[Intel-gfx] [PATCH 2/4] drm/i915: Force ringbuffers to not be at offset 0

[Chris Wilson]

On Sat, Apr 09, 2016 at 10:27:37AM +0100, Chris Wilson wrote:
> For reasons unknown Sandybridge GT1 (at least) will eventually hang when
> it encounters a ring wraparound at offset 0. The test case that
> reproduces the bug reliably forces a large number of interrupted context
> switches, thereby causing very frequent ring wraparounds, but there are
> similar bug reports in the wild with the same symptoms, seqno writes
> stop just before the wrap and the ringbuffer at address 0. It is also
> timing crucial, but adding various delays hasn't helped pinpoint where
> the window lies.

This also seems to fix resume on my SNB-GT2, but I guess that is a
different issue related to address 0. And long ago, I reported PNV also
hung when resumed when it hang ringbuffers at address 0 - so I wonder if
that's the same as well...
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre