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

[Christoph Hellwig]

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.