diff --git a/plat/arm/board/common/board_css_common.c b/plat/arm/board/common/board_css_common.c
index 42f754e..f6a554f 100644
--- a/plat/arm/board/common/board_css_common.c
+++ b/plat/arm/board/common/board_css_common.c
@@ -19,6 +19,7 @@
 	CSS_MAP_DEVICE,
 	SOC_CSS_MAP_DEVICE,
 #if TRUSTED_BOARD_BOOT
+	/* Map DRAM to authenticate NS_BL2U image. */
 	ARM_MAP_NS_DRAM1,
 #endif
 	{0}