Re: [RFC PATCH 05/36] ACPI / PPTT: Add a helper to fill a cpumask from a processor container

[Ben Horgan <ben.horgan@arm.com>]

Hi James,

On 7/11/25 19:36, James Morse wrote:
> The PPTT describes CPUs and caches, as well as processor containers.
> The ACPI table for MPAM describes the set of CPUs that can access an MSC
> with the UID of a processor container.
> 
> 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>
> ---
>   drivers/acpi/pptt.c  | 93 ++++++++++++++++++++++++++++++++++++++++++++
>   include/linux/acpi.h |  6 +++
>   2 files changed, 99 insertions(+)
> 
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 54676e3d82dd..13619b1b821b 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -298,6 +298,99 @@ static struct acpi_pptt_processor *acpi_find_processor_node(struct acpi_table_he
>   	return NULL;
>   }
>   
> +/**
> + * acpi_pptt_get_child_cpus() - Find all the CPUs below a PPTT processor node
> + * @table_hdr:		A reference to the PPTT table.
> + * @parent_node:	A pointer to the processor node in the @table_hdr.
> + * @cpus:		A cpumask to fill with the CPUs below @parent_node.
> + *
> + * Walks up the PPTT from every possible CPU to find if the provided
> + * @parent_node is a parent of this CPU.
> + */
> +static void acpi_pptt_get_child_cpus(struct acpi_table_header *table_hdr,
> +				     struct acpi_pptt_processor *parent_node,
> +				     cpumask_t *cpus)
> +{
> +	struct acpi_pptt_processor *cpu_node;
> +	u32 acpi_id;
> +	int cpu;
> +
> +	cpumask_clear(cpus);
> +
> +	for_each_possible_cpu(cpu) {
> +		acpi_id = get_acpi_id_for_cpu(cpu);
> +		cpu_node = acpi_find_processor_node(table_hdr, acpi_id);
> +
> +		while (cpu_node) {
> +			if (cpu_node == parent_node) {
> +				cpumask_set_cpu(cpu, cpus);
> +				break;
> +			}
> +			cpu_node = fetch_pptt_node(table_hdr, cpu_node->parent);
> +		}
> +	}
> +}
> +
> +/**
> + * acpi_pptt_get_cpus_from_container() - Populate a cpumask with all CPUs in a
> + *                                       processor containers
> + * @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.
> + */
> +int 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;
> +	bool leaf_flag, has_leaf_flag = false;
> +	unsigned long table_end;
> +	acpi_status status;
> +	u32 proc_sz;
> +	int ret = 0;
> +
> +	cpumask_clear(cpus);
> +
> +	status = acpi_get_table(ACPI_SIG_PPTT, 0, &table_hdr);
> +	if (ACPI_FAILURE(status))
> +		return 0;
> +
> +	if (table_hdr->revision > 1)
> +		has_leaf_flag = true;
> +
> +	table_end = (unsigned long)table_hdr + table_hdr->length;
> +	entry = ACPI_ADD_PTR(struct acpi_subtable_header, table_hdr,
> +			     sizeof(struct acpi_table_pptt));
> +	proc_sz = sizeof(struct acpi_pptt_processor);
> +	while ((unsigned long)entry + proc_sz <= table_end) {
> +		cpu_node = (struct acpi_pptt_processor *)entry;
> +		if (entry->type == ACPI_PPTT_TYPE_PROCESSOR &&
> +		    cpu_node->flags & ACPI_PPTT_ACPI_PROCESSOR_ID_VALID) {
> +			leaf_flag = cpu_node->flags & ACPI_PPTT_ACPI_LEAF_NODE;
> +			if ((has_leaf_flag && !leaf_flag) ||
> +			    (!has_leaf_flag && !acpi_pptt_leaf_node(table_hdr, cpu_node))) {
> +				if (cpu_node->acpi_processor_id == acpi_cpu_id)
> +					acpi_pptt_get_child_cpus(table_hdr, cpu_node, cpus);
> +			}
acpi_pptt_leaf_node() returns early based on the leaf flag so you can 
just rely on that here; remove has_leaf_flag and the corresponding extra 
logic.
> +		}
> +		entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry,
> +				     entry->length);
> +	}
> +
> +	acpi_put_table(table_hdr);
> +
> +	return ret;
> +}
> +
>   static u8 acpi_cache_type(enum cache_type type)
>   {
>   	switch (type) {
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index f102c0fe3431..8c3165c2b083 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1541,6 +1541,7 @@ int find_acpi_cpu_topology(unsigned int cpu, int level);
>   int find_acpi_cpu_topology_cluster(unsigned int cpu);
>   int find_acpi_cpu_topology_package(unsigned int cpu);
>   int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
> +int acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus);
>   #else
>   static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
>   {
> @@ -1562,6 +1563,11 @@ static inline int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
>   {
>   	return -EINVAL;
>   }
> +static inline int acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id,
> +						    cpumask_t *cpus)
> +{
> +	return -EINVAL;
> +}
>   #endif
>   
>   void acpi_arch_init(void);


Thanks,

Ben