[RFC PATCH v5] RISC-V: Add support for the Zfa extension

[Palmer Dabbelt]

On Thu, 29 Jun 2023 08:10:40 PDT (-0700), christoph.muellner@vrull.eu wrote:
> On Thu, Jun 29, 2023 at 5:07 PM Jeff Law <jeffreyalaw@gmail.com> wrote:
>>
>>
>>
>> On 6/29/23 01:52, Christoph Müllner wrote:
>> > The RISC-V Zfa extension has been frozen.
>> >
>> > As this was discussed elsewhere yesterday:
>> > * Should this patch wait for ratification?
>> > * Is this blocked by https://github.com/riscv-non-isa/riscv-asm-manual/pull/85 ?
>> >
>> > Nelson stated on Apr 12 (response to v4):
>> > "If there are no new instructions or encodings/formats changed in the
>> > future spec, then you should commit the patch when the extension is
>> > ratified."
>> >
>> > So my understanding is that this needs to wait for ratification and is
>> > not blocked by the mentioned PR.
>> Is there something special about Zfa that makes it desirable to wait for
>> ratification as opposed to standard practice of gating things as the
>> specs get to a Frozen state?
>
> Not to my knowledge.

Waiting for ratification is probably a bad idea, there's really no way 
to schedule around it.  That's a big part of the reason we've just 
waited for frozen.

IIUC we're just waiting on the assembler syntax to be accepted, it's not 
an ISA problem right now.

That said, we haven't historically even waited for RVI to define 
assembly syntax.  I think folks were hoping that some of the new RVI 
process would make sure all these other things get done as part of the 
standardization process, but in practice it's just ended up being a bit 
of red tape that results in no meaningful work getting done.

It's not all that hard to just add more flavors of assembler syntax 
later, so maybe we just merge this and stop bothering to wait for all 
these other non-ISA specs to resolve?

> BR
> Christoph