linux-kernel - Re: [PATCH v6 02/34] ACPI / PPTT: Stop acpi_count_levels() expecting callers to clear levels

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Message-ID: <a3f76eb4-b128-4930-aff2-1d410cd00df1@arm.com>
Date: Wed, 19 Nov 2025 11:08:35 -0600
From: Jeremy Linton <jeremy.linton@....com>
To: Ben Horgan <ben.horgan@....com>, james.morse@....com
Cc: amitsinght@...vell.com, baisheng.gao@...soc.com,
 baolin.wang@...ux.alibaba.com, bobo.shaobowang@...wei.com,
 carl@...amperecomputing.com, catalin.marinas@....com, dakr@...nel.org,
 dave.martin@....com, david@...hat.com, dfustini@...libre.com,
 fenghuay@...dia.com, gregkh@...uxfoundation.org, gshan@...hat.com,
 guohanjun@...wei.com, jonathan.cameron@...wei.com, kobak@...dia.com,
 lcherian@...vell.com, lenb@...nel.org, linux-acpi@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 lpieralisi@...nel.org, peternewman@...gle.com, quic_jiles@...cinc.com,
 rafael@...nel.org, robh@...nel.org, rohit.mathew@....com,
 scott@...amperecomputing.com, sdonthineni@...dia.com, sudeep.holla@....com,
 tan.shaopeng@...itsu.com, will@...nel.org, xhao@...ux.alibaba.com,
 reinette.chatre@...el.com, Shaopeng Tan <tan.shaopeng@...fujitsu.com>,
 Zeng Heng <zengheng4@...wei.com>
Subject: Re: [PATCH v6 02/34] ACPI / PPTT: Stop acpi_count_levels() expecting
 callers to clear levels

On 11/19/25 6:22 AM, Ben Horgan wrote:
> From: James Morse <james.morse@....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.

Per V5:

Reviewed-by: Jeremy Linton <jeremy.linton@....com>>
> Suggested-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Lorenzo Pieralisi <lpieralisi@...nel.org>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> Reviewed-by: Fenghua Yu <fenghuay@...dia.com>
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
> Reviewed-by: Hanjun Guo <guohanjun@...wei.com>
> Tested-by: Fenghua Yu <fenghuay@...dia.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
> Tested-by: Peter Newman <peternewman@...gle.com>
> Tested-by: Carl Worth <carl@...amperecomputing.com>
> Tested-by: Gavin Shan <gshan@...hat.com>
> Tested-by: Zeng Heng <zengheng4@...wei.com>
> Tested-by: Hanjun Guo <guohanjun@...wei.com>
> Signed-off-by: Ben Horgan <ben.horgan@....com>
> ---
> 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 b8248c0092fe..2856254e29d7 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);