radv: add RADV_DEBUG=novrsflatshading option

To easily debug if enabling VRS for flat shading is broken.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9515>

docs/envvars.rst

@@ -601,6 +601,8 @@ RADV driver environment variables
       disable LLVM threaded compilation
    ``noumr``
       disable UMR dumps during GPU hang detection (only with RADV_DEBUG=hang)
+   ``novrsflatshading``
+      disable VRS for flat shading (only on GFX10.3+)
    ``preoptir``
       dump LLVM IR before any optimizations
    ``shaders``

src/amd/vulkan/radv_debug.h

@@ -62,6 +62,7 @@ enum {
 	RADV_DEBUG_INVARIANT_GEOM    = 1ull << 31,
 	RADV_DEBUG_NO_DISPLAY_DCC    = 1ull << 32,
 	RADV_DEBUG_NO_TC_COMPAT_CMASK= 1ull << 33,
+	RADV_DEBUG_NO_VRS_FLAT_SHADING = 1ull << 34,
 };
 
 enum {

src/amd/vulkan/radv_device.c

@@ -797,6 +797,7 @@ static const struct debug_control radv_debug_options[] = {
 	{"invariantgeom", RADV_DEBUG_INVARIANT_GEOM},
 	{"nodisplaydcc", RADV_DEBUG_NO_DISPLAY_DCC},
 	{"notccompatcmask", RADV_DEBUG_NO_TC_COMPAT_CMASK},
+	{"novrsflatshading", RADV_DEBUG_NO_VRS_FLAT_SHADING},
 	{NULL, 0}
 };
 

src/amd/vulkan/radv_pipeline.c

@@ -5312,6 +5312,10 @@ static bool
 gfx103_pipeline_vrs_coarse_shading(const struct radv_pipeline *pipeline)
 {
 	struct radv_shader_variant *ps = pipeline->shaders[MESA_SHADER_FRAGMENT];
+	struct radv_device *device = pipeline->device;
+
+	if (device->instance->debug_flags & RADV_DEBUG_NO_VRS_FLAT_SHADING)
+		return false;
 
 	if (!ps->info.ps.allow_flat_shading)
 		return false;