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

James Morse
2025-09-19T16:11:06Z

Hi Jonathan,

On 11/09/2025 12:06, Jonathan Cameron wrote:
> 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.

> 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.

I missed fixing this one up. That's done now.

>> 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.

I agree - the unified restriction turns out only to be of interest to archaeologists.
I've ripped it out.

>> + * @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;

I'm not sure why this one is a WARN_ON_ONCE() and the other isn't - both mean the PPTT
table is missing CPUs, but this looks like leftover debug. I'll drop it.

>> + 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.

Yup, I've done that in the previous one It's not otherwise done in this file - lets see if
someone cares strongly the other way.

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

Thanks,

James