RE: [PATCH 02/33] ACPI / PPTT: Stop acpi_count_levels() expecting callers to clear levels

Shaopeng Tan (Fujitsu)
2025-11-11T07:34:19Z

Hello Ben,

> From: James Morse <james.morse@arm.com>
>
> In acpi_count_levels(), the initial value of *levels passed by the caller is really
> an implementation detail of acpi_count_levels(), so it is unreasonable to
> expect the callers of this function to know what to pass in for this parameter.
> The only sensible initial value is 0, which is what the only upstream caller
> (acpi_get_cache_info()) passes.
>
> Use a local variable for the starting cache level in acpi_count_levels(), and pass
> the result back to the caller via the function return value.
>
> Get rid of the levels parameter, which has no remaining purpose.
>
> Fix acpi_get_cache_info() to match.
>
> Suggested-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> Reviewed-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
> Tested-by: Fenghua Yu <fenghuay@nvidia.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
> Tested-by: Peter Newman <peternewman@google.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
"Reviewed-by" and "Tested-by" are mixed together.
It would be better to group them.
(Not just in this patch, but in other patches as well.)

Best regards,
Shaopeng TAN

> Changes since v3:
> s/starting_level/current_level/ (Jonathan)
> ---
> drivers/acpi/pptt.c | 20 ++++++++++++--------
> 1 file changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c index
> 69917cc6bd2f..1027ca3566b1 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -177,14 +177,14 @@ acpi_find_cache_level(struct acpi_table_header
> *table_hdr, }
>
> /**
> - * acpi_count_levels() - Given a PPTT table, and a CPU node, count the cache
> - * levels and split cache levels (data/instruction).
> + * acpi_count_levels() - Given a PPTT table, and a CPU node, count the
> + * total number of levels and split cache levels (data/instruction).
> * @table_hdr: Pointer to the head of the PPTT table
> * @cpu_node: processor node we wish to count caches for
> - * @levels: Number of levels if success.
> * @split_levels: Number of split cache levels (data/instruction) if
> * success. Can by NULL.
> *
> + * Return: number of levels.
> * Given a processor node containing a processing unit, walk into it and count
> * how many levels exist solely for it, and then walk up each level until we hit
> * the root node (ignore the package level because it may be possible to have
> @@ -192,14 +192,18 @@ acpi_find_cache_level(struct acpi_table_header
> *table_hdr,
> * split cache levels (data/instruction) that exist at each level on the way
> * up.
> */
> -static void acpi_count_levels(struct acpi_table_header *table_hdr,
> - struct acpi_pptt_processor *cpu_node,
> - unsigned int *levels, unsigned int *split_levels)
> +static int acpi_count_levels(struct acpi_table_header *table_hdr,
> + struct acpi_pptt_processor *cpu_node,
> + unsigned int *split_levels)
> {
> + int current_level = 0;
> +
> do {
> - acpi_find_cache_level(table_hdr, cpu_node, levels,
> split_levels, 0, 0);
> + acpi_find_cache_level(table_hdr, cpu_node, &current_level,
> +split_levels, 0, 0);
> cpu_node = fetch_pptt_node(table_hdr, cpu_node->parent);
> } while (cpu_node);
> +
> + return current_level;
> }
>
> /**
> @@ -645,7 +649,7 @@ int acpi_get_cache_info(unsigned int cpu, unsigned int
> *levels,
> if (!cpu_node)
> return -ENOENT;
>
> - acpi_count_levels(table, cpu_node, levels, split_levels);
> + *levels = acpi_count_levels(table, cpu_node, split_levels);
>
> pr_debug("Cache Setup: last_level=%d split_levels=%d\n",
> *levels, split_levels ? *split_levels : -1);
> --
> 2.43.0