[Mesa-dev] [PATCH] i965: Fix ARB_indirect_parameters logic.

[Plamena Manolova]

This patch modifies the ARB_indirect_parameters logic in
brw_draw_prims, so that our implementation isn't affected if
another application attempts to use predicates. Previously we
were using a predicate with a DELTAS_EQUAL comparison operation
and relying on the MI_PREDICATE_DATA register being 0. Our code
to initialize MI_PREDICATE_DATA to 0 was incorrect, so we were
accidentally using whatever value was written there. Because the
kernel does not initialize the MI_PREDICATE_DATA register on
hardware context creation, we might inherit the value from whatever
context was last running on the GPU (likely another process).
The Haswell command parser also does not currently allow us to write
the MI_PREDICATE_DATA register. Rather than fixing this and requiring
an updated kernel, we switch to a different approach which uses a
SRCS_EQUAL predicate that makes no assumptions about the states of any
of the predicate registers.

Fixes: piglit.spec.arb_indirect_parameters.tf-count-arrays
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103085

Signed-off-by: Plamena Manolova <plamena.manolova at intel.com>
CC: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_draw.c | 45 +++++++++++-------------------------
 1 file changed, 14 insertions(+), 31 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_draw.c b/src/mesa/drivers/dri/i965/brw_draw.c
index 58145fad77..0259a75e1d 100644
--- a/src/mesa/drivers/dri/i965/brw_draw.c
+++ b/src/mesa/drivers/dri/i965/brw_draw.c
@@ -875,7 +875,6 @@ brw_draw_prims(struct gl_context *ctx,
    struct brw_context *brw = brw_context(ctx);
    const struct gl_vertex_array **arrays = ctx->Array._DrawArrays;
    int predicate_state = brw->predicate.state;
-   int combine_op = MI_PREDICATE_COMBINEOP_SET;
    struct brw_transform_feedback_object *xfb_obj =
       (struct brw_transform_feedback_object *) gl_xfb_obj;
 
@@ -919,49 +918,33 @@ brw_draw_prims(struct gl_context *ctx,
     * to it.
     */
 
-    if (brw->draw.draw_params_count_bo &&
-        predicate_state == BRW_PREDICATE_STATE_USE_BIT) {
-      /* We need to empty the MI_PREDICATE_DATA register since it might
-       * already be set.
-       */
-
-      BEGIN_BATCH(4);
-      OUT_BATCH(MI_PREDICATE_DATA);
-      OUT_BATCH(0u);
-      OUT_BATCH(MI_PREDICATE_DATA + 4);
-      OUT_BATCH(0u);
-      ADVANCE_BATCH();
-
-      /* We need to combine the results of both predicates.*/
-      combine_op = MI_PREDICATE_COMBINEOP_AND;
-   }
-
    for (i = 0; i < nr_prims; i++) {
       /* Implementation of ARB_indirect_parameters via predicates */
       if (brw->draw.draw_params_count_bo) {
-         struct brw_bo *draw_id_bo = NULL;
-         uint32_t draw_id_offset;
-
-         intel_upload_data(brw, &prims[i].draw_id, 4, 4, &draw_id_bo,
-                           &draw_id_offset);
-
          brw_emit_pipe_control_flush(brw, PIPE_CONTROL_FLUSH_ENABLE);
 
+         /* Upload the current draw count from the draw parameters buffer to MI_PREDICATE_SRC0.*/
          brw_load_register_mem(brw, MI_PREDICATE_SRC0,
                                brw->draw.draw_params_count_bo,
                                brw->draw.draw_params_count_offset);
-         brw_load_register_mem(brw, MI_PREDICATE_SRC1, draw_id_bo,
-                               draw_id_offset);
+         /* Zero the top 32-bits of MI_PREDICATE_SRC0 */
+         brw_load_register_imm32(brw, MI_PREDICATE_SRC0 + 4, 0);
+         /* Upload the id of the current primitive to MI_PREDICATE_SRC1.*/
+         brw_load_register_imm64(brw, MI_PREDICATE_SRC1, prims[i].draw_id);
 
          BEGIN_BATCH(1);
-         OUT_BATCH(GEN7_MI_PREDICATE |
-                   MI_PREDICATE_LOADOP_LOADINV | combine_op |
-                   MI_PREDICATE_COMPAREOP_DELTAS_EQUAL);
+         if (i == 0 && brw->predicate.state != BRW_PREDICATE_STATE_USE_BIT) {
+            OUT_BATCH(GEN7_MI_PREDICATE | MI_PREDICATE_LOADOP_LOADINV |
+                      MI_PREDICATE_COMBINEOP_SET |
+                      MI_PREDICATE_COMPAREOP_SRCS_EQUAL);
+         } else {
+            OUT_BATCH(GEN7_MI_PREDICATE |
+                      MI_PREDICATE_LOADOP_LOAD | MI_PREDICATE_COMBINEOP_XOR |
+                      MI_PREDICATE_COMPAREOP_SRCS_EQUAL);
+         }
          ADVANCE_BATCH();
 
          brw->predicate.state = BRW_PREDICATE_STATE_USE_BIT;
-
-         brw_bo_unreference(draw_id_bo);
       }
 
       brw_draw_single_prim(ctx, arrays, &prims[i], i, xfb_obj, stream,
-- 
2.11.0