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

Jonathan Cameron
2025-11-10T16:04:46Z

On Fri, 7 Nov 2025 12:34:22 +0000
Ben Horgan <ben.horgan@arm.com> wrote:

> 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>

Very similar comments to on previous.

> ---
> 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;

Basically same comments. This dance of setting it not_empty to
get into the loop is a bit nasty as it means that variable is
briefly has an alternative meaning the name doesn't convey.

A do/while() doesn't have that problem as we always do one iteration.

> + 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;
> +}