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

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Date:   Mon, 3 Apr 2023 22:29:24 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Prabhakar <prabhakar.csengg@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Heiko Stuebner <heiko@...ech.de>, Guo Ren <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, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.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 v7 1/6] riscv: mm: dma-noncoherent: Switch using function
 pointers for cache management

On Thu, Mar 30, 2023 at 09:42:12PM +0100, Prabhakar wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> 
> Currently, selecting which CMOs to use on a given platform is done using
> and ALTERNATIVE_X() macro. This was manageable when there were just two
> CMO implementations, but now that there are more and more platforms coming
> needing custom CMOs, the use of the ALTERNATIVE_X() macro is unmanageable.
> 
> To avoid such issues this patch switches to use of function pointers
> instead of ALTERNATIVE_X() macro for cache management (the only drawback
> being performance over the previous approach).
> 
> void (*clean_range)(unsigned long addr, unsigned long size);
> void (*inv_range)(unsigned long addr, unsigned long size);
> void (*flush_range)(unsigned long addr, unsigned long size);
> 

NAK.  Function pointers for somthing high performance as cache
maintainance is a complete no-go.