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

Jonathan Cameron
2025-09-11T11:06:19Z

On Wed, 10 Sep 2025 20:42:44 +0000
James Morse <james.morse@arm.com> wrote:

> 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.

Why for this case does it makes sense to not just use acpi_get_pptt()?

Also you don't introduce the acpi_get_table_reg() helper until patch 6.

> * 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

Similar comment to previous patch. If we are going to make this unified only
can we reflect that in the function name. I worry this will get reused
and that restriction will surprise.

> + * @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));

sizeof(*cache) makes more sense to me.

> +
> + if (cache->flags & ACPI_PPTT_CACHE_ID_VALID &&
> + cache_v1->cache_id == cache_id)
> + cpumask_set_cpu(cpu, cpus);
> + }
> + }
> +
> + return 0;
> +}