linux-kernel - Re: [PATCH 02/33] drivers: base: cacheinfo: Add helper to find the cache size from cpu+level

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Message-ID: <aK7iDey7LATOXIUb@e133380.arm.com>
Date: Wed, 27 Aug 2025 11:46:37 +0100
From: Dave Martin <Dave.Martin@....com>
To: James Morse <james.morse@....com>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-acpi@...r.kernel.org, devicetree@...r.kernel.org,
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Subject: Re: [PATCH 02/33] drivers: base: cacheinfo: Add helper to find the
 cache size from cpu+level

Hi,

On Fri, Aug 22, 2025 at 03:29:43PM +0000, James Morse wrote:
> MPAM 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>
> 
> ---
> Changes since v1:
>  * Converted to kdoc.
>  * Simplified helper to use get_cpu_cacheinfo_level().
> ---
>  include/linux/cacheinfo.h | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
> index 2dcbb69139e9..e12d6f2c6a57 100644
> --- a/include/linux/cacheinfo.h
> +++ b/include/linux/cacheinfo.h
> @@ -148,6 +148,21 @@ static inline int get_cpu_cacheinfo_id(int cpu, int level)
>  	return ci ? ci->id : -1;
>  }
>  
> +/**
> + * get_cpu_cacheinfo_size() - Get the size of the cache.
> + * @cpu:      The cpu that is associated with the cache.
> + * @level:    The level of the cache as seen by @cpu.
> + *
> + * Callers must hold the cpuhp lock.
> + * Returns the cache-size on success, or 0 for an error.
> + */

Nit: Maybe use the wording

	cpuhp lock must be held.

in the kerneldoc here, to match the other helpers it sits alongside.

Otherwise, looks reasonable.

> +static inline unsigned int get_cpu_cacheinfo_size(int cpu, int level)
> +{
> +	struct cacheinfo *ci = get_cpu_cacheinfo_level(cpu, level);
> +
> +	return ci ? ci->size : 0;
> +}
> +

Orphaned function?

Can fs/resctrl/rdtgroup.c:rdtgroup_cbm_to_size() be ported to use this?
If so, this wouldn't just be dead code in this series.

Cheers
---Dave