Comment 51 for bug 1339939

(In reply to comment #45)
> (In reply to comment #44)
> > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > index 5a74986348c6..b46b3e928a7f 100644
> > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > @@ -530,6 +530,17 @@ static int init_ring_common(struct intel_ring_buffer
> > *ring)
> > ((ring->size - PAGE_SIZE) & RING_NR_PAGES)
> > | RING_VALID);
> >
> > + if (I915_READ_START(ring) != i915_gem_obj_ggtt_offset(obj)) {
> > + printk(KERN_ERR
> > + "%s initialization failed"
> > + " [%08x != %08x], fudging\n",
> > + ring->name,
> > + I915_READ_START(ring),
> > + i915_gem_obj_ggtt_offset(obj));
> > + I915_WRITE_START(ring, i915_gem_obj_ggtt_offset(obj));
> > + POSTING_READ(ring);
> > + }
> > +
> > iowrite32(MI_NOOP, ring->virtual_start + 0);
> > iowrite32(MI_NOOP, ring->virtual_start + 4);
> > ring->write_tail(ring, 8);
>
> What is a baseline I should apply this on top of, please? The surrounding
> code in my tree (with all the patches provided so far apples) is
>
> [ ... ]
> I915_WRITE_CTL(ring,
> ((ring->size - PAGE_SIZE) & RING_NR_PAGES)
> | RING_VALID);
> if (wait_for(I915_READ_CTL(ring) & RING_VALID, 1000)) {
> DRM_ERROR("%s initialization failed ctl %08x (valid? %d)\n",
> ring->name,
> I915_READ_CTL(ring),
> !!(I915_READ_CTL(ring) & RING_VALID));
> ret = -EIO;
> goto out;
> }
> I915_WRITE_HEAD(ring, 0);
> ring->write_tail(ring, 0);
>
> iowrite32(MI_NOOP, ring->virtual_start + 0);
> iowrite32(MI_NOOP, ring->virtual_start + 4);
> ring->write_tail(ring, 8);
> [ ... ]
>
> (i.e. it has the extra I915_WRITE_HEAD(ring, 0); ring->write_tail(ring, 0);,
> etc).
>
> I can of course easily apply the hunk just between the
>
> ring->write_tail(ring, 0);
>
> and
>
> iowrite32(MI_NOOP, ring->virtual_start + 0);
>
> if that's what you want me to do.
>
> Thanks.

Sorry, I threw away the preceding hack to try and keep the diff clean. Just plonk the write to set HEAD again after setting CTRL (and the wait_for(CTRL) if you have that).

Hmm, it appears we have drifted slightly in our assortment of patches, let me push my current collection of hacks so we can rebase.