[Intel-gfx] [PATCH] drm: avoid spurious EBUSY due to nonblocking atomic modesets

[Daniel Vetter]

On Tue, Sep 22, 2020 at 4:14 PM Daniel Stone <daniel at fooishbar.org> wrote:
>
> On Tue, 22 Sep 2020 at 15:04, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> > On Tue, Sep 22, 2020 at 3:36 PM Marius Vlad <marius.vlad at collabora.com> wrote:
> > > Gentle ping. I've tried out Linus's master tree and, and like Pekka,
> > > I've noticed this isn't integrated/added.
> >
> > Defacto the uapi we have now is that userspace needs to ignore "spurious" EBUSY.
>
> This really, really, really, bites.
>
> I think we need a guarantee that this never happens if ALLOW_MODESET
> is always used in blocking mode, plus in future a cap we can use to
> detect that we won't be getting spurious EBUSY events.
>
> I really don't want to ever paper over this, because it's one of the
> clearest indications that userspace has its timing/signalling wrong.

Ok so the hang-up last time around iirc was that I broke igt by making
a few things more synchronous. Let's hope I'm not also breaking stuff
with the WARN_ON ...

New plan:
- make this patch here only document existing behaviour and enforce it
with the WARN_ON
- new uapi would be behind a flag or something, with userspace and
everything hanging off it.

Thoughts?

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch