linux-kernel - Re: [PATCH v7 1/6] riscv: mm: dma-noncoherent: Switch using function pointers for cache management

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Date:   Fri, 7 Apr 2023 02:03:36 +0200
From:   Andrea Parri <parri.andrea@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Biju Das <biju.das.jz@...renesas.com>,
        Prabhakar <prabhakar.csengg@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Arnd Bergmann <arnd@...db.de>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Samuel Holland <samuel@...lland.org>,
        Heiko Stuebner <heiko@...ech.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Rob Herring <robh+dt@...nel.org>, Guo Ren <guoren@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        Andrew Jones <ajones@...tanamicro.com>
Subject: Re: [PATCH v7 1/6] riscv: mm: dma-noncoherent: Switch using function
 pointers for cache management

> But other other point is adding more cache flushing variants should not
> be easy.  Everyone should be using the standardize version.  If it's not
> implemented in hardware despite having ratified extensions you can fake
> it up in SBI.  Yes, that's way more expensive than indirect calls, but
> that's what you get for taping out new hardware that ignores the actual
> architecture specification and just does their own made up shit.

FWIW, ALTERNATIVE_X() for "three instructions with (what should be a)
crystal-clear semantics" already smells like "we're doing it wrong" to
me, function pointers would be closer to "we're looking for trouble".

Thanks,
  Andrea