[Mesa-dev] [PATCH] i965: Set 3DSTATE_VERTEX_BUFFER::Null Vertex Buffer.

[Kenneth Graunke]

According to the Broadwell VERTEX_BUFFER_STATE documentation,

   "VERTEX_BUFFER_STATE.Null Vertex Buffer must be set when the
    VERTEX_BUFFER_STATE.Buffer Size is 0x0.
---
 src/intel/blorp/blorp_genX_exec.h             | 2 ++
 src/mesa/drivers/dri/i965/genX_state_upload.c | 5 ++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

I'm not sure why anyone would ever /use/ a vertex buffer of size 0,
but...easy enough to follow the required programming...

diff --git a/src/intel/blorp/blorp_genX_exec.h b/src/intel/blorp/blorp_genX_exec.h
index 53892620986..e3fb6d9ae5f 100644
--- a/src/intel/blorp/blorp_genX_exec.h
+++ b/src/intel/blorp/blorp_genX_exec.h
@@ -280,6 +280,7 @@ blorp_emit_vertex_buffers(struct blorp_batch *batch,
    vb[0].BufferAccessType = VERTEXDATA;
    vb[0].EndAddress = vb[0].BufferStartingAddress;
    vb[0].EndAddress.offset += size - 1;
+   vb[0].NullVertexBuffer = size == 0;
 #elif GEN_GEN == 4
    vb[0].BufferAccessType = VERTEXDATA;
    vb[0].MaxIndex = 2;
@@ -301,6 +302,7 @@ blorp_emit_vertex_buffers(struct blorp_batch *batch,
    vb[1].BufferAccessType = INSTANCEDATA;
    vb[1].EndAddress = vb[1].BufferStartingAddress;
    vb[1].EndAddress.offset += size - 1;
+   vb[1].NullVertexBuffer = size == 0;
 #elif GEN_GEN == 4
    vb[1].BufferAccessType = INSTANCEDATA;
    vb[1].MaxIndex = 0;
diff --git a/src/mesa/drivers/dri/i965/genX_state_upload.c b/src/mesa/drivers/dri/i965/genX_state_upload.c
index ecf5a9ae68d..7fe1f12d5ed 100644
--- a/src/mesa/drivers/dri/i965/genX_state_upload.c
+++ b/src/mesa/drivers/dri/i965/genX_state_upload.c
@@ -317,12 +317,14 @@ genX(emit_vertex_buffer_state)(struct brw_context *brw,
                                unsigned stride,
                                unsigned step_rate)
 {
+   UNUSED unsigned size = end_offset - start_offset;
+
    struct GENX(VERTEX_BUFFER_STATE) buf_state = {
       .VertexBufferIndex = buffer_nr,
       .BufferPitch = stride,
       .BufferStartingAddress = ro_bo(bo, start_offset),
 #if GEN_GEN >= 8
-      .BufferSize = end_offset - start_offset,
+      .BufferSize = size,
 #endif
 
 #if GEN_GEN >= 7
@@ -334,6 +336,7 @@ genX(emit_vertex_buffer_state)(struct brw_context *brw,
       .InstanceDataStepRate = step_rate,
 #if GEN_GEN >= 5
       .EndAddress = ro_bo(bo, end_offset - 1),
+      .NullVertexBuffer = size == 0,
 #endif
 #endif
 
-- 
2.14.2