[RFC 0/6] Deprecate riscv,isa DT property?

[Atish Patra]

On Thu, May 11, 2023 at 2:47 PM Conor Dooley <conor at kernel.org> wrote:
>
> On Thu, May 11, 2023 at 02:27:44PM -0700, Atish Patra wrote:
>
> > > The other thought I had was that perhaps some software may choose not to
> > > implement version x.y.0 of an extension and only support x.z.0, z > y
> > > for some reason. We'd want to refuse that extension if the extension is
> > > found, but the version is not listed as being something compatible with
> > > x.z.0, and while the ISA spec does say that the default assumption is
> > > 2p0 for unversioned extensions in its current form, I struggle to
> > > extrapolate that to extensions not currently part of the unpriv spec,
> > > but rather defined on their own.
> > >
> >
> > That's a fair point. However, any new RVI ISA extension will only have v1.0
> > as per my knowledge. Any new feature will have to be part of a
> > different extension.
> > At least that was the plan discussed last year.
>
> That's more than last year at this point, and nothing has changed in the
> documentation! Talk's cheap, ehh?
>

Yup. I will poke RVI folks to check if it still is the plan or changed !!

> > https://github.com/riscv/riscv-isa-manual/issues/781#issuecomment-983222655
> >
> > Are you aware of any discussion that changes this ?
>
> It's called "trust issues". I am far less worried about the addition of
> new features though than the removal of existing ones.
> Part of me fears for fence.i-less systems for example, but there would
> be other ways to bodge around the mess if it comes to pass.
> If we are *sure* that no extensions will modify features additively or
> subtractively, then this may not be needed at all & I can avoid having
> to bend dt-validate to my will.

Fair enough. Let's get some clarification first from RVI. It must be
documented in unpriv
spec. Otherwise, there is no point of promise :)

> We have no guarantees for vendor extensions on that front either,
> they're free to do what they like w.r.t. versioning, no?

Vendor extensions are wild west. Who knows what scheme they will use.
We will likely have a vendor specific string parsing logic. They can do whatever
in that to figure out the version if they require it.

-- 
Regards,
Atish