linux-kernel - Re: [PATCH v2 03/29] ACPI / PPTT: Find cache level by cache-id

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Message-ID: <81262452-d780-4e85-b153-b3b8d16eabae@redhat.com>
Date: Fri, 3 Oct 2025 10:23:26 +1000
From: Gavin Shan <gshan@...hat.com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org
Cc: D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...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>, Dave Martin <dave.martin@....com>,
 Koba Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 fenghuay@...dia.com, baisheng.gao@...soc.com,
 Jonathan Cameron <jonathan.cameron@...wei.com>, Rob Herring
 <robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
 Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
 <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v2 03/29] ACPI / PPTT: Find cache level by cache-id

On 9/11/25 6:42 AM, 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.
> 
> Signed-off-by: James Morse <james.morse@....com>
> ---
> Changes since v1:
>   * Droppeed the cleanup based table freeing, use acpi_get_pptt() instead.
>   * Removed a confusing comment.
>   * Clarified the kernel doc.
> 
> Changes since RFC:
>   * acpi_count_levels() now returns a value.
>   * Converted the table-get stuff to use Jonathan's cleanup helper.
>   * Dropped Sudeep's Review tag due to the cleanup change.
> ---
>   drivers/acpi/pptt.c  | 62 ++++++++++++++++++++++++++++++++++++++++++++
>   include/linux/acpi.h |  5 ++++
>   2 files changed, 67 insertions(+)
> 

With existing comments addressed, especially those from Lorenzo Pieralisi:

Reviewed-by: Gavin Shan <gshan@...hat.com>