diff --git a/plat/st/stm32mp1/stm32mp1_security.c b/plat/st/stm32mp1/stm32mp1_security.c
index 195b3a5..6dbf6f8 100644
--- a/plat/st/stm32mp1/stm32mp1_security.c
+++ b/plat/st/stm32mp1/stm32mp1_security.c
@@ -27,6 +27,42 @@
 	TZC_REGION_ACCESS_RDWR(STM32MP1_TZC_ETH_ID) | \
 	TZC_REGION_ACCESS_RDWR(STM32MP1_TZC_DAP_ID)
 
+static unsigned int region_nb;
+
+static void init_tzc400_begin(void)
+{
+	tzc400_init(STM32MP1_TZC_BASE);
+	tzc400_disable_filters();
+
+	region_nb = 1U;
+}
+
+static void init_tzc400_end(unsigned int action)
+{
+	tzc400_set_action(action);
+	tzc400_enable_filters();
+}
+
+static void tzc400_add_region(unsigned long long region_base,
+			      unsigned long long region_top, bool sec)
+{
+	unsigned int sec_attr;
+	unsigned int nsaid_permissions;
+
+	if (sec) {
+		sec_attr = TZC_REGION_S_RDWR;
+		nsaid_permissions = 0;
+	} else {
+		sec_attr = TZC_REGION_S_NONE;
+		nsaid_permissions = TZC_REGION_NSEC_ALL_ACCESS_RDWR;
+	}
+
+	tzc400_configure_region(STM32MP1_FILTER_BIT_ALL, region_nb, region_base,
+				region_top, sec_attr, nsaid_permissions);
+
+	region_nb++;
+}
+
 /*******************************************************************************
  * Initialize the TrustZone Controller. Configure Region 0 with Secure RW access
  * and allow Non-Secure masters full access.
@@ -38,10 +74,9 @@
 	unsigned long long ddr_ns_size =
 		(unsigned long long)stm32mp_get_ddr_ns_size();
 	unsigned long long ddr_ns_top = ddr_base + (ddr_ns_size - 1U);
+	unsigned long long ddr_top __unused;
 
-	tzc400_init(STM32MP1_TZC_BASE);
-
-	tzc400_disable_filters();
+	init_tzc400_begin();
 
 	/*
 	 * Region 1 set to cover all non-secure DRAM at 0xC000_0000. Apply the
@@ -49,35 +84,28 @@
 	 */
 	region_base = ddr_base;
 	region_top = ddr_ns_top;
-	tzc400_configure_region(STM32MP1_FILTER_BIT_ALL, 1,
-				region_base,
-				region_top,
-				TZC_REGION_S_NONE,
-				TZC_REGION_NSEC_ALL_ACCESS_RDWR);
+	tzc400_add_region(region_base, region_top, false);
 
 #ifdef AARCH32_SP_OPTEE
 	/* Region 2 set to cover all secure DRAM. */
 	region_base = region_top + 1U;
 	region_top += STM32MP_DDR_S_SIZE;
-	tzc400_configure_region(STM32MP1_FILTER_BIT_ALL, 2,
-				region_base,
-				region_top,
-				TZC_REGION_S_RDWR,
-				0);
+	tzc400_add_region(region_base, region_top, true);
 
-	/* Region 3 set to cover non-secure shared memory DRAM. */
-	region_base = region_top + 1U;
-	region_top += STM32MP_DDR_SHMEM_SIZE;
-	tzc400_configure_region(STM32MP1_FILTER_BIT_ALL, 3,
-				region_base,
-				region_top,
-				TZC_REGION_S_NONE,
-				TZC_REGION_NSEC_ALL_ACCESS_RDWR);
+	ddr_top = STM32MP_DDR_BASE + dt_get_ddr_size() - 1U;
+	if (region_top < ddr_top) {
+		/* Region 3 set to cover non-secure memory DRAM after BL32. */
+		region_base = region_top + 1U;
+		region_top = ddr_top;
+		tzc400_add_region(region_base, region_top, false);
+	}
 #endif
 
-	tzc400_set_action(TZC_ACTION_INT);
-
-	tzc400_enable_filters();
+	/*
+	 * Raise an interrupt (secure FIQ) if a NS device tries to access
+	 * secure memory
+	 */
+	init_tzc400_end(TZC_ACTION_INT);
 }
 
 /*******************************************************************************
@@ -90,9 +118,7 @@
 	stm32mp_clk_enable(TZC1);
 	stm32mp_clk_enable(TZC2);
 
-	tzc400_init(STM32MP1_TZC_BASE);
-
-	tzc400_disable_filters();
+	init_tzc400_begin();
 
 	/* Region 1 set to cover Non-Secure DRAM at 0xC000_0000 */
 	tzc400_configure_region(STM32MP1_FILTER_BIT_ALL, 1,
@@ -104,9 +130,7 @@
 				TZC_REGION_ACCESS_RDWR(STM32MP1_TZC_SDMMC_ID));
 
 	/* Raise an exception if a NS device tries to access secure memory */
-	tzc400_set_action(TZC_ACTION_ERR);
-
-	tzc400_enable_filters();
+	init_tzc400_end(TZC_ACTION_ERR);
 }
 
 /*******************************************************************************