Re: [PATCH v8 00/78] support vector extension v1.0

[Alistair Francis]

On Mon, Oct 18, 2021 at 7:37 PM LIU Zhiwei <zhiwei_liu@c-sky.com> wrote:
>
> Hi Alistair,
>
> Sorry for the  send error.  And I have a question about this patch set.

Hello Zhiwei,

>
> Firstly, I totally support the vector v1.0 upstream.

Great!

>
> The concern is how to deal with the v0.7.1 code on QEMU. There are some
> products based on the vector v0.7.1,
> such as D1 SOC from Allwinner and  Xuantie CPU  from Alibaba. The Linux
> and GCC upstream for D1 is working in progress,
> and eventually these projects will support v0.7.1 in some way, probably
> as "x-thead-v" (the "thead" stands for Alibaba T-Head).

Yep, so QEMU's stance is to only support the latest version of a draft
specification. Once a specification moves from draft to frozen we will
also only support the frozen spec.

I understand that there is hardware with the v0.7.1 of the vector
extension. But in QEMU we don't have the resources for RISC-V to
maintain multiple sets of draft extensions. Especially the vector
extension, which is very different between v0.7.1 and v1.0 (see the 78
patches in this series).

I realise this is disappointing for companies and people who have
invested in v0.7.1 in QEMU, and I hope it doesn't put anyone off
upstream work. Having the v0.7.1 even for a short period of time has
been helpful for the vector extension development and related
software/tools.

>
> Maybe we can
>
> 1. Drop the v0.7.1 support permanently.
>
> 2. Drop the v0.7.1  temporarily and add  it  back later.

If in the future there is broad community support for v0.7.1 and we
can get some more QEMU resources for RISC-V we can re-evaluate v0.7.1
support. But for the time being it will just be dropped.

There are a few QEMU releases with v0.7.1 support, so you can use
those for development. The v0.7.1 has received a few bug fixes in the
upstream code base which will be beneficial for those using it.

Sorry about that

Alistair

>
> 3. Do some compatible work for v0.7.1 in the v1.0 patch set.
>
> Look forward to your idea. Thanks very much.
>
> Best Regards,
> Zhiwei
>
> On 2021/10/18 下午5:01, LIU Zhiwei wrote:
> > Hi Alistair,
> >
> > There is some products based on the vector v0.7.1, such as D1 SOC from
> > Allwinner and  Xuantie CPU  And we have spent a lot of work to
> > support  vector  on QEMU.
> >
> >
> >
> > Allwinner
> >
> >