boards: nrf9160: use TF-M by default on non-secure builds

By default, when building for the non-secure version of the
board, use TF-M as the secure firmware binary.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>

boards/arm/nrf9160dk_nrf9160/Kconfig.defconfig

@@ -8,6 +8,23 @@ if BOARD_NRF9160DK_NRF9160 || BOARD_NRF9160DK_NRF9160NS
 config BOARD
 	default "nrf9160dk_nrf9160"
 
+# By default, if we build for a Non-Secure version of the board,
+# force building with TF-M as the Secure Execution Environment.
+
+config BUILD_WITH_TFM
+	default y if BOARD_NRF9160DK_NRF9160NS
+
+if BUILD_WITH_TFM
+
+# By default, if we build with TF-M, instruct build system to
+# flash the combined TF-M (Secure) & Zephyr (Non Secure) image
+# (when building in-tree tests).
+config TFM_FLASH_MERGED_BINARY
+	bool
+	default y if TEST_ARM_CORTEX_M
+
+endif # BUILD_WITH_TFM
+
 # For the secure version of the board the firmware is linked at the beginning
 # of the flash, or into the code-partition defined in DT if it is intended to
 # be loaded by MCUboot. If the secure firmware is to be combined with a non-

boards/arm/nrf9160dk_nrf9160/board.cmake

@@ -4,6 +4,10 @@ if(CONFIG_BOARD_NRF9160DK_NRF9160NS)
   set(TFM_PUBLIC_KEY_FORMAT "full")
 endif()
 
+if(CONFIG_TFM_FLASH_MERGED_BINARY)
+  set_property(TARGET runners_yaml_props_target PROPERTY hex_file "${CMAKE_BINARY_DIR}/tfm_merged.hex")
+endif()
+
 board_runner_args(jlink "--device=nRF9160_xxAA" "--speed=4000")
 include(${ZEPHYR_BASE}/boards/common/nrfjprog.board.cmake)
 include(${ZEPHYR_BASE}/boards/common/jlink.board.cmake)

boards/arm/nrf9160dk_nrf9160/nrf9160dk_nrf9160ns.dts

@@ -15,3 +15,8 @@
 		zephyr,code-partition = &slot0_ns_partition;
 	};
 };
+
+/* Disable UART1, because it is used by default in TF-M */
+&uart1 {
+	status = "disabled";
+};