Quite rarely we see that the CS completion event fires before the
breadcrumb is coherent, which presumably is a result of the CS_STALL not
waiting for the post-sync operation. Try following in a DC_FLUSH into
the following pipecontrol to see if that makes any difference.

Signed-off-by: Chris Wilson <[email protected]>
Cc: Mika Kuoppala <[email protected]>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c 
b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 80a3f1dbb456..48046d445733 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -2971,6 +2971,7 @@ static u32 *gen8_emit_fini_breadcrumb_rcs(struct 
i915_request *request, u32 *cs)
        /* XXX flush+write+CS_STALL all in one upsets gem_concurrent_blt:kbl */
        cs = gen8_emit_pipe_control(cs,
                                    PIPE_CONTROL_FLUSH_ENABLE |
+                                   PIPE_CONTROL_DC_FLUSH_ENABLE |
                                    PIPE_CONTROL_CS_STALL,
                                    0);
 
-- 
2.23.0

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