[Piglit] [PATCH] glsl-1.50-geometry-primitive-id-restart: Add workaround for Intel SandyBrige

[Samuel Iglesias Gonsalvez]

Intel SandyBridge is not handling GL_TRIANGLE_STRIP_ADJACENCY with
repeating vertex indices correctly, so there is a GPU hang when
running:

bin/glsl-1.50-geometry-primitive-id-restart \
GL_TRIANGLE_STRIP_ADJACENCY ffs

This patch provides a workaround for this issue as it seems to be a HW
bug in SandyBrigde. More information:

http://lists.freedesktop.org/archives/mesa-dev/2014-July/064221.html

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias at igalia.com>
---

If there is no objections, we plan to push this patch next week because
it is needed to avoid GPU hangs when testing GS support patches for SNB.

Before pushing it, we will send a reminder to the mailing list, just in
case.

 .../execution/geometry/primitive-id-restart.c         | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/tests/spec/glsl-1.50/execution/geometry/primitive-id-restart.c b/tests/spec/glsl-1.50/execution/geometry/primitive-id-restart.c
index 9f1a8ef..1e748c3 100644
--- a/tests/spec/glsl-1.50/execution/geometry/primitive-id-restart.c
+++ b/tests/spec/glsl-1.50/execution/geometry/primitive-id-restart.c
@@ -218,11 +218,22 @@ piglit_init(int argc, char **argv)
 	num_elements = 0;
 	for (i = 1; i <= LONGEST_INPUT_SEQUENCE; i++) {
 		for (j = 0; j < i; j++) {
-			/* Every element that isn't the primitive
-			 * restart index can just be element 0, since
-			 * we don't care about the actual vertex data.
+			/* Every element that isn't the primitive restart index
+			 * can have any value as far as it is not the primitive
+			 * restart index since we don't care about the actual
+			 * vertex data.
+			 *
+			 * NOTE: repeating the indices for all elements but the
+			 * primitive restart index causes a GPU hang in Intel's
+			 * Sandy Bridge platform, likely due to a hardware bug,
+			 * so make sure that we do not repeat the indices.
+			 *
+			 * More information:
+			 *
+			 * http://lists.freedesktop.org/archives/mesa-dev/2014-July/064221.html
 			 */
-			elements[num_elements++] = 0;
+			elements[num_elements++] =
+				j != prim_restart_index ? j : j + 1;
 		}
 		elements[num_elements++] = prim_restart_index;
 	}
-- 
2.1.0