[Mesa-dev] [PATCH] anv: Disable dual source blending when shader doesn't support it on gen8+

[Danylo Piliaiev]

bump. I can add test to Crucible if it will help.


On 20.07.18 12:54, Danylo Piliaiev wrote:
> Dual source blending behaviour is undefined when shader doesn't
> have second color output.
>
>   "If SRC1 is included in a src/dst blend factor and
>    a DualSource RT Write message is not used, results
>    are UNDEFINED. (This reflects the same restriction in DX APIs,
>    where undefined results are produced if “o1” is not written
>    by a PS – there are no default values defined)."
>
> Dismissing fragment in such situation leads to a hang on gen8+
> if depth test in enabled.
>
> Since blending cannot be gracefully fixed in such case and the result
> is undefined - blending is simply disabled.
>
> Signed-off-by: Danylo Piliaiev <danylo.piliaiev at globallogic.com>
> ---
>
> Also there is a similar patch which fixes the same issue
> for OpenGL https://patchwork.freedesktop.org/patch/235939
>
>   src/intel/vulkan/genX_pipeline.c | 43 ++++++++++++++++++++++++--------
>   1 file changed, 32 insertions(+), 11 deletions(-)
>
> diff --git a/src/intel/vulkan/genX_pipeline.c b/src/intel/vulkan/genX_pipeline.c
> index 0821d71c9f..d7c532a22d 100644
> --- a/src/intel/vulkan/genX_pipeline.c
> +++ b/src/intel/vulkan/genX_pipeline.c
> @@ -854,6 +854,15 @@ emit_ds_state(struct anv_pipeline *pipeline,
>   #endif
>   }
>   
> +MAYBE_UNUSED static bool
> +is_dual_src_blend_factor(VkBlendFactor factor)
> +{
> +   return factor == VK_BLEND_FACTOR_SRC1_COLOR ||
> +          factor == VK_BLEND_FACTOR_ONE_MINUS_SRC1_COLOR ||
> +          factor == VK_BLEND_FACTOR_SRC1_ALPHA ||
> +          factor == VK_BLEND_FACTOR_ONE_MINUS_SRC1_ALPHA;
> +}
> +
>   static void
>   emit_cb_state(struct anv_pipeline *pipeline,
>                 const VkPipelineColorBlendStateCreateInfo *info,
> @@ -886,6 +895,7 @@ emit_cb_state(struct anv_pipeline *pipeline,
>      state_pos += GENX(BLEND_STATE_length);
>   #if GEN_GEN >= 8
>      struct GENX(BLEND_STATE_ENTRY) bs0 = { 0 };
> +   bool force_disable_color_blend = false;
>   #endif
>      for (unsigned i = 0; i < surface_count; i++) {
>         struct anv_pipeline_binding *binding = &map->surface_to_descriptor[i];
> @@ -969,8 +979,27 @@ emit_cb_state(struct anv_pipeline *pipeline,
>         GENX(BLEND_STATE_ENTRY_pack)(NULL, state_pos, &entry);
>         state_pos += GENX(BLEND_STATE_ENTRY_length);
>   #if GEN_GEN >= 8
> -      if (i == 0)
> +      if (i == 0) {
>            bs0 = entry;
> +
> +         /* The Dual Source Blending documentation says:
> +          *
> +          * "If SRC1 is included in a src/dst blend factor and
> +          * a DualSource RT Write message is not used, results
> +          * are UNDEFINED. (This reflects the same restriction in DX APIs,
> +          * where undefined results are produced if “o1” is not written
> +          * by a PS – there are no default values defined)."
> +          *
> +          * There is no way to gracefully fix this undefined situation
> +          * so we just disable the blending to prevent possible issues.
> +          */
> +         const struct brw_wm_prog_data *wm_prog_data = get_wm_prog_data(pipeline);
> +         force_disable_color_blend = !wm_prog_data->dual_src_blend &&
> +            (is_dual_src_blend_factor(a->srcColorBlendFactor) ||
> +            is_dual_src_blend_factor(a->dstColorBlendFactor) ||
> +            is_dual_src_blend_factor(a->srcAlphaBlendFactor) ||
> +            is_dual_src_blend_factor(a->dstAlphaBlendFactor));
> +      }
>   #endif
>      }
>   
> @@ -978,7 +1007,8 @@ emit_cb_state(struct anv_pipeline *pipeline,
>      anv_batch_emit(&pipeline->batch, GENX(3DSTATE_PS_BLEND), blend) {
>         blend.AlphaToCoverageEnable         = blend_state.AlphaToCoverageEnable;
>         blend.HasWriteableRT                = has_writeable_rt;
> -      blend.ColorBufferBlendEnable        = bs0.ColorBufferBlendEnable;
> +      blend.ColorBufferBlendEnable        =
> +         bs0.ColorBufferBlendEnable && !force_disable_color_blend;
>         blend.SourceAlphaBlendFactor        = bs0.SourceAlphaBlendFactor;
>         blend.DestinationAlphaBlendFactor   = bs0.DestinationAlphaBlendFactor;
>         blend.SourceBlendFactor             = bs0.SourceBlendFactor;
> @@ -1430,15 +1460,6 @@ emit_3dstate_wm(struct anv_pipeline *pipeline, struct anv_subpass *subpass,
>      }
>   }
>   
> -UNUSED static bool
> -is_dual_src_blend_factor(VkBlendFactor factor)
> -{
> -   return factor == VK_BLEND_FACTOR_SRC1_COLOR ||
> -          factor == VK_BLEND_FACTOR_ONE_MINUS_SRC1_COLOR ||
> -          factor == VK_BLEND_FACTOR_SRC1_ALPHA ||
> -          factor == VK_BLEND_FACTOR_ONE_MINUS_SRC1_ALPHA;
> -}
> -
>   static void
>   emit_3dstate_ps(struct anv_pipeline *pipeline,
>                   const VkPipelineColorBlendStateCreateInfo *blend,