linux-kernel - Re: [PATCH 4/5] cacheinfo: Expose the code to generate a cache-id from a device

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Message-ID: <d1756a25-97e2-4a3b-a3be-cb2d95cfb7c1@arm.com>
Date: Fri, 27 Jun 2025 17:38:44 +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 4/5] cacheinfo: Expose the code to generate a cache-id
 from a device_node

Hi Jonathan,

On 17/06/2025 17:21, Jonathan Cameron wrote:
> On Fri, 13 Jun 2025 13:03:55 +0000
> James Morse <james.morse@....com> wrote:

>> The MPAM driver identifies caches by id for use with resctrl. It
>> needs to know the cache-id when probe-ing, but the value isn't set
>> in cacheinfo until the corresponding CPU comes online.
>>
>> Expose the code that generates the cache-id. This allows the MPAM
>> driver to determine the properties of the caches without waiting
>> for all CPUs to come online.

> Feels to me like this needs to come with the user.
> The earlier patches at least expose it via existing infrastructure
> this isn't used at all yet...

Yeah, I'm damned whatever I do here. I can move this (and patch 5) to the series with the
MPAM driver - this was me trying to reduce the number of people that get copied on that,
and the number of trees that it touches...

>> diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
>> index d8e5b4c7156c..6316d80abab8 100644
>> --- a/drivers/base/cacheinfo.c
>> +++ b/drivers/base/cacheinfo.c
>> @@ -188,7 +188,7 @@ static bool cache_node_is_unified(struct cacheinfo *this_leaf,
>>  #define arch_compact_of_hwid(_x)	(_x)
>>  #endif
>>  
>> -static void cache_of_set_id(struct cacheinfo *this_leaf, struct device_node *np)
>> +unsigned long cache_of_get_id(struct device_node *np)

> Bit confusing to have cache_of_set_id() call cache_of_get_id() like this because
> they are in no way mirrors of each other.   Rename?
> (and naturally I'm providing no suggestions :)

I'll try cache_of_calculate_id() ...

>>  {
>>  	struct device_node *cpu;
>>  	u32 min_id = ~0;

Thanks,

James