Re: [PATCH v8 0/7] Add non-coherent DMA support for AX45MP

[Palmer Dabbelt]

On Sun, 16 Apr 2023 23:53:17 PDT (-0700), Christoph Hellwig wrote:
> On Wed, Apr 12, 2023 at 09:32:30PM +0100, Conor Dooley wrote:
> > On Wed, Apr 12, 2023 at 12:08:53PM +0100, Prabhakar wrote:
> >
> > > Note,
> > > - This series requires testing on Cores with zicbom and T-Head SoCs
> >
> > As I said last time, I dunno what actual Zicbom stuff exists, other than
> > perhaps the Ventana lads having something. I did some tyre kicking on my
> > D1 and it was fine, although nothing has actually changed materially for
> > either of them with this series in v8..
>
> And as saying before, there is absolutely no reason to add non-standard
> non-coherent DMA support and let this cancer creep.  If you want Linux
> support implement Zicbom, be that in hardware or the SBI.

IMO we should just take the support in Linux: trying to hide stuff behind the
SBI leads to more more headaches than it's worth, we end up with a bunch of
broken firmware to try and work around.  We've already got a mess here because
of the D1 support, we might as well just live with it.

In practice there's just going to be a ton of mess in arch/riscv, as the ISA
has been missing many core features for many years and hardware vendors are
allowed to do whatever they want.  That's obviously a huge headache, but I
think there's nothing we can really do about it.