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

[Daniel Stone]

Hi,

On Tue, 22 Sep 2020 at 17:02, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> On Tue, Sep 22, 2020 at 4:14 PM Daniel Stone <daniel at fooishbar.org> wrote:
> > 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?

What do you mean by 'new uapi'? The proposal that the kernel
communicates back which object IDs have been added to the state behind
your back? That it's been made automatically blocking? Something else?

Cheers,
Daniel (the other one)