linux-kernel - Re: [PATCH v9 3/6] riscv: mm: dma-noncoherent: nonstandard cache operations support

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Message-ID: <CA+V-a8utPvBdwR78NVxpnuUWgniVvopnK4PvmWGEfkfSv5AQHQ@mail.gmail.com>
Date:   Fri, 16 Jun 2023 13:13:44 +0100
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "Conor.Dooley" <conor.dooley@...rochip.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        guoren <guoren@...nel.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Samuel Holland <samuel@...lland.org>,
        linux-riscv@...ts.infradead.org,
        Christoph Hellwig <hch@...radead.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>,
        "Lad, Prabhakar" <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v9 3/6] riscv: mm: dma-noncoherent: nonstandard cache
 operations support

Hi Arnd,

Thank you for the review.

On Wed, Jun 14, 2023 at 1:36 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Wed, Jun 14, 2023, at 12:47, Prabhakar wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Introduce support for nonstandard noncoherent systems in the RISC-V
> > architecture. It enables function pointer support to handle cache
> > management in such systems.
> >
> > This patch adds a new configuration option called
> > "RISCV_NONSTANDARD_CACHE_OPS." This option is a boolean flag that
> > depends on "RISCV_DMA_NONCOHERENT" and enables the function pointer
> > support for cache management in nonstandard noncoherent systems.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
>
> I understand that Christoph will still not like this, but I think this
> is as good as it gets, making the standard variant the fast path,
> and using the function pointers only for the nonstandard cases.
>
>
> >  #include <asm/cacheflush.h>
> > +#include <asm/dma-noncoherent.h>
> >
> >  static bool noncoherent_supported;
> >
> > +struct riscv_cache_ops noncoherent_cache_ops = {
> > +     .clean = NULL,
> > +     .inval = NULL,
> > +     .flush = NULL,
> > +};
>
> This could be marked __read_mostly or __ro_after_init as
> a micro-optimization, if anyone cares.
>
Ok, I will do that in the next version.

Cheers,
Prabhakar