Re: [PATCH v2 01/29] ACPI / PPTT: Add a helper to fill a cpumask from a processor container

Stanimir Varbanov
2025-09-25T09:33:05Z

Hi James,

On 9/10/25 11:42 PM, James Morse wrote:
> The ACPI MPAM table uses the UID of a processor container specified in
> the PPTT to indicate the subset of CPUs and cache topology that can
> access each MPAM System Component (MSC).
>
> This information is not directly useful to the kernel. The equivalent
> cpumask is needed instead.
>
> Add a helper to find the processor container by its id, then walk
> the possible CPUs to fill a cpumask with the CPUs that have this
> processor container as a parent.
>
> CC: Dave Martin <dave.martin@arm.com>
> Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v1:
> * Replaced commit message with wording from Dave.
> * Fixed a stray plural.
> * Moved further down in the file to make use of get_pptt() helper.
> * Added a break to exit the loop early.
>
> Changes since RFC:
> * Removed leaf_flag local variable from acpi_pptt_get_cpus_from_container()
>
> Changes since RFC:
> * Dropped has_leaf_flag dodging of acpi_pptt_leaf_node()
> * Added missing : in kernel-doc
> * Made helper return void as this never actually returns an error.
> ---
> drivers/acpi/pptt.c | 83 ++++++++++++++++++++++++++++++++++++++++++++
> include/linux/acpi.h | 3 ++
> 2 files changed, 86 insertions(+)
>

<snip>

> +
> +/**
> + * acpi_pptt_get_cpus_from_container() - Populate a cpumask with all CPUs in a
> + * processor container
> + * @acpi_cpu_id: The UID of the processor container.
> + * @cpus: The resulting CPU mask.
> + *
> + * Find the specified Processor Container, and fill @cpus with all the cpus
> + * below it.
> + *
> + * Not all 'Processor' entries in the PPTT are either a CPU or a Processor
> + * Container, they may exist purely to describe a Private resource. CPUs
> + * have to be leaves, so a Processor Container is a non-leaf that has the
> + * 'ACPI Processor ID valid' flag set.
> + *
> + * Return: 0 for a complete walk, or an error if the mask is incomplete.

Leftover, drop this.

> + */
> +void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus)
> +{
> + struct acpi_pptt_processor *cpu_node;
> + struct acpi_table_header *table_hdr;
> + struct acpi_subtable_header *entry;

<snip>

regards,
~Stan