[Mesa-dev] [PATCH 1/4] radv: don't emit no color formats.

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

If we had no rasterization, we'd emit SPI color
format as all 0's the hw dislikes this, add the workaround
from radeonsi.

Found while debugging tessellation

Signed-off-by: Dave Airlie <airlied at redhat.com>
---
 src/amd/vulkan/radv_cmd_buffer.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/amd/vulkan/radv_cmd_buffer.c b/src/amd/vulkan/radv_cmd_buffer.c
index d13becf..527184f 100644
--- a/src/amd/vulkan/radv_cmd_buffer.c
+++ b/src/amd/vulkan/radv_cmd_buffer.c
@@ -757,7 +757,24 @@ radv_emit_fragment_shader(struct radv_cmd_buffer *cmd_buffer,
 			       ps->info.fs.writes_z ? V_028710_SPI_SHADER_32_R :
 			       V_028710_SPI_SHADER_ZERO);
 
-	radeon_set_context_reg(cmd_buffer->cs, R_028714_SPI_SHADER_COL_FORMAT, blend->spi_shader_col_format);
+	/* Ensure that some export memory is always allocated, for two reasons:
+	 *
+	 * 1) Correctness: The hardware ignores the EXEC mask if no export
+	 *    memory is allocated, so KILL and alpha test do not work correctly
+	 *    without this.
+	 * 2) Performance: Every shader needs at least a NULL export, even when
+	 *    it writes no color/depth output. The NULL export instruction
+	 *    stalls without this setting.
+	 *
+	 * Don't add this to CB_SHADER_MASK.
+	 */
+	unsigned spi_shader_col_format = blend->spi_shader_col_format;
+	if (!spi_shader_col_format &&
+	    !ps->info.fs.writes_z &&
+	    !ps->info.fs.writes_stencil &&
+	    !ps->info.fs.writes_sample_mask)
+		spi_shader_col_format = V_028714_SPI_SHADER_32_R;
+	radeon_set_context_reg(cmd_buffer->cs, R_028714_SPI_SHADER_COL_FORMAT, spi_shader_col_format);
 
 	radeon_set_context_reg(cmd_buffer->cs, R_028238_CB_TARGET_MASK, blend->cb_target_mask);
 	radeon_set_context_reg(cmd_buffer->cs, R_02823C_CB_SHADER_MASK, blend->cb_shader_mask);
-- 
2.9.3