[PATCH] drm/syncobj: Allow wait for submit and signal behavior (v2)

[Jason Ekstrand]

On Wed, Aug 9, 2017 at 2:31 PM, Chris Wilson <chris at chris-wilson.co.uk>
wrote:

> Quoting Jason Ekstrand (2017-08-09 18:00:54)
> > +static signed long drm_syncobj_array_wait_timeout(struct drm_syncobj
> **syncobjs,
> > +                                                 uint32_t count,
> > +                                                 uint32_t flags,
> > +                                                 signed long timeout,
> > +                                                 uint32_t *idx)
> > +{
> > +       struct syncobj_wait_entry *entries;
> > +       struct dma_fence *fence;
> > +       signed long ret;
> > +       uint32_t signaled_count, i;
> > +
> > +       if (timeout == 0) {
> > +               signaled_count = 0;
> > +               for (i = 0; i < count; ++i) {
> > +                       ret = drm_syncobj_signaled(syncobjs[i], flags);
> > +                       if (ret < 0)
> > +                               return ret;
> > +                       if (ret == 0)
> > +                               continue;
> > +                       if (signaled_count == 0 && idx)
> > +                               *idx = i;
> > +                       signaled_count++;
> > +               }
> > +
> > +               if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_ALL)
> > +                       return signaled_count == count ? 1 : 0;
> > +               else
> > +                       return signaled_count > 0 ? 1 : 0;
>
> There's a very annoying laxness in the dma_fence API here, in that
> backends are not required to automatically report when a fence is
> signaled prior to fence->ops->enable_signaling() being called.
> So here if we fail to match signaled_count, we need to fallthough and
> try a 0 timeout wait!
>

That is very annoying!  I'll see how bad the fall-through is...


> Christian, dma_fence_wait_any_timeout() has this same bug you told me off
> for, e.g. commit 698c0f7ff216 ("dma-buf/fence: revert "don't wait when
> specified timeout is zero" (v2)")!
> -Chris
>
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