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Message-ID: <3a2f6807-9a49-4976-a4d7-7577756c3c26@redhat.com>
Date: Fri, 3 Oct 2025 10:15:04 +1000
From: Gavin Shan <gshan@...hat.com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org
Cc: D Scott Phillips OS <scott@...amperecomputing.com>,
carl@...amperecomputing.com, lcherian@...vell.com,
bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
dfustini@...libre.com, amitsinght@...vell.com,
David Hildenbrand <david@...hat.com>, Dave Martin <dave.martin@....com>,
Koba Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
fenghuay@...dia.com, baisheng.gao@...soc.com,
Jonathan Cameron <jonathan.cameron@...wei.com>, Rob Herring
<robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
<guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v2 01/29] ACPI / PPTT: Add a helper to fill a cpumask from
a processor container
On 9/11/25 6:42 AM, 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@....com>
> Reviewed-by: Sudeep Holla <sudeep.holla@....com>
> Signed-off-by: James Morse <james.morse@....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(+)
>
With the description for the return value of acpi_pptt_get_cpus_from_container()
is dropped since that function doesn't have a return value, as mentioned by
Stanimir Varbanov.
Reviewed-by: Gavin Shan <gshan@...hat.com>
Thanks,
Gavin
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 54676e3d82dd..1728545d90b2 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -817,3 +817,86 @@ int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
> return find_acpi_cpu_topology_tag(cpu, PPTT_ABORT_PACKAGE,
> ACPI_PPTT_ACPI_IDENTICAL);
> }
> +
> +/**
> + * 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 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.
> + */
> +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;
> + unsigned long table_end;
> + u32 proc_sz;
> +
> + cpumask_clear(cpus);
> +
> + table_hdr = acpi_get_pptt();
> + if (!table_hdr)
> + return;
> +
> + 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) {
> + if (!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);
> + break;
> + }
> + }
> + }
> + entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry,
> + entry->length);
> + }
> +}
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 1c5bb1e887cd..f97a9ff678cc 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);
> +void 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 +1563,8 @@ static inline int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
> {
> return -EINVAL;
> }
> +static inline void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id,
> + cpumask_t *cpus) { }
> #endif
>
> void acpi_arch_init(void);
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