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

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Message-ID: <CAJF2gTTjwB4U-NxCtfgMA5aR2HzoQtA8a51W5UM1LHGRbjz9pg@mail.gmail.com>
Date:   Wed, 19 May 2021 13:48:23 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Anup Patel <anup.patel@....com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        drew@...gleboard.org, 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>
Subject: Re: [PATCH RFC 0/3] riscv: Add DMA_COHERENT support

On Wed, May 19, 2021 at 1:20 PM Christoph Hellwig <hch@....de> wrote:
>
> On Wed, May 19, 2021 at 05:04:13AM +0000, guoren@...nel.org wrote:
> > From: Guo Ren <guoren@...ux.alibaba.com>
> >
> > The RISC-V ISA doesn't yet specify how to query or modify PMAs, so let
> > vendors define the custom properties of memory regions in PTE.
>
> Err, hell no.   The ISA needs to gets this fixed first.  Then we can
> talk about alternatives patching things in or trapping in the SBI.
> But if the RISC-V ISA can't get these basic done after years we can't
> support it in Linux at all.

The patchset just leaves a configuration chance for vendors. Before
RISC-V ISA fixes it, we should give the chance to let vendor solve
their real chip issues.

-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/