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From:   "tarumizu.kohei@fujitsu.com" <tarumizu.kohei@fujitsu.com>
To:     'Sudeep Holla' <sudeep.holla@arm.com>
CC:     "catalin.marinas@arm.com" <catalin.marinas@arm.com>,
        "will@kernel.org" <will@kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>, "hpa@zytor.com" <hpa@zytor.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 5/8] arm64: Create cache sysfs directory without ACPI PPTT
 for hardware prefetch control
Thread-Topic: [PATCH 5/8] arm64: Create cache sysfs directory without ACPI
 PPTT for hardware prefetch control
Thread-Index: AQHYEbs2rD8REiPg/U+HaUWHy1epU6x1HZ8AgAmD11A=
Date:   Tue, 1 Feb 2022 11:56:59 +0000
Message-ID: <OSBPR01MB2037E92722D372D48F54438E80269@OSBPR01MB2037.jpnprd01.prod.outlook.com>
References: <20220125071414.811344-1-tarumizu.kohei@fujitsu.com>
 <20220125071414.811344-6-tarumizu.kohei@fujitsu.com>
 <20220126103614.pcrcuc2kzklkq3xa@bogus>
In-Reply-To: <20220126103614.pcrcuc2kzklkq3xa@bogus>
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> 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 registe=
rs from
> UEFI/EDK2 as PPTT has other topology information which you will need anyw=
ays.
> 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.