drm/i915: Consolidate get_fence with pin_fence

Following the pattern now used for obj->mm.pages, use just pin_fence and
unpin_fence to control access to the fence registers. I.e. instead of
calling get_fence(); pin_fence(), we now just need to call pin_fence().
This will make it easier to reduce the locking requirements around
fence registers.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171009084401.29090-2-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index eba23c2..37eba9d 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1910,7 +1910,7 @@ int i915_gem_fault(struct vm_fault *vmf)
 	if (ret)
 		goto err_unpin;
 
-	ret = i915_vma_get_fence(vma);
+	ret = i915_vma_pin_fence(vma);
 	if (ret)
 		goto err_unpin;
 
@@ -1926,6 +1926,7 @@ int i915_gem_fault(struct vm_fault *vmf)
 			       min_t(u64, vma->size, area->vm_end - area->vm_start),
 			       &ggtt->mappable);
 
+	i915_vma_unpin_fence(vma);
 err_unpin:
 	__i915_vma_unpin(vma);
 err_unlock: