[Intel-gfx] [PATCH 04/17] drm/i915: Wrap around the tail offset before setting ring->tail

[Chris Wilson]

Quoting Mika Kuoppala (2018-06-11 11:16:14)
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > index 409f499c0a45..7970ecb199e2 100644
> > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > @@ -496,6 +496,10 @@ static int init_ring_common(struct intel_engine_cs *engine)
> >               DRM_DEBUG_DRIVER("%s initialization failed [head=%08x], fudging\n",
> >                                engine->name, I915_READ_HEAD(engine));
> >  
> > +     /* Check that the ring offsets point within the ring! */
> > +     GEM_BUG_ON(!intel_ring_offset_valid(ring, ring->head));
> > +     GEM_BUG_ON(!intel_ring_offset_valid(ring, ring->tail));
> > +
> >       intel_ring_update_space(ring);
> >       I915_WRITE_HEAD(engine, ring->head);
> >       I915_WRITE_TAIL(engine, ring->tail);
> > @@ -1064,6 +1068,7 @@ int intel_ring_pin(struct intel_ring *ring,
> >  
> >  void intel_ring_reset(struct intel_ring *ring, u32 tail)
> >  {
> > +     tail = intel_ring_wrap(ring, tail);
> 
> I am pondering this wrap here and it's usefulness. Where
> could we ever get a tail which is not valid? From corrupted
> context?

It's just being defensive. We could make this
GEM_BUG_ON(!offset_valid()) instead?

Your choice?
-Chris