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

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Message-ID: <88e4005e-64d3-4019-939f-5c0c656666ca@arm.com>
Date: Fri, 27 Jun 2025 17:38:39 +0100
From: James Morse <james.morse@....com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.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

Hi Jonathan,

On 17/06/2025 17:28, Jonathan Cameron wrote:
> 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.

>> 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.

Documentation should be the direction of travel right? I'll change this.

>> + */
>> +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()?

I've been dragging this around for years. Fixed.

Thanks!

James