samples: bluetooth: mesh: add external flash for dfu target

Commit adds ability to build dfu target sample to use
external flash as the secondary partiiotn for dfu procedure.
The ability was added only for nrf52840 DK.

Signed-off-by: Aleksandr Khromykh <[email protected]>

Author: alxelax

samples/bluetooth/mesh/dfu/target/README.rst

@@ -202,6 +202,25 @@ In this sample, UART and SEGGER RTT are available as logging backends.
 .. note::
    With the :zephyr:board:`nrf52840dongle`, only logging over UART is available.
 
+External flash support
+======================
+
+This sample supports external flash memory as secondary storage partition for saving of the incoming firmware images.
+See :ref:`ug_bootloader_external_flash` for more information on external flash support as a partition in the :ref:`ug_bootloader_mcuboot_nsib`.
+The default configuration does not support external flash memory.
+To enable external flash support, set :makevar:`FILE_SUFFIX` to ``ext_flash`` when building the sample.
+
+Build the sample using the following command:
+
+.. code-block:: console
+
+   west build -p -b *board_name* -- -DFILE_SUFFIX=ext_flash
+
+.. note::
+   The external flash is not erased during the internal flash erasing procedure.
+   See `nRF Util`_ for more information on how to erase the external flash.
+   Currently, only the external flash on the ``nrf52840dk/nrf52840`` board is supported at the moment.
+
 Dependencies
 ************
 

samples/bluetooth/mesh/dfu/target/sample.yaml

@@ -18,3 +18,15 @@ tests:
       - bluetooth
       - ci_build
       - sysbuild
+  sample.bluetooth.mesh_dfu_target.ext_flash:
+    sysbuild: true
+    build_only: true
+    integration_platforms:
+      - nrf52840dk/nrf52840
+    platform_allow:
+      - nrf52840dk/nrf52840
+    extra_args: FILE_SUFFIX=ext_flash
+    tags:
+      - bluetooth
+      - ci_build
+      - sysbuild

samples/bluetooth/mesh/dfu/target/sysbuild/mcuboot_ext_flash.conf

@@ -0,0 +1,13 @@
+#
+# Copyright (c) 2025 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+#
+################################################################################
+
+CONFIG_NORDIC_QSPI_NOR=y
+CONFIG_NORDIC_QSPI_NOR_FLASH_LAYOUT_PAGE_SIZE=4096
+CONFIG_NORDIC_QSPI_NOR_STACK_WRITE_BUFFER_SIZE=16
+
+# Maximum number of sectors that image can have
+CONFIG_BOOT_MAX_IMG_SECTORS=256

samples/bluetooth/mesh/dfu/target/sysbuild/mcuboot_ext_flash.overlay

@@ -0,0 +1,11 @@
+/* Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+ */
+
+/ {
+	chosen {
+		zephyr,code-partition = &boot_partition;
+		nordic,pm-ext-flash = &mx25r64;
+	};
+};

samples/bluetooth/mesh/dfu/target/sysbuild/target_ext_flash.overlay

@@ -0,0 +1,10 @@
+/* Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+ */
+
+/ {
+	chosen {
+		nordic,pm-ext-flash = &mx25r64;
+	};
+};

samples/bluetooth/mesh/dfu/target/sysbuild_ext_flash.conf

@@ -0,0 +1,11 @@
+#
+# Copyright (c) 2025 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+#
+
+SB_CONFIG_BOOTLOADER_MCUBOOT=y
+SB_CONFIG_PM_EXTERNAL_FLASH_MCUBOOT_SECONDARY=y
+SB_CONFIG_DFU_ZIP=y
+SB_CONFIG_DFU_ZIP_BLUETOOTH_MESH_METADATA=y
+SB_CONFIG_DFU_ZIP_BLUETOOTH_MESH_METADATA_FWID_MCUBOOT_VERSION=y