linux-kernel - Re: [RFC PATCH 07/36] ACPI / PPTT: Find cache level by cache-id

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Message-ID: <46248371-9a86-4653-8a06-4e1778808daa@arm.com>
Date: Tue, 5 Aug 2025 18:06:37 +0100
From: James Morse <james.morse@....com>
To: Ben Horgan <ben.horgan@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org
Cc: Rob Herring <robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
 Shanker Donthineni <sdonthineni@...dia.com>, Zeng Heng
 <zengheng4@...wei.com>, Lecopzer Chen <lecopzerc@...dia.com>,
 Carl Worth <carl@...amperecomputing.com>,
 shameerali.kolothum.thodi@...wei.com,
 D Scott Phillips OS <scott@...amperecomputing.com>, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
 Dave Martin <dave.martin@....com>, Koba Ko <kobak@...dia.com>,
 Sudeep Holla <sudeep.holla@....com>
Subject: Re: [RFC PATCH 07/36] ACPI / PPTT: Find cache level by cache-id

Hi Ben,

On 14/07/2025 12:42, Ben Horgan wrote:
> On 7/11/25 19:36, James Morse wrote:
>> The MPAM table identifies caches by id. The MPAM driver also wants to know
>> the cache level to determine if the platform is of the shape that can be
>> managed via resctrl. Cacheinfo has this information, but only for CPUs that
>> are online.
>>
>> Waiting for all CPUs to come online is a problem for platforms where
>> CPUs are brought online late by user-space.
>>
>> Add a helper that walks every possible cache, until it finds the one
>> identified by cache-id, then return the level.
>>
>> acpi_count_levels() expects its levels parameter to be initialised to
>> zero as it passes it to acpi_find_cache_level() as starting_level.
>> The existing callers do this. Document it.

> This paragraph is stale. You dealt with this in the previous commit.

Fixed, thanks.

James