linux-kernel - Re: [PATCH v3 02/29] ACPI / PPTT: Stop acpi_count_levels() expecting callers to clear levels

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Message-ID: <20251024122921.000004bc@huawei.com>
Date: Fri, 24 Oct 2025 12:29:21 +0100
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: James Morse <james.morse@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-acpi@...r.kernel.org>, D Scott Phillips OS
	<scott@...amperecomputing.com>, <carl@...amperecomputing.com>,
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 Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
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	<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 02/29] ACPI / PPTT: Stop acpi_count_levels()
 expecting callers to clear levels

On Fri, 17 Oct 2025 18:56:18 +0000
James Morse <james.morse@....com> wrote:

> 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@...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>
> Tested-by: Fenghua Yu <fenghuay@...dia.com>

Another meh, the name is confusing type comment. 

> -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;
Given it's not the starting level at this point... Maybe just call it level or 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);