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}
diff --git a/plat/arm/board/fvp/fvp_common.c b/plat/arm/board/fvp/fvp_common.c
index eb37f11..2f5d7fc 100644
--- a/plat/arm/board/fvp/fvp_common.c
+++ b/plat/arm/board/fvp/fvp_common.c
@@ -36,6 +36,10 @@
 					DEVICE1_SIZE,			\
 					MT_DEVICE | MT_RW | MT_SECURE)
 
+/*
+ * Need to be mapped with write permissions in order to set a new non-volatile
+ * counter value.
+ */
 #define MAP_DEVICE2	MAP_REGION_FLAT(DEVICE2_BASE,			\
 					DEVICE2_SIZE,			\
 					MT_DEVICE | MT_RW | MT_SECURE)
@@ -56,8 +60,10 @@
 	V2M_MAP_IOFPGA,
 	MAP_DEVICE0,
 	MAP_DEVICE1,
-	MAP_DEVICE2,
 #if TRUSTED_BOARD_BOOT
+	/* To access the Root of Trust Public Key registers. */
+	MAP_DEVICE2,
+	/* Map DRAM to authenticate NS_BL2U image. */
 	ARM_MAP_NS_DRAM1,
 #endif
 	{0}
@@ -70,9 +76,12 @@
 	V2M_MAP_IOFPGA,
 	MAP_DEVICE0,
 	MAP_DEVICE1,
-	MAP_DEVICE2,
 	ARM_MAP_NS_DRAM1,
 	ARM_MAP_TSP_SEC_MEM,
+#if TRUSTED_BOARD_BOOT
+	/* To access the Root of Trust Public Key registers. */
+	MAP_DEVICE2,
+#endif
 #if ARM_BL31_IN_DRAM
 	ARM_MAP_BL31_SEC_DRAM,
 #endif