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

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Message-ID: <OSBPR01MB2037E92722D372D48F54438E80269@OSBPR01MB2037.jpnprd01.prod.outlook.com>
Date:   Tue, 1 Feb 2022 11:56:59 +0000
From:   "tarumizu.kohei@...itsu.com" <tarumizu.kohei@...itsu.com>
To:     'Sudeep Holla' <sudeep.holla@....com>
CC:     "catalin.marinas@....com" <catalin.marinas@....com>,
        "will@...nel.org" <will@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 5/8] arm64: Create cache sysfs directory without ACPI PPTT
 for hardware prefetch control

> I am assuming this is ACPI enabled system.

Yes, it 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 ?

The latest firmware of ARM64 machine, FX700 with the A64FX processor
does not support PPTT.
I think adding PPTT is the best way to generate cacheinfo sysfs.
However, it is difficult to modify the firmware to add PPTT, so
it is not clear when it will be possible.
Therefore, I would like to implement the function in the kernel on
the condition that firmware does not support PPTT.