drm/i915: Initialise basic fence before acquiring seqno

Inside the intel_timeline_get_seqno(), we currently track the retirement
of the old cachelines by listening to the new request. This requires
that the new request is ready to be used and so requires a minimum bit
of initialisation prior to getting the new seqno.

Fixes: b1e3177b ("drm/i915: Coordinate i915_active with its own mutex")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200203094152.4150550-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_request.c

@@ -595,6 +595,8 @@ static void __i915_request_ctor(void *arg)
 	i915_sw_fence_init(&rq->submit, submit_notify);
 	i915_sw_fence_init(&rq->semaphore, semaphore_notify);
 
+	dma_fence_init(&rq->fence, &i915_fence_ops, &rq->lock, 0, 0);
+
 	rq->file_priv = NULL;
 	rq->capture_list = NULL;
 
@@ -653,25 +655,30 @@ __i915_request_create(struct intel_context *ce, gfp_t gfp)
 		}
 	}
 
-	ret = intel_timeline_get_seqno(tl, rq, &seqno);
-	if (ret)
-		goto err_free;
-
 	rq->i915 = ce->engine->i915;
 	rq->context = ce;
 	rq->engine = ce->engine;
 	rq->ring = ce->ring;
 	rq->execution_mask = ce->engine->mask;
 
+	kref_init(&rq->fence.refcount);
+	rq->fence.flags = 0;
+	rq->fence.error = 0;
+	INIT_LIST_HEAD(&rq->fence.cb_list);
+
+	ret = intel_timeline_get_seqno(tl, rq, &seqno);
+	if (ret)
+		goto err_free;
+
+	rq->fence.context = tl->fence_context;
+	rq->fence.seqno = seqno;
+
 	RCU_INIT_POINTER(rq->timeline, tl);
 	RCU_INIT_POINTER(rq->hwsp_cacheline, tl->hwsp_cacheline);
 	rq->hwsp_seqno = tl->hwsp_seqno;
 
 	rq->rcustate = get_state_synchronize_rcu(); /* acts as smp_mb() */
 
-	dma_fence_init(&rq->fence, &i915_fence_ops, &rq->lock,
-		       tl->fence_context, seqno);
-
 	/* We bump the ref for the fence chain */
 	i915_sw_fence_reinit(&i915_request_get(rq)->submit);
 	i915_sw_fence_reinit(&i915_request_get(rq)->semaphore);