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v3dv: route blending of UNORM16/SNORM16 RTs through software lowering

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UNORM16/SNORM16 render targets are backed by 16-bit-integer TLB
formats, which V3D HW cannot blend. The compiler already supports
software blend lowering in NIR, but V3DV only enabled it for dual-src
blending. As a result format_supports_blending refused the BLEND_BIT
for these formats and Dawn could not advertise the WebGPU
Unorm16TextureFormats feature.

Set pipeline->blend.use_software when any color attachment uses a
software-normalised format so the existing NIR blend lowering kicks
in, and expose VK_FORMAT_FEATURE_COLOR_ATTACHMENT_BLEND_BIT for
those formats.

Assisted-by: Claude Opus 4.7
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/42176>
This commit is contained in:
Jose Maria Casanova Crespo 2026-05-21 00:15:43 +02:00
parent 051ede709c
commit 4edc659231
2 changed files with 17 additions and 4 deletions
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7
src/broadcom/vulkan/v3dvx_formats.c
View file

@ -487,6 +487,13 @@ v3dX(format_supports_blending)(const struct v3dv_format *format)
if (!format->plane_count || format->plane_count > 1)
return false;
/* Software-emulated UNORM16/SNORM16 RTs use 16-bit-integer storage which
* HW can't blend, but the compiler lowers blending in NIR for them, so
* we still expose VK_FORMAT_FEATURE_COLOR_ATTACHMENT_BLEND_BIT.
*/
if (format->planes[0].unorm || format->planes[0].snorm)
return true;
/* Hardware blending is only supported on render targets that are configured
* 4x8-bit unorm, 2x16-bit float or 4x16-bit float.
*/

14
src/broadcom/vulkan/v3dvx_pipeline.c
View file

@ -97,6 +97,7 @@ pack_blend(struct v3dv_pipeline *pipeline,
uint32_t color_write_masks = 0;
bool needs_dual_src = false;
bool needs_software_blend = false;
for (uint32_t i = 0; i < ri->color_attachment_count; i++) {
const struct vk_color_blend_attachment_state *b_state =
&cb->attachments[i];
@ -119,6 +120,13 @@ pack_blend(struct v3dv_pipeline *pipeline,
assert(format->plane_count == 1);
bool dst_alpha_one = (format->planes[0].swizzle[3] == PIPE_SWIZZLE_1);
/* HW blend cannot operate on render targets configured as 16-bit
* integer (used for our software-packed UNORM16/SNORM16 formats).
* Fall back to NIR-lowered blending for those attachments.
*/
if (format->planes[0].unorm || format->planes[0].snorm)
needs_software_blend = true;
uint8_t rt_mask = 1 << i;
pipeline->blend.enables |= rt_mask;
@ -147,10 +155,8 @@ pack_blend(struct v3dv_pipeline *pipeline,
}
}
/* We may want to fallback to software in other cases in the future such
* as for formats not supported by the blend hardware.
*/
pipeline->blend.use_software = V3D_DBG(SOFT_BLEND) || needs_dual_src;
pipeline->blend.use_software =
V3D_DBG(SOFT_BLEND) || needs_dual_src || needs_software_blend;
pipeline->blend.color_write_masks = color_write_masks;
}