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Message-ID: <094cc278-d488-4d22-a1f4-73616f4b99d5@nvidia.com>
Date: Wed, 1 Oct 2025 22:03:34 -0700
From: Fenghua Yu <fenghuay@...dia.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>,
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 04/29] ACPI / PPTT: Add a helper to fill a cpumask from
a cache_id
Hi, James,
On 9/10/25 13:42, 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.
>
> CC: Rohit Mathew <Rohit.Mathew@....com>
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Sudeep Holla <sudeep.holla@....com>
> ---
> Changes since v1:
> * Added punctuation to the commit message.
> * Removed a comment about an alternative implementaion.
> * Made the loop continue with a warning if a CPU is missing from the PPTT.
>
> Changes since RFC:
> * acpi_count_levels() now returns a value.
> * Converted the table-get stuff to use Jonathan's cleanup helper.
> * Dropped Sudeep's Review tag due to the cleanup change.
> ---
> drivers/acpi/pptt.c | 59 ++++++++++++++++++++++++++++++++++++++++++++
> include/linux/acpi.h | 6 +++++
> 2 files changed, 65 insertions(+)
>
> 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
> + * @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;
> + 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);
This function is almost identical to find_acpi_cache_level_from_id()
defined in patch #3.
To reduce code size and complexity, it's better to define a common
helper to server both of the two functions.
e.g. define a helper acpi_pptt_get_level_cpumask_from_cache_id(u32
cache_id, int *lvl, cpu_mask_t *cpus)
This helper has the same code body to traverse the cache levels for all
CPUs as find_acpi_cache_level_from_id() and
acpi_pptt_get_cpumask_from_cache_id(). The major difference is here:
+ if (cache->flags & ACPI_PPTT_CACHE_ID_VALID &&
+ cache_v1->cache_id == cache_id) {
+ if (cpus)
+ cpumask_set_cpu(cpu, cpus);
+ if ((level) {
+ *lvl = level;
+ return 0;
+ }
Then simplify the two callers as follows:
int find_acpi_cache_level_from_id(u32 cache_id)
{
int level;
int err = acpi_pptt_get_level_cpumask_from_cache_id(cache_id, &level, NULL);
if (err)
return err;
return level;
}
int acpi_pptt_get_cpumask_from_cache_id(u32 cache_id, cpumask_t *cpus)
{
return acpi_pptt_get_level_cpumask_from_cache_id(cache_id, NULL, cpus);
}
> + }
> + }
> +
> + return 0;
> +}
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 5bdca5546697..c5fd92cda487 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1543,6 +1543,7 @@ 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);
> int find_acpi_cache_level_from_id(u32 cache_id);
> +int acpi_pptt_get_cpumask_from_cache_id(u32 cache_id, cpumask_t *cpus);
> #else
> static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
> {
> @@ -1570,6 +1571,11 @@ 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 -ENOENT;
> +}
> #endif
>
> void acpi_arch_init(void);
Thanks.
-Fenghua
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