linux-kernel - Re: [PATCH 5/5] cacheinfo: Add helper to find the cache size from cpu+level

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Message-ID: <20250617172808.00005c14@huawei.com>
Date: Tue, 17 Jun 2025 17:28:08 +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>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, "Rafael J . Wysocki"
	<rafael@...nel.org>, <sudeep.holla@....com>, Rob Herring <robh@...nel.org>,
	Ben Horgan <ben.horgan@....com>
Subject: Re: [PATCH 5/5] cacheinfo: Add helper to find the cache size from
 cpu+level

On Fri, 13 Jun 2025 13:03:56 +0000
James Morse <james.morse@....com> wrote:

> The MPAM driver needs to know the size of a cache associated with a
> particular CPU. The DT/ACPI agnostic way of doing this is to ask cacheinfo.
> 
> Add a helper to do this.
> 
> Signed-off-by: James Morse <james.morse@....com>



> ---
>  include/linux/cacheinfo.h | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
> index 9c959caf8af8..3f1b6b2e25b5 100644
> --- a/include/linux/cacheinfo.h
> +++ b/include/linux/cacheinfo.h
> @@ -148,6 +148,26 @@ static inline int get_cpu_cacheinfo_id(int cpu, int level)
>  	return ci ? ci->id : -1;
>  }
>  
> +/*
> + * Get the size of the cache associated with @cpu at level @level.
> + * cpuhp lock must be held.
To me kernel-doc would be appropriate.  Particularly the return 0 thing.
However there isn't any for existing cacheinfo interfaces so maybe
fair enough to 'follow local style' on that.

> + */
> +static inline unsigned int get_cpu_cacheinfo_size(int cpu, int level)
> +{
> +	struct cpu_cacheinfo *ci = get_cpu_cacheinfo(cpu);
> +	int i;
> +
> +	if (!ci->info_list)
> +		return 0;
> +
> +	for (i = 0; i < ci->num_leaves; i++) {
> +		if (ci->info_list[i].level == level)
> +			return ci->info_list[i].size;
> +	}
> +
> +	return 0;
> +}
> +
Why not

static inline unsigned int get_cpu_cacheinfo_size(int cpu, int level)
{
	struct cpu_cachinfo *ci = get_cpu_cacheinfo_level(cpu, lev);

	return ci ? ci->size; 0;
}

Like existing get_cpu_cacheinfo_id()?

>  #if defined(CONFIG_ARM64) || defined(CONFIG_ARM)
>  #define use_arch_cache_info()	(true)
>  #else