drm/i915: Remove the impedance mismatch around intel_engine_enable_signaling

There is some redundancy between dma_fence->ops->enable_signaling (via
i915_fence_enable_signaling) and our backend,
intel_engine_enable_signaling() in that both levels recheck the fence
status multiple times. If we convert intel_engine_enable_signaling() to
return the information desired by dma_fence->ops->enable_signaling, we
can reduce i915_fence_enable_signaling to a simple stub and avoid
trying to reinterpret the same information.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Michal Winiarski <michal.winiarski@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180308140732.25090-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_request.c

@@ -59,11 +59,7 @@ static bool i915_fence_signaled(struct dma_fence *fence)
 
 static bool i915_fence_enable_signaling(struct dma_fence *fence)
 {
-	if (i915_fence_signaled(fence))
-		return false;
-
-	intel_engine_enable_signaling(to_request(fence), true);
-	return !i915_fence_signaled(fence);
+	return intel_engine_enable_signaling(to_request(fence), true);
 }
 
 static signed long i915_fence_wait(struct dma_fence *fence,

drivers/gpu/drm/i915/intel_breadcrumbs.c

@@ -730,10 +730,11 @@ static void insert_signal(struct intel_breadcrumbs *b,
 	list_add(&request->signaling.link, &iter->signaling.link);
 }
 
-void intel_engine_enable_signaling(struct i915_request *request, bool wakeup)
+bool intel_engine_enable_signaling(struct i915_request *request, bool wakeup)
 {
 	struct intel_engine_cs *engine = request->engine;
 	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+	struct intel_wait *wait = &request->signaling.wait;
 	u32 seqno;
 
 	/*
@@ -750,12 +751,12 @@ void intel_engine_enable_signaling(struct i915_request *request, bool wakeup)
 
 	seqno = i915_request_global_seqno(request);
 	if (!seqno) /* will be enabled later upon execution */
-		return;
+		return true;
 
-	GEM_BUG_ON(request->signaling.wait.seqno);
-	request->signaling.wait.tsk = b->signaler;
-	request->signaling.wait.request = request;
-	request->signaling.wait.seqno = seqno;
+	GEM_BUG_ON(wait->seqno);
+	wait->tsk = b->signaler;
+	wait->request = request;
+	wait->seqno = seqno;
 
 	/*
 	 * Add ourselves into the list of waiters, but registering our
@@ -768,11 +769,15 @@ void intel_engine_enable_signaling(struct i915_request *request, bool wakeup)
 	 */
 	spin_lock(&b->rb_lock);
 	insert_signal(b, request, seqno);
-	wakeup &= __intel_engine_add_wait(engine, &request->signaling.wait);
+	wakeup &= __intel_engine_add_wait(engine, wait);
 	spin_unlock(&b->rb_lock);
 
-	if (wakeup)
+	if (wakeup) {
 		wake_up_process(b->signaler);
+		return !intel_wait_complete(wait);
+	}
+
+	return true;
 }
 
 void intel_engine_cancel_signaling(struct i915_request *request)

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -940,7 +940,7 @@ bool intel_engine_add_wait(struct intel_engine_cs *engine,
 			   struct intel_wait *wait);
 void intel_engine_remove_wait(struct intel_engine_cs *engine,
 			      struct intel_wait *wait);
-void intel_engine_enable_signaling(struct i915_request *request, bool wakeup);
+bool intel_engine_enable_signaling(struct i915_request *request, bool wakeup);
 void intel_engine_cancel_signaling(struct i915_request *request);
 
 static inline bool intel_engine_has_waiter(const struct intel_engine_cs *engine)