Re: [PATCH RFC 0/3] riscv: Add DMA_COHERENT support

[Guo Ren]

On Wed, May 19, 2021 at 1:20 PM Christoph Hellwig <hch@xxxxxx> wrote:
>
> On Wed, May 19, 2021 at 05:04:13AM +0000, guoren@xxxxxxxxxx wrote:
> > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> >
> > 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.
This is the lightest solution I could imagine, it avoids conflicts
with RISC-V ISA.

Since the existing RISC-V ISA cannot solve this problem, it is better
to provide some configuration for the SOC vendor to customize.

--
Best Regards
 Guo Ren

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