linux-kernel - Re: [RFC PATCH v1 04/10] RISC-V: Use IPIs for remote TLB flush when possible

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Date:   Sun, 13 Jun 2021 10:33:06 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Anup Patel <anup.patel@....com>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Atish Patra <atish.patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [RFC PATCH v1 04/10] RISC-V: Use IPIs for remote TLB flush when possible

On Sat, 12 Jun 2021 17:04:16 +0100,
Anup Patel <anup.patel@....com> wrote:
> 
> If IPI calls are injected using SBI IPI calls then remote TLB flush
> using SBI RFENCE calls is much faster because using IPIs for remote
> TLB flush would still endup as SBI IPI calls with extra processing
> on kernel side.
> 
> It is now possible to have specialized hardware (such as RISC-V AIA)
> which allows S-mode software to directly inject IPIs without any
> assistance from M-mode runtime firmware.
> 
> This patch extends remote TLB flush functions to use IPIs whenever
> underlying IPI operations are suitable for remote FENCEs.
> 
> Signed-off-by: Anup Patel <anup.patel@....com>
> ---
>  arch/riscv/mm/tlbflush.c | 62 +++++++++++++++++++++++++++++++---------
>  1 file changed, 48 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> index 720b443c4528..009c56fa102d 100644
> --- a/arch/riscv/mm/tlbflush.c
> +++ b/arch/riscv/mm/tlbflush.c
> @@ -1,39 +1,73 @@
>  // SPDX-License-Identifier: GPL-2.0
> +/*
> + * TLB flush implementation.
> + *
> + * Copyright (c) 2021 Western Digital Corporation or its affiliates.
> + */

I find this a bit odd. You don't mention this addition in the commit
message, and a quick look at the commits touching tlbflush.[ch]
doesn't make the copyright assignment obvious (most commits originate
from either SiFive or Christoph).

In any way, please keep this kind of changes out of this series if
possible, and have a separate discussion on who gets to brag about
this code.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.