[Intel-gfx] [PATCH 3/7] drm/i915: Signal fence completion from i915_request_wait

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-06-19 15:27:21)
> 
> On 19/06/2019 12:23, Chris Wilson wrote:
> > With the upcoming change to automanaged i915_active, the intent is that
> > whenever we wait on the set of active fences, they are signaled and
> > collected.  The requirement is that all successful returns from
> > i915_request_wait() signal the fence, so fixup the one remaining path
> > where we may return before the interrupt has been run.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > ---
> >   drivers/gpu/drm/i915/i915_request.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> > index 0c2b53b8a3d1..8d59c35bd22f 100644
> > --- a/drivers/gpu/drm/i915/i915_request.c
> > +++ b/drivers/gpu/drm/i915/i915_request.c
> > @@ -1451,8 +1451,10 @@ long i915_request_wait(struct i915_request *rq,
> >       for (;;) {
> >               set_current_state(state);
> >   
> > -             if (i915_request_completed(rq))
> > +             if (i915_request_completed(rq)) {
> > +                     dma_fence_signal(&rq->fence);
> >                       break;
> > +             }
> >   
> >               if (signal_pending_state(state, current)) {
> >                       timeout = -ERESTARTSYS;
> > 
> 
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Patch is fine, but I have to say commit message scares me a bit. Where 
> are we adding such subtle fragility that wait has to exit with fence 
> signaled? Is it just some specific i915_request_wait call site or all of 
> them?

dma_fence_wait_default already implies that the fence is signaled prior
to its return, so in terms of the bigger picture I can argue this bring
us into line.

In the scenarios I've been fixing it's basically making sure that
i915_gem_wait_for_idle() does guarantee that we idle, which involves
some assurance that the request are retired, and uses
i915_request_wait() directly for the most part.
-Chris