linux-kernel - Re: [PATCH v2 3/8] arm64: Add hardware prefetch control support for ARM64

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Date:   Wed, 30 Mar 2022 17:11:50 -0500
From:   Rob Herring <robh@...nel.org>
To:     Kohei Tarumizu <tarumizu.kohei@...itsu.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/8] arm64: Add hardware prefetch control support for ARM64

On Fri, Mar 11, 2022 at 4:23 AM Kohei Tarumizu
<tarumizu.kohei@...itsu.com> wrote:
>
> This adds module init/exit code, and creates sysfs attribute files for
> "stream_detect_prefetcher_enable", "stream_detect_prefetcher_strong"
> and "stream_detect_prefetcher_dist". This driver works only if part
> number is FUJITSU_CPU_PART_A64FX at this point. The details of the
> registers to be read and written in this patch are described below.
>
> "https://github.com/fujitsu/A64FX/tree/master/doc/"
>     A64FX_Specification_HPC_Extension_v1_EN.pdf
>
> Signed-off-by: Kohei Tarumizu <tarumizu.kohei@...itsu.com>
> ---
>  arch/arm64/kernel/pfctl.c | 368 ++++++++++++++++++++++++++++++++++++++

This has nothing to do with arm64 arch other than you access registers
as sysregs. That's not enough of a reason to put in arch/arm64. Move
this to drivers/ assuming it continues. I agree that this seems
questionable to expose to userspace in the first place...

Rob