radeonsi: fix ARB_transform_feedback_overflow_query on <= VI

The result written by the shader workaround needs to be written back, or
the CP may read stale data.

Fixes: 78476cfe07 ("radeonsi: enable ARB_transform_feedback_overflow_query")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/drivers/radeon/r600_pipe_common.h

@@ -454,6 +454,11 @@ struct r600_common_screen {
 		 */
 		unsigned cp_to_L2;
 
+		/* Context flags to set so that all writes from earlier jobs
+		 * that end in L2 are seen by CP.
+		 */
+		unsigned L2_to_cp;
+
 		/* Context flags to set so that all writes from earlier
 		 * compute jobs are seen by L2 clients.
 		 */

src/gallium/drivers/radeon/r600_query.c

@@ -1833,6 +1833,10 @@ static void r600_render_condition(struct pipe_context *ctx,
 				ctx, query, true, PIPE_QUERY_TYPE_U64, 0,
 				&rquery->workaround_buf->b.b, rquery->workaround_offset);
 
+			/* Settings this in the render cond atom is too late,
+			 * so set it here. */
+			rctx->flags |= rctx->screen->barrier_flags.L2_to_cp;
+
 			atom->num_dw = 5;
 
 			rctx->render_cond_force_off = old_force_off;

src/gallium/drivers/radeonsi/si_pipe.c

@@ -1078,8 +1078,10 @@ struct pipe_screen *radeonsi_screen_create(struct radeon_winsys *ws,
 
 	sscreen->b.barrier_flags.cp_to_L2 = SI_CONTEXT_INV_SMEM_L1 |
 					    SI_CONTEXT_INV_VMEM_L1;
-	if (sscreen->b.chip_class <= VI)
+	if (sscreen->b.chip_class <= VI) {
 		sscreen->b.barrier_flags.cp_to_L2 |= SI_CONTEXT_INV_GLOBAL_L2;
+		sscreen->b.barrier_flags.L2_to_cp |= SI_CONTEXT_WRITEBACK_GLOBAL_L2;
+	}
 
 	sscreen->b.barrier_flags.compute_to_L2 = SI_CONTEXT_CS_PARTIAL_FLUSH;