Status of the various RISC-V specification and policy

[Palmer Dabbelt]

On Thu, 30 Sep 2021 10:38:02 PDT (-0700), markhimelstein at riscv.org wrote:
> The following is the extension lifecycle. It includes the official names
> going forward for each phase. We are trying to resolve any confusion naming
> and numbering and are still in progress of this evolution:
>
> https://docs.google.com/presentation/d/1nQ5uFb39KA6gvUi5SReWfIQSiRN7hp6z7ZPfctE4mKk/edit?usp=sharing
>
> Again, if we can improve anything to make it clearer or if we got something
> wrong, please let us know.

That is, unfortunately, even more confusing.

Slide 3 lists the milestones, but that uses very different terms than 
the "Specification States" wiki entry I was linked to earlier as the 
canonical definition of the process.  I'm also now less sure about what 
exactly is being frozen, as the slides seem to mix up extension and 
specification (which is the core of what I'm worried about).

Looking at slide 4 (titled "Extension Lifecycle"), I see a bunch of 
version number looking strings (things like "v0.1" and "v1.0-rcN 
(final)").  Are those versions, and if so what do they version?

It also says "v1.0 (ratified)" with an arrow pointing directly after 
"TSC Ratification Review & Vote", but in the v-1.0 tag I see "Once ratified, 
the spec will be given version 2.0."  Are these version-number-looking 
strings supposed to be things that exist within the same namespace?

Just loking over the slide again I see "New or Changed Features 
Specification Development become a new extension -- Go back to the top 
left".  That sort of seems like something that might help answer some of 
my core questionsn here around what's allowed to change when, but I'm 
genuinely not sure how to parse the words.  Might not be the most 
important thing to focus on now, though.

>
> Mark
>
> On Thu, Sep 30, 2021 at 10:30 AM Palmer Dabbelt <palmer at dabbelt.com> wrote:
>
>> On Thu, 30 Sep 2021 08:06:42 PDT (-0700), markhimelstein at riscv.org wrote:
>> > Palmer,
>> >
>> >
>> >
>> > Thank you for your input.
>> >
>> >
>> >
>> > Our strong intention is to not change specs once frozen. I speak for the
>> > committees here and say that, in our opinion, declaring something frozen
>> > sets a very high bar for making any changes and is sufficient to allow
>> code
>> > supporting an extension to be upstreamed. Of course if an unexpected and
>> > significant issue is discovered during the public review that absolutely
>> > must be addressed and cannot be deferred to a future extension (where the
>> > cost of not addressing the issue exceeds the cost of addressing it. for
>> > example introduces security vulnerabilities), then we will do so, as
>> anyone
>> > should expect from a public review.
>> >
>> >
>> >
>> > We do not have versions of extensions. If an extension has a problem once
>> > ratified, we will issue errata. All implementers have to publish the
>> errata
>> > if they use branding. We may release a new extension with the bulk of the
>> > original extension plus the errata fix at some future date.
>>
>> This is probably at the core of my confusion here.
>>
>> At the preface of the user ISA there is a table with the headings
>> "Extension", "Version", and "Frozen"; contains a list of letters that
>> look like extension name; and contains a list of numbers that look like
>> versions of those extensions.
>>
>> That nomenclature seems to carry on to some more recent specifications.
>> For example the first page of
>>
>> https://github.com/riscv/riscv-v-spec/releases/download/v1.0/riscv-v-spec-1.0.pdf
>> (tagged 11 days ago) is
>>
>>     RISC-V "V" Vector Extension
>>     Version 1.0
>>
>> I'm happy to answer the rest of the questions here, but I think trying
>> to get on the same page about what is versioned and is proabbly the
>> first step because that's a pretty key component of my worries.
>>
>> > New extensions reserve the right to be incompatible with existing
>> > extensions but our philosophy is very much to minimize that and only
>> allow
>> > the rare well-justified exceptions.  Reasons may include errata, security
>> > issues discovered, or new functionality we need to add that justifies
>> > creating an incompatibility, etc.
>> >
>> > What specifically do you see as an issue? What are you blocked on by our
>> > conventions? We need specific details to resolve any issues. Right now, I
>> > don't feel I have enough information from you.
>> >
>> >
>> >
>> > Thanks
>> >
>> > Mark
>> >
>> >
>> >
>> > P.S. We had some situations in the past, in part due to vendors not
>> waiting
>> > for the specification processes to conclude, where implementers
>> implemented
>> > non-confoming chips either with vendor-specific extensions using reserved
>> > opcodes and state, or implementing early drafts of standards-track
>> > proposals in the development state (will likely change). This is in the
>> > past and resolved. Anyone implementing non-standard extensions must
>> > advertise them as such and make it clear that these are not standard
>> RISC-V
>> > extensions: this should make it clear for upstream projects that they
>> will
>> > be dealing with the respective vendors for support and maintenance, and
>> > that any code implementing support for these extensions will be different
>> > from what covers the respective standard extensions. Whether upstream
>> > projects accept such changes, and what conditions they stipulate for
>> > acceptance of these changes, are beyond the control of RISC-V.  We also,
>> as
>> > I have described to you many times, have instituted mandatory standards
>> > specification states for the front page of each specification to ensure
>> > clarity (any divergence from this is a bug and we work to fix these
>> > quickly).
>> >
>> >
>> > On Tue, Sep 28, 2021 at 11:34 AM Palmer Dabbelt <palmer at dabbelt.com>
>> wrote:
>> >
>> >> On Mon, 27 Sep 2021 08:57:15 PDT (-0700), markhimelstein at riscv.org
>> wrote:
>> >> > the words in this document :
>> >> >
>> >> >
>> >>
>> https://wiki.riscv.org/plugins/servlet/mobile?contentId=13098230#content/view/13098230
>> >> >
>> >> > make it very clear when changes are allowed or not and likely or not.
>> >> >
>> >> > if you think the verbiage is somehow ambiguous please help us make it
>> >> better.
>> >>
>> >> I'm not really worried about changes, I'm worried about a committment to
>> >> future compatibility.  When we take code into the kernel (and most other
>> >> core systems projects) we're taking on the burden of supporting (until
>> >> someone can prove there are no more users), which is very difficult to
>> >> do when the ISA changes in an incompatible fashion.  The whole point of
>> >> agreeing on the frozen thing was that it gave us a committment from the
>> >> specifcation authors that the future ISA would be compatible with th
>> >> frozen extensions.
>> >>
>> >> We're already in this spot with the V extension and the whole stable
>> >> thing, this definitaion of frozen looks very much like what was has led
>> >> to the issues there.  Saying the spec won't change really isn't
>> >> meaningful, it's saying future specs will be compatible that's
>> >> important.  Nothing in this whole rule touches on compatibility, and I
>> >> really don't want to end up in a bigger mess than we're already in.
>> >>
>> >> (Also: some PGE subcontractor drove a crane into my house, so things are
>> >> a bit chaotic on my end.  If you have that list of what's officially
>> >> frozen, can you send it out?  I'll try to take a look ASAP, as then I
>> >> can at least focus the discussion on what's relevant right now.)
>> >>
>> >> >
>> >> > Mark
>> >> > --------
>> >> > sent from a mobile device. please forgive any typos.
>> >> >
>> >> >> On Sep 27, 2021, at 8:50 AM, Palmer Dabbelt <palmer at dabbelt.com>
>> wrote:
>> >> >>
>> >> >> On Tue, 21 Sep 2021 17:20:17 PDT (-0700), atishp at atishpatra.org
>> wrote:
>> >> >>> Hi All,
>> >> >>> Please find the below email from Stephano about the freeze
>> >> announcement for
>> >> >>> various RISC-V specifications that will be part of privilege
>> >> specification
>> >> >>> v1.12.
>> >> >>> All the review discussions are happening in the isa-dev mailing
>> list.
>> >> The
>> >> >>> review period will be open for 45 days ending Sunday October 31,
>> 2021.
>> >> >>>
>> >> >>> I just want to highlight the fact that the *H*, *V, SvPBMT, CMO
>> >> extensions
>> >> >>> are frozen now. *This will help us merge some patches that have been
>> >> >>> present in the mailing list for a while.
>> >> >>>
>> >> >>> Here are the ratification policy and extension life cycle documents
>> >> present
>> >> >>> in the public. If you have any questions regarding this, please
>> check
>> >> with
>> >> >>> Mark/Stephano (cc'd).
>> >> >>>
>> >> >>> Ratification policy:
>> >> >>>
>> >>
>> https://docs.google.com/document/d/1-UlaSGqk59_myeuPMrV9gyuaIgnmFzGh5Gfy_tpViwM/edit
>> >> >>>
>> >> >>> Extension life cycle:
>> >> >>>
>> >>
>> https://docs.google.com/presentation/d/1nQ5uFb39KA6gvUi5SReWfIQSiRN7hp6z7ZPfctE4mKk/edit#slide=id.p1
>> >> >>
>> >> >> I'm still buried after Plumbers, but one of the bits on my TODO list
>> >> was to look throught the new definitions for frozen and stable.
>> Nothing in
>> >> this extension life cycle talks about the point at which compatibility
>> will
>> >> be maintained, which was really the central point behind frozen before.
>> >> >>
>> >> >> Are there more concrete definitions somewhere?
>> >>
>>