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

[Guo Ren]

On Thu, May 20, 2021 at 9:47 AM Guo Ren <guoren at kernel.org> wrote:
>
> On Wed, May 19, 2021 at 3:15 PM Anup Patel <anup at brainfault.org> wrote:
> >
> > On Wed, May 19, 2021 at 12:24 PM Drew Fustini <drew at beagleboard.org> wrote:
> > >
> > > 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.
> >
> > The current Linux RISC-V policy is to only accept patches for frozen or
> > ratified ISA specs.
> > (Refer, Documentation/riscv/patch-acceptance.rst)
> >
> > This means even if emulate CMO instructions in OpenSBI, the Linux
I think it's CBO now.
https://github.com/riscv/riscv-CMOs/blob/master/discussion-files/RISC_V_range_CMOs_bad_v1.00.pdf

> > patches won't be taken by Palmer because CMO specification is
> > still in draft stage.
> How do you think about
> sbi_ecall(SBI_EXT_DMA, SBI_DMA_SYNC, start, size, dir, 0, 0, 0);
> ? thx
CBO insn trap is okay for me ;-)

> >
> > Also, we all know how much time it takes for RISCV international
> > to freeze some spec. Judging by that we are looking at another
> > 3-4 years at minimum.
> >
> > Regards,
> > Anup
>
>
>
> --
> Best Regards
>  Guo Ren
>
> ML: https://lore.kernel.org/linux-csky/



-- 
Best Regards
 Guo Ren

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