Hi Lorenzo,
On 10/09/2025 17:06, Lorenzo Pieralisi wrote:
> On Fri, Aug 22, 2025 at 03:30:21PM +0000, James Morse 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.
>> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
>> index 660457644a5b..cb93a9a7f9b6 100644
>> --- a/drivers/acpi/pptt.c
>> +++ b/drivers/acpi/pptt.c
>> @@ -971,3 +971,65 @@ 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 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;
>> +
>> + /*
>> + * If we found the cache first, we'd still need to walk from each cpu.
>> + */
>> + 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 0;
>
> If for a possible cpu you don't get an acpi_pptt_processor node we return 0,
> is that correct ? Should not the loop continue ? Forgive me if that's a
> dumb question.
That looks like me throwing my hands up in the air and bailing out!
Yes, the loop continue-ing would be better as only possible CPUs that are missing a
PPTT description (...and cache hierarchy...) would be missing form the bitmap.
It's probably worth a WARN_ON_ONCE() too.
Thanks for spotting that!
>> + 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 30c10b1dcdb2..4ad08f5f1d83 100644
>> --- a/include/linux/acpi.h
>> +++ b/include/linux/acpi.h
>> @@ -1555,6 +1555,7 @@ int find_acpi_cpu_topology_package(unsigned int cpu);
>> @@ -1582,6 +1583,11 @@ 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 -EINVAL;
>
> Nit: You might want the return value here to be coherent with what the function
> documentation states (ie return -ENOENT;)
Makes sense,
> Other than that:
>
> Reviewed-by: Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx>
Thanks!
James
