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

[Jason Ekstrand]

Seems reasonable to me.  I would say we should set it in Vulkan too except
that the only way you can get a buffer size of 0 is invalid usage so meh.

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>

On Sun, Oct 8, 2017 at 7:47 PM, Kenneth Graunke <kenneth at whitecape.org>
wrote:

> 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
>
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