linux-kernel - Re: [PATCH v4 5/7] riscv: mm: dma-noncoherent: Pass direction and operation to ALT_CMO

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Message-ID: <CA+V-a8tZgswanaN2gbmWzswO4pLLQ884aQa+KVNLwjDS9YqS=A@mail.gmail.com>
Date:   Fri, 25 Nov 2022 20:53:02 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Heiko Stübner <heiko@...ech.de>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Guo Ren <guoren@...nel.org>,
        Jisheng Zhang <jszhang@...nel.org>,
        Atish Patra <atishp@...osinc.com>,
        Anup Patel <apatel@...tanamicro.com>,
        Andrew Jones <ajones@...tanamicro.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-renesas-soc@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v4 5/7] riscv: mm: dma-noncoherent: Pass direction and
 operation to ALT_CMO_OP()

Hi Samuel,

Thank you for the review.

On Fri, Nov 25, 2022 at 6:49 PM Samuel Holland <samuel@...lland.org> wrote:
>
> On 11/24/22 13:18, Lad, Prabhakar wrote:
> > Hi Heiko,
> >
> > Thank you for the review.
> >
> > On Thu, Nov 24, 2022 at 6:29 PM Heiko Stübner <heiko@...ech.de> wrote:
> >>
> >> Am Donnerstag, 24. November 2022, 18:22:05 CET schrieb Prabhakar:
> >>> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >>>
> >>> Pass direction and operation to ALT_CMO_OP() macro.
> >>>
> >>> This is in preparation for adding errata for the Andes CPU core.
> >>
> >> can you provide more explanation why that is necessary please?
> >> I guess you want to use different cache operations for some cases?
> >>
> > Yes basically to call different cache operations based on the dir and
> > operations (and also this allows to export just one function to handle
> > the errata). I'll update the commit message in the next version.
>
> This makes things less efficient, because it requires more instructions
> and registers inside the alternative section, and your function
> duplicates the logic from arch_sync_dma_for_device(). The alternative is
> already passed the operation (clean/flush/invalidate) as a token, so you
> can construct the function name with token pasting.
>
I did think about it but that didn't help for example in the
arch_dma_prep_coherent() we are calling flush token, but on RZ/Five
for arch_dma_prep_coherent() we have to do nothing.

Cheers,
Prabhakar