[Bug 84104] Ring hang with geometry shaders on SNB

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=84104

--- Comment #1 from Kenneth Graunke <kenneth at whitecape.org> ---
Our use of "Dual OWord Block" messages appears to be confusing the simulator;
the second offset is not set to a proper value, so it usually ends up being
out-of-range and tripping assertions.  We may want to use a different kind of
message.

But, that doesn't appear to be the real problem.  Tentatively, it looks like
the clipper is hitting an assertion about an unknown primitive topology exiting
the GS.

On Gen6, it appears that we have to set the output topology in the GS URB Write
message header.  I am not convinced that we're doing that correctly in all
cases.  I noticed we zero out the input topology field in g0 right away - which
should be fine, because we have the output topology as
prog_data->output_topology.  We attempt to set that properly, but I'm not sure
if we set it on every vertex - it looks like we may only set it on the first
one.  Perhaps someone can sanity check this.

That said, I'm also seeing utterly bizarre values for topology in the simulator
dump output - in the "primitive-id-restart GL_TRIANGLE_STRIP_ADJACENCY" test,
it sure looks like we're getting 3DPRIM_QUADSTRIP going from the VS->GS, and
again going from GS->CL (which is unsupported, and will trigger an assert).

Maybe my analysis is wrong; I can't imagine how that could be.

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