linux-kernel - Re: [PATCH v3 04/29] ACPI / PPTT: Add a helper to fill a cpumask from a cache

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Message-ID: <12556653-a26f-4c28-820a-4b5ba1537bc4@arm.com>
Date: Mon, 20 Oct 2025 11:45:33 +0100
From: Ben Horgan <ben.horgan@....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>, Jeremy Linton <jeremy.linton@....com>,
 Gavin Shan <gshan@...hat.com>
Subject: Re: [PATCH v3 04/29] ACPI / PPTT: Add a helper to fill a cpumask from
 a cache_id

Hi James,

On 10/17/25 19:56, 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>
> Tested-by: Fenghua Yu <fenghuay@...dia.com>
> ---
> Changes since v2:
>  * Removed stray cleanup useage in preference for acpi_get_pptt().
>  * Removed WARN_ON_ONCE() for symmetry with other helpers.
>  * Dropped restriction on unified caches.
> 
> 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  | 64 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/acpi.h |  6 +++++
>  2 files changed, 70 insertions(+)
> 
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 50c8f2a3c927..2f86f58699a6 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -985,3 +985,67 @@ 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 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)
> +{
> +	int level, cpu;
> +	u32 acpi_cpu_id;
> +	struct acpi_pptt_cache *cache;
> +	struct acpi_table_header *table;
> +	struct acpi_pptt_cache_v1 *cache_v1;
> +	struct acpi_pptt_processor *cpu_node;
> +
> +	cpumask_clear(cpus);
> +
> +	table = acpi_get_pptt();
> +	if (!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 (!cpu_node)
> +			continue;
> +
> +		/* Start at 1 for L1 */
> +		level = 1;
> +		cache = acpi_find_any_type_cache_node(table, acpi_cpu_id, level,
> +						      &cpu_node);
> +		while (cache) {
> +			cache_v1 = ACPI_ADD_PTR(struct acpi_pptt_cache_v1,
> +						cache, sizeof(*cache));
> +			if (!cache)
> +				continue;
> +
> +			cache_v1 = ACPI_ADD_PTR(struct acpi_pptt_cache_v1,
> +						cache, sizeof(*cache));
> +
> +			if (cache->flags & ACPI_PPTT_CACHE_ID_VALID &&
> +			    cache_v1->cache_id == cache_id)
> +				cpumask_set_cpu(cpu, cpus);
> +
> +			level++;

Same comment as for the previous patch. You are bumping the level
without considering if there is another cache at that level.

> +			cache = acpi_find_any_type_cache_node(table, acpi_cpu_id,
> +							      level, &cpu_node);
> +		}
> +	}
> +
> +	return 0;
> +}
Thanks,

Ben