[Mesa-dev] [PATCH 1/2] radeonsi: fix a GPU hang with tessellation on 2-CU configs

[Marek Olšák]

From: Marek Olšák <marek.olsak at amd.com>

Only harvested Stoney has 2 CUs, but I couldn't test that and the bug
reporter hasn't tested it on Stoney yet. However, I reproduced the hang
on Fiji limited to 2 CUs per SE, which is how I was able to fix it.

Cc: 17.0 17.1 <mesa-stable at lists.freedesktop.org>
---
 src/gallium/drivers/radeonsi/si_state_draw.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/gallium/drivers/radeonsi/si_state_draw.c b/src/gallium/drivers/radeonsi/si_state_draw.c
index 8651592..77df643 100644
--- a/src/gallium/drivers/radeonsi/si_state_draw.c
+++ b/src/gallium/drivers/radeonsi/si_state_draw.c
@@ -162,22 +162,26 @@ static void si_emit_derived_tess_state(struct si_context *sctx,
 	output_patch_size = pervertex_output_patch_size + num_tcs_patch_outputs * 16;
 
 	/* Ensure that we only need one wave per SIMD so we don't need to check
 	 * resource usage. Also ensures that the number of tcs in and out
 	 * vertices per threadgroup are at most 256.
 	 */
 	*num_patches = 64 / MAX2(num_tcs_input_cp, num_tcs_output_cp) * 4;
 
 	/* Make sure that the data fits in LDS. This assumes the shaders only
 	 * use LDS for the inputs and outputs.
+	 *
+	 * While CIK can use 64K per threadgroup, there is a hang on Stoney
+	 * with 2 CUs if we use more than 32K. The closed Vulkan driver also
+	 * uses 32K at most on all GCN chips.
 	 */
-	hardware_lds_size = sctx->b.chip_class >= CIK ? 65536 : 32768;
+	hardware_lds_size = 32768;
 	*num_patches = MIN2(*num_patches, hardware_lds_size / (input_patch_size +
 	                                                       output_patch_size));
 
 	/* Make sure the output data fits in the offchip buffer */
 	*num_patches = MIN2(*num_patches,
 			    (sctx->screen->tess_offchip_block_dw_size * 4) /
 			    output_patch_size);
 
 	/* Not necessary for correctness, but improves performance. The
 	 * specific value is taken from the proprietary driver.
-- 
2.7.4