linux-kernel - Re: [PATCH 5/8] arm64: Create cache sysfs directory without ACPI PPTT for hardware prefetch control

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Date:   Wed, 26 Jan 2022 10:36:14 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Kohei Tarumizu <tarumizu.kohei@...itsu.com>
Cc:     catalin.marinas@....com, will@...nel.org, tglx@...utronix.de,
        Sudeep Holla <sudeep.holla@....com>, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] arm64: Create cache sysfs directory without ACPI
 PPTT for hardware prefetch control

On Tue, Jan 25, 2022 at 04:14:11PM +0900, Kohei Tarumizu wrote:
> This patch will create a cache sysfs directory without ACPI PPTT if
> the CONFIG_HWPF_CONTROL is true.
> 
> Hardware prefetch control driver need cache sysfs directory and cache
> level/type information. In ARM processor, these information can be
> obtained from the register even without PPTT. Therefore, we set the
> cpu_map_populated to true to create cache sysfs directory if the
> machine doesn't have PPTT.

I am assuming this is ACPI enabled system.

This looks bit hacky in my opinion. Before I explore better way of adding it,
I would like to check if you have explored ways to add PPTT reading these
registers from UEFI/EDK2 as PPTT has other topology information which you will
need anyways. That would simplify handling of these cacheinfo sysfs in the
kernel. Let me know what are your thoughts ?

-- 
Regards,
Sudeep