drm/i915: inline vma_create into lookup_or_create_vma

In the execbuf code we don't clean up any vmas which ended up not
getting bound for code simplicity. To make sure that we don't end up
creating multiple vma for the same vm kill the somewhat dangerous
vma_create function and inline it into lookup_or_create.

This is just a safety measure to prevent surprises in the future.

Also update the somewhat confused comment in the execbuf code and
clarify what kind of magic is going on with a new one.

v2: Keep the function separate as requested by Chris. But give it a __
prefix for paranoia and move it tighter together with the other vma
stuff.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ben Widawsky <ben@bwidawsk.net>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index c4c56f9..6820d0a 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4109,9 +4109,20 @@
 	i915_gem_object_free(obj);
 }
 
-struct i915_vma *i915_gem_vma_create(struct drm_i915_gem_object *obj,
+struct i915_vma *i915_gem_obj_to_vma(struct drm_i915_gem_object *obj,
 				     struct i915_address_space *vm)
 {
+	struct i915_vma *vma;
+	list_for_each_entry(vma, &obj->vma_list, vma_link)
+		if (vma->vm == vm)
+			return vma;
+
+	return NULL;
+}
+
+static struct i915_vma *__i915_gem_vma_create(struct drm_i915_gem_object *obj,
+					      struct i915_address_space *vm)
+{
 	struct i915_vma *vma = kzalloc(sizeof(*vma), GFP_KERNEL);
 	if (vma == NULL)
 		return ERR_PTR(-ENOMEM);
@@ -4131,6 +4142,19 @@
 	return vma;
 }
 
+struct i915_vma *
+i915_gem_obj_lookup_or_create_vma(struct drm_i915_gem_object *obj,
+				  struct i915_address_space *vm)
+{
+	struct i915_vma *vma;
+
+	vma = i915_gem_obj_to_vma(obj, vm);
+	if (!vma)
+		vma = __i915_gem_vma_create(obj, vm);
+
+	return vma;
+}
+
 void i915_gem_vma_destroy(struct i915_vma *vma)
 {
 	WARN_ON(vma->node.allocated);
@@ -4857,27 +4881,3 @@
 
 	return 0;
 }
-
-struct i915_vma *i915_gem_obj_to_vma(struct drm_i915_gem_object *obj,
-				     struct i915_address_space *vm)
-{
-	struct i915_vma *vma;
-	list_for_each_entry(vma, &obj->vma_list, vma_link)
-		if (vma->vm == vm)
-			return vma;
-
-	return NULL;
-}
-
-struct i915_vma *
-i915_gem_obj_lookup_or_create_vma(struct drm_i915_gem_object *obj,
-				  struct i915_address_space *vm)
-{
-	struct i915_vma *vma;
-
-	vma = i915_gem_obj_to_vma(obj, vm);
-	if (!vma)
-		vma = i915_gem_vma_create(obj, vm);
-
-	return vma;
-}