linux-kernel - Re: [PATCH RFC 0/3] riscv: Add DMA

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Date:   Tue, 18 May 2021 23:54:31 -0700
From:   Drew Fustini <drew@...gleboard.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Guo Ren <guoren@...nel.org>, Anup Patel <anup.patel@....com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>, wefu@...hat.com,
        lazyparser@...il.com,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-sunxi@...ts.linux.dev, Guo Ren <guoren@...ux.alibaba.com>,
        paul.walmsley@...ive.com
Subject: Re: [PATCH RFC 0/3] riscv: Add DMA_COHERENT support

On Wed, May 19, 2021 at 08:06:17AM +0200, Christoph Hellwig wrote:
> On Wed, May 19, 2021 at 02:05:00PM +0800, Guo Ren wrote:
> > Since the existing RISC-V ISA cannot solve this problem, it is better
> > to provide some configuration for the SOC vendor to customize.
> 
> We've been talking about this problem for close to five years.  So no,
> if you don't manage to get the feature into the ISA it can't be
> supported.

Isn't it a good goal for Linux to support the capabilities present in
the SoC that a currently being fab'd?

I believe the CMO group only started last year [1] so the RV64GC SoCs
that are going into mass production this year would not have had the
opporuntiy of utilizing any RISC-V ISA extension for handling cache
management.

Thanks,
Drew

[1] https://github.com/riscv/riscv-CMOs