[PATCH 1/7] no-lite-restore2

[Chris Wilson]

---
 drivers/gpu/drm/i915/intel_lrc.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 029901a8fa38..5c50263e45d3 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -639,6 +639,19 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 		if (port_count(&port[1]))
 			goto unlock;
 
+		/*
+		 * Skip invoking a lite-restore if we know we have already
+		 * started processing the last request queued to HW. This
+		 * prevents a mystery *unrecoverable* hang on gen8, maybe
+		 * related to updating TAIL within a cacheline of HEAD? (As
+		 * there is still a delay between submitting the ESLP update
+		 * and HW responding, we may still encounter whatever condition
+		 * trips up, just less often.)
+		 */
+		if (i915_seqno_passed(intel_engine_get_seqno(engine),
+				      last->global_seqno - 1))
+			goto unlock;
+
 		/*
 		 * WaIdleLiteRestore:bdw,skl
 		 * Apply the wa NOOPs to prevent
-- 
2.17.0