diff --git a/fdts/stm32mp15-fw-config.dtsi b/fdts/stm32mp15-fw-config.dtsi
index 4f2841f..8aece28 100644
--- a/fdts/stm32mp15-fw-config.dtsi
+++ b/fdts/stm32mp15-fw-config.dtsi
@@ -4,9 +4,27 @@
  */
 
 #include <common/tbbr/tbbr_img_def.h>
+#include <dt-bindings/soc/stm32mp15-tzc400.h>
 
 #include <platform_def.h>
 
+#ifndef DDR_SIZE
+#error "DDR_SIZE is not defined"
+#endif
+
+#define DDR_NS_BASE	STM32MP_DDR_BASE
+#ifdef AARCH32_SP_OPTEE
+/* OP-TEE reserved shared memory: located at DDR top */
+#define DDR_SHARE_SIZE	STM32MP_DDR_SHMEM_SIZE
+#define DDR_SHARE_BASE	(STM32MP_DDR_BASE + (DDR_SIZE - DDR_SHARE_SIZE))
+/* OP-TEE secure memory: located right below OP-TEE reserved shared memory */
+#define DDR_SEC_SIZE	STM32MP_DDR_S_SIZE
+#define DDR_SEC_BASE	(DDR_SHARE_BASE - DDR_SEC_SIZE)
+#define DDR_NS_SIZE	(DDR_SEC_BASE - DDR_NS_BASE)
+#else /* !AARCH32_SP_OPTEE */
+#define DDR_NS_SIZE	DDR_SIZE
+#endif /* AARCH32_SP_OPTEE */
+
 /dts-v1/;
 
 / {
@@ -45,4 +63,18 @@
 		};
 #endif
 	};
+
+	st-mem-firewall {
+		compatible = "st,mem-firewall";
+#ifdef AARCH32_SP_OPTEE
+		memory-ranges = <
+			DDR_NS_BASE DDR_NS_SIZE TZC_REGION_S_NONE TZC_REGION_NSEC_ALL_ACCESS_RDWR
+			DDR_SEC_BASE DDR_SEC_SIZE TZC_REGION_S_RDWR 0
+			DDR_SHARE_BASE DDR_SHARE_SIZE TZC_REGION_S_NONE
+			TZC_REGION_ACCESS_RDWR(STM32MP1_TZC_A7_ID)>;
+#else
+		memory-ranges = <
+			DDR_NS_BASE DDR_NS_SIZE TZC_REGION_S_NONE TZC_REGION_NSEC_ALL_ACCESS_RDWR>;
+#endif
+	};
 };