diff --git a/sdk/include/ddk/video.h b/sdk/include/ddk/video.h
index 1500e03bb9b..d4f32002b15 100644
--- a/sdk/include/ddk/video.h
+++ b/sdk/include/ddk/video.h
@@ -551,6 +551,14 @@ typedef enum _DMA_FLAGS {
   VideoPortDmaInitOnly
 } DMA_FLAGS;
 
+/*
+ * Data returned with VpControllerData.
+ *
+ * The first two fields, InterfaceType and BusNumber, are common
+ * with the CM_FULL_RESOURCE_DESCRIPTOR header.
+ * The other fields are of legacy layout, instead of the newer
+ * CM_PARTIAL_RESOURCE_LIST one.
+ */
 typedef struct _VIDEO_HARDWARE_CONFIGURATION_DATA {
   INTERFACE_TYPE InterfaceType;
   ULONG BusNumber;