diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 3c9da1f8979e3aaf0e2cd99a3637eb47c876d7d9..20b592dec335ca32e08138ab0a8686881537c8fb 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -605,6 +605,10 @@ struct iommu_group *fsl_mc_device_group(struct device *dev);
  * @flags: IOMMU_FWSPEC_* flags
  * @num_ids: number of associated device IDs
  * @ids: IDs which this device may present to the IOMMU
+ *
+ * Note that the IDs (and any other information, really) stored in this structure should be
+ * considered private to the IOMMU device driver and are not to be used directly by IOMMU
+ * consumers.
  */
 struct iommu_fwspec {
 	const struct iommu_ops	*ops;