drm/fence: add drm_crtc_create_fence()

Instead of dealing with crtc details inside drm_atomic.c we should
just export a function that creates a new crtc fence for us and
use that.

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1481046437-18778-1-git-send-email-gustavo@padovan.org
diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 19d7bcb..72fa5b2 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -1864,20 +1864,6 @@ EXPORT_SYMBOL(drm_atomic_clean_old_fb);
  *	helpers and for the DRM event handling for existing userspace.
  */
 
-static struct dma_fence *get_crtc_fence(struct drm_crtc *crtc)
-{
-	struct dma_fence *fence;
-
-	fence = kzalloc(sizeof(*fence), GFP_KERNEL);
-	if (!fence)
-		return NULL;
-
-	dma_fence_init(fence, &drm_crtc_fence_ops, &crtc->fence_lock,
-		       crtc->fence_context, ++crtc->fence_seqno);
-
-	return fence;
-}
-
 struct drm_out_fence_state {
 	s64 __user *out_fence_ptr;
 	struct sync_file *sync_file;
@@ -1959,7 +1945,7 @@ static int prepare_crtc_signaling(struct drm_device *dev,
 			f[*num_fences].out_fence_ptr = fence_ptr;
 			*fence_state = f;
 
-			fence = get_crtc_fence(crtc);
+			fence = drm_crtc_create_fence(crtc);
 			if (!fence)
 				return -ENOMEM;