[PATCH 02/10] drm/i915/gt: Don't declare hangs if engine is stalled

[Chris Wilson]

If the ring submission is stalled on an external request, nothing can be
submitted, not even the heartbeat in the kernel context. Since nothing
is running, resetting the engine/device does not unblock the system and
is pointless. We can see if the heartbeat is supposed to be running
before declaring foul.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 .../gpu/drm/i915/gt/intel_engine_heartbeat.c   | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c b/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
index 5136c8bf112d..a68052c1c850 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
@@ -48,8 +48,10 @@ static void show_heartbeat(const struct i915_request *rq,
 	struct drm_printer p = drm_debug_printer("heartbeat");
 
 	intel_engine_dump(engine, &p,
-			  "%s heartbeat {prio:%d} not ticking\n",
+			  "%s heartbeat {seqno:%llx:%lld, prio:%d} not ticking\n",
 			  engine->name,
+			  rq->fence.context,
+			  rq->fence.seqno,
 			  rq->sched.attr.priority);
 }
 
@@ -64,6 +66,7 @@ static void heartbeat(struct work_struct *wrk)
 	struct i915_request *rq;
 
 	rq = engine->heartbeat.systole;
+
 	if (rq && i915_request_completed(rq)) {
 		i915_request_put(rq);
 		engine->heartbeat.systole = NULL;
@@ -76,7 +79,18 @@ static void heartbeat(struct work_struct *wrk)
 		goto out;
 
 	if (engine->heartbeat.systole) {
-		if (engine->schedule &&
+		if (!i915_sw_fence_signaled(&rq->submit)) {
+			/*
+			 * Not yet submitted, system is stalled.
+			 *
+			 * This more often happens for ring submission,
+			 * where all contexts are funnelled into a common
+			 * ringbuffer. If one context is blocked on an
+			 * external fence, not only is it not submitted,
+			 * but all other contexts, including the kernel
+			 * context are stuck waiting for the signal.
+			 */
+		} else if (engine->schedule &&
 		    rq->sched.attr.priority < I915_PRIORITY_BARRIER) {
 			/*
 			 * Gradually raise the priority of the heartbeat to
-- 
2.20.1