drm/vmwgfx: Make user resource lookups reference-free during validation

Make the process of looking up a user resource and adding it to the
validation list reference-free unless when it's actually added to the
validation list where a single reference is taken.
This saves two locked atomic operations per command stream buffer object
handle lookup, unless there is a lookup cache hit.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_resource.c

@@ -230,6 +230,41 @@ out_bad_resource:
 	return ret;
 }
 
+/**
+ * vmw_user_resource_lookup_handle - lookup a struct resource from a
+ * TTM user-space handle and perform basic type checks
+ *
+ * @dev_priv:     Pointer to a device private struct
+ * @tfile:        Pointer to a struct ttm_object_file identifying the caller
+ * @handle:       The TTM user-space handle
+ * @converter:    Pointer to an object describing the resource type
+ * @p_res:        On successful return the location pointed to will contain
+ *                a pointer to a refcounted struct vmw_resource.
+ *
+ * If the handle can't be found or is associated with an incorrect resource
+ * type, -EINVAL will be returned.
+ */
+struct vmw_resource *
+vmw_user_resource_noref_lookup_handle(struct vmw_private *dev_priv,
+				      struct ttm_object_file *tfile,
+				      uint32_t handle,
+				      const struct vmw_user_resource_conv
+				      *converter)
+{
+	struct ttm_base_object *base;
+
+	base = ttm_base_object_noref_lookup(tfile, handle);
+	if (!base)
+		return ERR_PTR(-ESRCH);
+
+	if (unlikely(ttm_base_object_type(base) != converter->object_type)) {
+		ttm_base_object_noref_release();
+		return ERR_PTR(-EINVAL);
+	}
+
+	return converter->base_obj_to_res(base);
+}
+
 /**
  * Helper function that looks either a surface or bo.
  *