On Fri, Aug 22, 2025 at 03:30:19PM +0000, James Morse wrote:
> acpi_count_levels() passes the number of levels back via a pointer argument.
> It also passes this to acpi_find_cache_level() as the starting_level, and
> preserves this value as it walks up the cpu_node tree counting the levels.
>
> This means the caller must initialise 'levels' due to acpi_count_levels()
> internals. The only caller acpi_get_cache_info() happens to have already
> initialised levels to zero, which acpi_count_levels() depends on to get the
> correct result.
>
> Two results are passed back from acpi_count_levels(), unlike split_levels,
> levels is not optional.
>
> Split these two results up. The mandatory 'levels' is always returned,
> which hides the internal details from the caller, and avoids having
> duplicated initialisation in all callers. split_levels remains an
> optional argument passed back.
>
> Suggested-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
>
> ---
> Changes since RFC:
> * Made acpi_count_levels() return the levels value.
> ---
> drivers/acpi/pptt.c | 18 +++++++++++-------
> 1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 4791ca2bdfac..8f9b9508acba 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -181,10 +181,10 @@ acpi_find_cache_level(struct acpi_table_header *table_hdr,
> * 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.
> + * success. Can be NULL.
Nit: tempting but this change does not belong here.
> *
> + * Returns 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 starting_level = 0;
> +
> do {
> - acpi_find_cache_level(table_hdr, cpu_node, levels, split_levels, 0, 0);
> + acpi_find_cache_level(table_hdr, cpu_node, &starting_level, split_levels, 0, 0);
> cpu_node = fetch_pptt_node(table_hdr, cpu_node->parent);
> } while (cpu_node);
> +
> + return starting_level;
> }
>
> /**
> @@ -731,7 +735,7 @@ 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);
Looks fine to me - though initializing
*levels = 0
upper in the function now becomes superfluous (?) (well, it initializes
*levels to 0 if an error path is hit but on that case the caller should
not expect *levels to be initialized to anything IIUC).
Apart from these (very) minor things:
Reviewed-by: Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx>
> pr_debug("Cache Setup: last_level=%d split_levels=%d\n",
> *levels, split_levels ? *split_levels : -1);
> --
> 2.20.1
>
