Re: [Qemu-devel] RISC-V: Vector && DSP Extension

[Peter Maydell]

On Thu, 15 Aug 2019 at 09:53, Aleksandar Markovic
<address@hidden> wrote:
>
> > We can accept draft
> > extensions in QEMU as long as they are disabled by default.

> Hi, Alistair, Palmer,
>
> Is this an official stance of QEMU community, or perhaps Alistair's
> personal judgement, or maybe a rule within risv subcomunity?

Alistair asked on a previous thread; my view was:
https://lists.gnu.org/archive/html/qemu-devel/2019-07/msg03364.html
and nobody else spoke up disagreeing (summary: should at least be
disabled-by-default and only enabled by setting an explicit
property whose name should start with the 'x-' prefix).

In general QEMU does sometimes introduce experimental extensions
(we've had them in the block layer, for example) and so the 'x-'
property to enable them is a reasonably established convention.
I think it's a reasonable compromise to allow this sort of work
to start and not have to live out-of-tree for a long time, without
confusing users or getting into a situation where some QEMU
versions behave differently or to obsolete drafts of a spec
without it being clear from the command line that experimental
extensions are being enabled.

There is also an element of "submaintainer judgement" to be applied
here -- upstream is probably not the place for a draft extension
to be implemented if it is:
 * still fast moving or subject to major changes of design direction
 * major changes to the codebase (especially if it requires
   changes to core code) that might later need to be redone
   entirely differently
 * still experimental

thanks
-- PMM