[Mesa-dev] [PATCH] i965: Emit Ivybridge VS workaround flushes.

[Kenneth Graunke]

I recently discovered this text in the BSpec.  It seems wise to comply,
though I haven't observed it to fix anything yet.

Fixes a regression in glean/fbo since 28cfa1fa213fe.

NOTE: This is a candidate for stable release branches.

Cc: Eric Anholt <eric at anholt.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45221
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/gen7_urb.c           |    2 +
 src/mesa/drivers/dri/i965/gen7_vs_state.c      |    2 +
 src/mesa/drivers/dri/intel/intel_batchbuffer.c |   26 ++++++++++++++++++++++-
 src/mesa/drivers/dri/intel/intel_batchbuffer.h |    1 +
 4 files changed, 29 insertions(+), 2 deletions(-)

This also obsoletes Eric's uncommitted patch
i965/gen7: Always allocate push constant space before uploading.
as it fixes the same problem without such a large performance hit.

My theory is that since 3DSTATE_PUSH_CONSTANT_ALLOC_VS is a non-pipelined
command, emitting it at the top of upload_vs_state effectively served the
same purpose (only a much harsher flush).

diff --git a/src/mesa/drivers/dri/i965/gen7_urb.c b/src/mesa/drivers/dri/i965/gen7_urb.c
index e6cf1eb..920c9fc 100644
--- a/src/mesa/drivers/dri/i965/gen7_urb.c
+++ b/src/mesa/drivers/dri/i965/gen7_urb.c
@@ -99,6 +99,8 @@ gen7_upload_urb(struct brw_context *brw)
    /* GS requirement */
    assert(!brw->gs.prog_active);
 
+   gen7_emit_vs_workaround_flush(intel);
+
    BEGIN_BATCH(2);
    OUT_BATCH(_3DSTATE_URB_VS << 16 | (2 - 2));
    OUT_BATCH(brw->urb.nr_vs_entries |
diff --git a/src/mesa/drivers/dri/i965/gen7_vs_state.c b/src/mesa/drivers/dri/i965/gen7_vs_state.c
index 0746e6c..a3d652c 100644
--- a/src/mesa/drivers/dri/i965/gen7_vs_state.c
+++ b/src/mesa/drivers/dri/i965/gen7_vs_state.c
@@ -35,6 +35,8 @@ upload_vs_state(struct brw_context *brw)
    struct intel_context *intel = &brw->intel;
    uint32_t floating_point_mode = 0;
 
+   gen7_emit_vs_workaround_flush(intel);
+
    BEGIN_BATCH(2);
    OUT_BATCH(_3DSTATE_BINDING_TABLE_POINTERS_VS << 16 | (2 - 2));
    OUT_BATCH(brw->bind.bo_offset);
diff --git a/src/mesa/drivers/dri/intel/intel_batchbuffer.c b/src/mesa/drivers/dri/intel/intel_batchbuffer.c
index c58dee8..d10e008 100644
--- a/src/mesa/drivers/dri/intel/intel_batchbuffer.c
+++ b/src/mesa/drivers/dri/intel/intel_batchbuffer.c
@@ -56,13 +56,13 @@ intel_batchbuffer_init(struct intel_context *intel)
 {
    intel_batchbuffer_reset(intel);
 
-   if (intel->gen == 6) {
+   if (intel->gen >= 6) {
       /* We can't just use brw_state_batch to get a chunk of space for
        * the gen6 workaround because it involves actually writing to
        * the buffer, and the kernel doesn't let us write to the batch.
        */
       intel->batch.workaround_bo = drm_intel_bo_alloc(intel->bufmgr,
-						      "gen6 workaround",
+						      "pipe_control workaround",
 						      4096, 4096);
    }
 }
@@ -394,6 +394,28 @@ intel_emit_depth_stall_flushes(struct intel_context *intel)
 }
 
 /**
+ * From the BSpec, volume 2a.03: VS Stage Input / State:
+ * "[DevIVB] A PIPE_CONTROL with Post-Sync Operation set to 1h and a depth
+ *  stall needs to be sent just prior to any 3DSTATE_VS, 3DSTATE_URB_VS,
+ *  3DSTATE_CONSTANT_VS, 3DSTATE_BINDING_TABLE_POINTER_VS,
+ *  3DSTATE_SAMPLER_STATE_POINTER_VS command.  Only one PIPE_CONTROL needs
+ *  to be sent before any combination of VS associated 3DSTATE."
+ */
+void
+gen7_emit_vs_workaround_flush(struct intel_context *intel)
+{
+   assert(intel->gen == 7);
+
+   BEGIN_BATCH(4);
+   OUT_BATCH(_3DSTATE_PIPE_CONTROL);
+   OUT_BATCH(PIPE_CONTROL_DEPTH_STALL | PIPE_CONTROL_WRITE_IMMEDIATE);
+   OUT_RELOC(intel->batch.workaround_bo,
+	     I915_GEM_DOMAIN_INSTRUCTION, I915_GEM_DOMAIN_INSTRUCTION, 0);
+   OUT_BATCH(0); /* write data */
+   ADVANCE_BATCH();
+}
+
+/**
  * Emits a PIPE_CONTROL with a non-zero post-sync operation, for
  * implementing two workarounds on gen6.  From section 1.4.7.1
  * "PIPE_CONTROL" of the Sandy Bridge PRM volume 2 part 1:
diff --git a/src/mesa/drivers/dri/intel/intel_batchbuffer.h b/src/mesa/drivers/dri/intel/intel_batchbuffer.h
index e5e5bd4..751ec99 100644
--- a/src/mesa/drivers/dri/intel/intel_batchbuffer.h
+++ b/src/mesa/drivers/dri/intel/intel_batchbuffer.h
@@ -43,6 +43,7 @@ bool intel_batchbuffer_emit_reloc_fenced(struct intel_context *intel,
 void intel_batchbuffer_emit_mi_flush(struct intel_context *intel);
 void intel_emit_post_sync_nonzero_flush(struct intel_context *intel);
 void intel_emit_depth_stall_flushes(struct intel_context *intel);
+void gen7_emit_vs_workaround_flush(struct intel_context *intel);
 
 static INLINE uint32_t float_as_int(float f)
 {
-- 
1.7.7.1