lavapipe: add option to enable snorm blending

This is disabled by default because it fails CTS, however this may
still be useful (as it generally works), hence use LVP_SNORM_BLEND
env var to enable it.

Acked-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Brian Paul <brian.paul@broadcom.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29587>

src/gallium/frontends/lavapipe/lvp_device.c

@@ -1238,6 +1238,9 @@ lvp_physical_device_init(struct lvp_physical_device *device,
       device->vk.supported_extensions.EXT_image_drm_format_modifier = true;
 #endif
 
+   /* SNORM blending on llvmpipe fails CTS - disable by default */
+   device->snorm_blend = debug_get_bool_option("LVP_SNORM_BLEND", false);
+
    lvp_get_features(device, &device->vk.supported_features);
    lvp_get_properties(device, &device->vk.properties);
 

src/gallium/frontends/lavapipe/lvp_formats.c

@@ -162,9 +162,8 @@ lvp_physical_device_get_format_properties(struct lvp_physical_device *physical_d
    if (pscreen->is_format_supported(pscreen, pformat, PIPE_TEXTURE_2D, 0, 0,
                                     PIPE_BIND_RENDER_TARGET)) {
       features |= VK_FORMAT_FEATURE_2_COLOR_ATTACHMENT_BIT;
-      /* SNORM blending on llvmpipe fails CTS - disable for now */
-      if (!util_format_is_snorm(pformat) &&
-          !util_format_is_pure_integer(pformat))
+      if (!util_format_is_pure_integer(pformat) &&
+          !(util_format_is_snorm(pformat) && !physical_device->snorm_blend))
          features |= VK_FORMAT_FEATURE_2_COLOR_ATTACHMENT_BLEND_BIT;
    }
 

src/gallium/frontends/lavapipe/lvp_private.h

@@ -153,6 +153,7 @@ struct lvp_physical_device {
    struct pipe_screen *pscreen;
    const nir_shader_compiler_options *drv_options[LVP_SHADER_STAGES];
    uint32_t max_images;
+   bool snorm_blend;
 
    struct vk_sync_timeline_type sync_timeline_type;
    const struct vk_sync_type *sync_types[3];