linux-kernel - Re: [PATCH 09/33] ACPI / MPAM: Parse the MPAM table

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Message-ID: <633d5c15-ffe1-4b52-a6aa-9a2c54e5fb98@arm.com>
Date: Thu, 13 Nov 2025 14:24:01 +0000
From: Ben Horgan <ben.horgan@....com>
To: Fenghua Yu <fenghuay@...dia.com>, james.morse@....com
Cc: amitsinght@...vell.com, baisheng.gao@...soc.com,
 baolin.wang@...ux.alibaba.com, bobo.shaobowang@...wei.com,
 carl@...amperecomputing.com, catalin.marinas@....com, dakr@...nel.org,
 dave.martin@....com, david@...hat.com, dfustini@...libre.com,
 gregkh@...uxfoundation.org, gshan@...hat.com, guohanjun@...wei.com,
 jeremy.linton@....com, jonathan.cameron@...wei.com, kobak@...dia.com,
 lcherian@...vell.com, lenb@...nel.org, linux-acpi@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 lpieralisi@...nel.org, peternewman@...gle.com, quic_jiles@...cinc.com,
 rafael@...nel.org, robh@...nel.org, rohit.mathew@....com,
 scott@...amperecomputing.com, sdonthineni@...dia.com, sudeep.holla@....com,
 tan.shaopeng@...itsu.com, will@...nel.org, xhao@...ux.alibaba.com,
 Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH 09/33] ACPI / MPAM: Parse the MPAM table

Hi Fenghua,

On 11/13/25 02:33, Fenghua Yu wrote:
> Hi, Ben and James,
> 
> On 11/7/25 04:34, Ben Horgan wrote:
>> From: James Morse <james.morse@....com>
> 
> [SNIP]
> 
>> +static int acpi_mpam_parse_resource(struct mpam_msc *msc,
>> +                    struct acpi_mpam_resource_node *res)
>> +{
>> +    int level, nid;
>> +    u32 cache_id;
>> +
>> +    switch (res->locator_type) {
>> +    case ACPI_MPAM_LOCATION_TYPE_PROCESSOR_CACHE:
>> +        cache_id = res->locator.cache_locator.cache_reference;
>> +        level = find_acpi_cache_level_from_id(cache_id);
>> +        if (level <= 0) {
>> +            pr_err_once("Bad level (%d) for cache with id %u\n",
>> level, cache_id);
>> +            return -EINVAL;
>> +        }
>> +        return mpam_ris_create(msc, res->ris_index, MPAM_CLASS_CACHE,
>> +                       level, cache_id);
>> +    case ACPI_MPAM_LOCATION_TYPE_MEMORY:
>> +        nid = pxm_to_node(res->locator.memory_locator.proximity_domain);
>> +        if (nid == NUMA_NO_NODE) {
>> +            pr_debug("Bad proxmity domain %lld, using node 0 instead\n",
>> +                 res->locator.memory_locator.proximity_domain);
>> +            nid = 0;
>> +        }
>> +        return mpam_ris_create(msc, res->ris_index, MPAM_CLASS_MEMORY,
>> +                       255, nid);
> 
> nit.
> 
> Seems "255" is an ad-hoc value which won't be used for memory type?
> The "class_id" in mpam_ris_create() is confused: it may be level for
> cache or it may be 255 for memory.
> 
> To be clearer, maybe it's better to define and enum for class_id?
> Something like:
> enum mpam_class_id {
>     CLASS_ID_LEVEL_1 = 1,
>     CLASS_ID_LEVEL_2,
>     CLASS_ID_LEVEL_3,
>     CLASS_ID_NOT_USED = 255  <--- for memory type
> };

I've added a new define, MPAM_CLASS_ID_DEFAULT, which can be used for
memory and anything else that only needs one class_id.

> 
> Thanks.
> 
> -Fenghua

-- 
Thanks,

Ben