single_slot: Remove default overlay

The default overlay for FW loader sets code-partition to
slot1_partition, which stays with direct conflict with the merged slot
approach:
 - slot1_partition must point to the merged partition to allow SMP logic
   to parse the FW loader magic & version
 - if FW loader indeed uses slot1_partition with ROM_START_OFFSET, than
   it is impossible to correctly boot the radio core FW, since it cannot
   use the same value of the ROM_START_OFFSET (2kB NVM waste) and there
   is no way to tell the FW loader code in soc.c to boot the radio with
   a different value of ROM_START_OFFSET.
 - the size of the code-partition must be different from the size of the
   partition parsed by the SMP, so there is a protection against
   potential code partition overflow and the flash area API can reach
   past the code partition area.

One solution would be to change the contents of the
FIRMWARE_LOADER_image_default.overlay, but since it would force every
user of the FW loader within Zephyr to add a new partition alias, it is
far less intrusive to remove this overlay from sysbuild.cmake script in
those samples, that use merged slot approach.

Ref: NCSDK-36779

Signed-off-by: Tomasz Chyrowicz <[email protected]>

Author: tomchy

samples/dfu/single_slot/sysbuild.cmake

@@ -0,0 +1,21 @@
+#
+# Copyright (c) 2025 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+#
+
+cmake_minimum_required(VERSION 3.20.0)
+if (SB_CONFIG_MCUBOOT_SIGN_MERGED_BINARY)
+  # If firmware loader images are merged, there is a necessity to use a different code-partition
+  # than the slot1_partition, enforced by the FIRMWARE_LOADER_image_default.overlay, configured
+  # through EXTRA_DTC_OVERLAY_FILE cache variable.
+  # In the merged slot approach the slot1_partition should be defined as the merged partition and
+  # code-partition should point to a subpartition of the slot1_partition.
+  # The code-partition is configured in the image-specific overlay files.
+  FirmwareUpdaterImage_Get(fw_loader_images)
+  foreach(image IN LISTS fw_loader_images)
+    # Remove the default overlay file.
+    set(${image}_EXTRA_DTC_OVERLAY_FILE "" CACHE INTERNAL "Application extra DTC overlay file"
+      FORCE)
+  endforeach()
+endif()

samples/dfu/single_slot/sysbuild/ble_mcumgr/boards/nrf54h20dk_nrf54h20_cpuapp.overlay

@@ -6,8 +6,8 @@
 
 #include "../../nrf54h20.overlay"
 
-/* The zephyr,code-partition is always set to fw_loader_partition in firmware
- * loader image(s).
- */
-/delete-node/ &slot1_partition;
-slot1_partition: &fw_loader_partition {};
+/ {
+	chosen {
+		zephyr,code-partition = &fw_loader_partition;
+	};
+};

samples/dfu/single_slot/sysbuild/fw_loader_ipc_radio.overlay

@@ -6,8 +6,8 @@
 
 #include "nrf54h20.overlay"
 
-/* The zephyr,code-partition is always set to fw_loader_partition in firmware
- * loader image(s).
- */
-/delete-node/ &slot1_partition;
-slot1_partition: &cpurad_slot0_partition {};
+/ {
+	chosen {
+		zephyr,code-partition = &cpurad_slot0_partition;
+	};
+};