR_ERR(table);
> +
> + if (table->revision < 3)
> + return -ENOENT;
> +
> + /*
> + * If we found the cache first, we'd still need to walk from each CPU
> + * to find the level...
> + */
> + 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 (!cpu_node)
> + return -ENOENT;
> + 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)
> + return level;
> + }
> + }
> +
> + return -ENOENT;
> +}
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index f97a9ff678cc..30c10b1dcdb2 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -8,6 +8,7 @@
> #ifndef _LINUX_ACPI_H
> #define _LINUX_ACPI_H
>
> +#include <linux/cleanup.h>
> #include <linux/errno.h>
> #include <linux/ioport.h> /* for struct resource */
> #include <linux/resource_ext.h>
> @@ -221,6 +222,17 @@ void acpi_reserve_initial_tables (void);
> void acpi_table_init_complete (void);
> int acpi_table_init (void);
>
> +static inline struct acpi_table_header *acpi_get_table_ret(char *signature, u32 instance)
> +{
> + struct acpi_table_header *table;
> + int status = acpi_get_table(signature, instance, &table);
> +
> + if (ACPI_FAILURE(status))
> + return ERR_PTR(-ENOENT);
> + return table;
> +}
> +DEFINE_FREE(acpi_table, struct acpi_table_header *, if (!IS_ERR(_T)) acpi_put_table(_T))
nit: Is it useful to change the condition from !IS_ERR(_T) to
!IS_ERR_OR_NULL(_T)? This seems to be the common pattern. I do note that
acpi_put_table() can take NULL, so there is no real danger.
> +
> int acpi_table_parse(char *id, acpi_tbl_table_handler handler);
> int __init_or_acpilib acpi_table_parse_entries(char *id,
> unsigned long table_size, int entry_id,
> @@ -1542,6 +1554,7 @@ int find_acpi_cpu_topology_cluster(unsigned int cpu);
> 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);
> #else
> static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
> {
> @@ -1565,6 +1578,10 @@ static inline int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
> }
> static inline void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id,
> cpumask_t *cpus) { }
> +static inline int find_acpi_cache_level_from_id(u32 cache_id)
> +{
> + return -EINVAL;
> +}
> #endif
>
> void acpi_arch_init(void);
Thanks,
Ben
