drm/i915: Add convenience wrappers for vma's object get/put

The VMA are unreferenced, they belong to the object and live until they
are closed. However, if we want to use the VMA as a cookie and use it to
keep the object alive, we want to hold onto a reference to the object
for the lifetime of the VMA cookie. To facilitate this, add a couple of
simple wrappers for managing the reference count on the object owning the
VMA.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471254551-25805-11-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -2373,6 +2373,18 @@ i915_gem_object_get_stride(struct drm_i915_gem_object *obj)
 	return obj->tiling_and_stride & STRIDE_MASK;
 }
 
+static inline struct i915_vma *i915_vma_get(struct i915_vma *vma)
+{
+	i915_gem_object_get(vma->obj);
+	return vma;
+}
+
+static inline void i915_vma_put(struct i915_vma *vma)
+{
+	lockdep_assert_held(&vma->vm->dev->struct_mutex);
+	i915_gem_object_put(vma->obj);
+}
+
 /*
  * Optimised SGL iterator for GEM objects
  */

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -271,7 +271,7 @@ static void eb_destroy(struct eb_vmas *eb)
 				       exec_list);
 		list_del_init(&vma->exec_list);
 		i915_gem_execbuffer_unreserve_vma(vma);
-		i915_gem_object_put(vma->obj);
+		i915_vma_put(vma);
 	}
 	kfree(eb);
 }
@@ -900,7 +900,7 @@ i915_gem_execbuffer_relocate_slow(struct drm_device *dev,
 		vma = list_first_entry(&eb->vmas, struct i915_vma, exec_list);
 		list_del_init(&vma->exec_list);
 		i915_gem_execbuffer_unreserve_vma(vma);
-		i915_gem_object_put(vma->obj);
+		i915_vma_put(vma);
 	}
 
 	mutex_unlock(&dev->struct_mutex);