[Mesa-dev] [PATCH v3 28/43] anv/cmd_buffer: Add a padding to the vertex buffer

[Pohjolainen, Topi]

On Thu, Oct 12, 2017 at 08:38:17PM +0200, Jose Maria Casanova Crespo wrote:
> From: Alejandro Piñeiro <apinheiro at igalia.com>
> 
> As we are using 32-bit surface formats with 16-bit elements we can be
> on a situation where a vertex element can poke over the buffer by 2
> bytes. To avoid that we add a padding when flushing the state.
> 
> This is similar to what the i965 drivers prior to Haswell do, as they
> use 4-component formats to fake 3-component formats, and add a padding
> there too. See commit:
>    7c8dfa78b98a12c1c5f74d11433c8554d4c90657
> ---
>  src/intel/vulkan/genX_cmd_buffer.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/src/intel/vulkan/genX_cmd_buffer.c b/src/intel/vulkan/genX_cmd_buffer.c
> index 43437c8eb0..f3ba0108f4 100644
> --- a/src/intel/vulkan/genX_cmd_buffer.c
> +++ b/src/intel/vulkan/genX_cmd_buffer.c
> @@ -1958,6 +1958,11 @@ genX(cmd_buffer_flush_state)(struct anv_cmd_buffer *cmd_buffer)
>  {
>     struct anv_pipeline *pipeline = cmd_buffer->state.pipeline;
>     uint32_t *p;
> +#if GEN_GEN >= 8
> +   const struct brw_vs_prog_data *vs_prog_data = get_vs_prog_data(pipeline);
> +   const uint64_t half_inputs_read = vs_prog_data->half_inputs_read;
> +   const uint32_t elements_half = half_inputs_read >> VERT_ATTRIB_GENERIC0;
> +#endif
>  
>     uint32_t vb_emit = cmd_buffer->state.vb_dirty & pipeline->vb_used;
>  
> @@ -1970,6 +1975,17 @@ genX(cmd_buffer_flush_state)(struct anv_cmd_buffer *cmd_buffer)
>     if (vb_emit) {
>        const uint32_t num_buffers = __builtin_popcount(vb_emit);
>        const uint32_t num_dwords = 1 + num_buffers * 4;
> +      /* ISL 16-bit formats do a 16-bit to 32-bit float conversion, so we need
> +       * to use ISL 32-bit formats to avoid such conversion in order to support
> +       * properly 16-bit formats. This means that the vertex element may poke
> +       * over the end of the buffer by 2 bytes.
> +       */
> +      const unsigned padding =
> +#if GEN_GEN >= 8
> +         (elements_half > 0) * 2;
> +#else
> +      0;
> +#endif
>  
>        p = anv_batch_emitn(&cmd_buffer->batch, num_dwords,
>                            GENX(3DSTATE_VERTEX_BUFFERS));
> @@ -1999,9 +2015,9 @@ genX(cmd_buffer_flush_state)(struct anv_cmd_buffer *cmd_buffer)
>              .BufferStartingAddress = { buffer->bo, buffer->offset + offset },
>  
>  #if GEN_GEN >= 8
> -            .BufferSize = buffer->size - offset
> +            .BufferSize = buffer->size - offset + padding,

I can't help thinking that the padding should have been taken into account
by the time of allocation of the vertex buffer and marked there into ::size.
Also I'm thinking if offset needs a treatment as well. We use 32-bit formats
adn therefore the offset needs to be 32-bit aligned, right? Or does that get
guaranteed by something else (and therefore just add an assert here)?

Jason, any thoughts?

>  #else
> -            .EndAddress = { buffer->bo, buffer->offset + buffer->size - 1},
> +            .EndAddress = { buffer->bo, buffer->offset + buffer->size + padding - 1},
>  #endif
>           };
>  
> -- 
> 2.13.6
> 
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