sysbuild: support sample configuration of extra images

This commit introduces the possibility of a sample to locate
configuration files for extra images that are used when building with
MCUboot.

This allows use-cases where a sample, A, want to include MCUboot but has
adjustments to the default MCUboot configuration.

By adding a Kconfig fragment `<sample>/sysbuild/mcuboot.conf`, then that
fragment will be used together with the default configuration for
MCUboot.

It is also possible to completely replace the MCUboot configuration.
This is done by creating `<sample>/sysbuild/mcuboot/` folder.
This folder will then be used as the `APPLICATION_CONFIG_DIR` when
building MCUboot.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>

cmake/modules/configuration_files.cmake

@@ -24,6 +24,7 @@ include_guard(GLOBAL)
 
 include(extensions)
 
+zephyr_get(APPLICATION_CONFIG_DIR)
 if(DEFINED APPLICATION_CONFIG_DIR)
   string(CONFIGURE ${APPLICATION_CONFIG_DIR} APPLICATION_CONFIG_DIR)
   if(NOT IS_ABSOLUTE ${APPLICATION_CONFIG_DIR})

doc/build/sysbuild/index.rst

@@ -484,6 +484,69 @@ disable it using the Kconfig option ``SECOND_SAMPLE``.
 For more information on setting sysbuild Kconfig options,
 see :ref:`sysbuild_kconfig_namespacing`.
 
+Zephyr application configuration
+================================
+
+When adding a Zephyr application to sysbuild, such as MCUboot, then the
+configuration files from the application (MCUboot) itself will be used.
+
+When integrating multiple applications with each other, then it is often
+necessary to make adjustments to the configuration of extra images.
+
+Sysbuild gives users the ability of creating Kconfig fragments or devicetree
+overlays that will be used together with the application's default configuration.
+Sysbuild also allows users to change :ref:`application-configuration-directory`
+in order to give users full control of an image's configuration.
+
+Zephyr application Kconfig fragment and devicetree overlay
+----------------------------------------------------------
+
+In the folder of the main application, create a Kconfig fragment or a devicetree
+overlay under a sysbuild folder, where the name of the file is
+:file:`<image>.conf` or :file:`<image>.overlay`, for example if your main
+application includes ``my_sample`` then create a :file:`sysbuild/my_sample.conf`
+file or a devicetree overlay :file:`sysbuild/my_sample.overlay`.
+
+A Kconfig fragment could look as:
+
+.. code-block:: none
+
+   # sysbuild/my_sample.conf
+   CONFIG_FOO=n
+
+Zephyr application configuration directory
+------------------------------------------
+
+In the folder of the main application, create a new folder under
+:file:`sysbuild/<image>/`.
+This folder will then be used as ``APPLICATION_CONFIG_DIR`` when building
+``<image>``.
+As an example, if your main application includes ``my_sample`` then create a
+:file:`sysbuild/my_sample/` folder and place any configuration files in
+there as you would normally do:
+
+.. code-block:: none
+
+   <home>/application
+   ├── CMakeLists.txt
+   ├── prj.conf
+   └── sysbuild
+       └── my_sample
+           ├── prj.conf
+           ├── app.overlay
+           └── boards
+               ├── <board_A>.conf
+               ├── <board_A>.overlay
+               ├── <board_B>.conf
+               └── <board_B>.overlay
+
+All configuration files under the :file:`sysbuild/my_sample/` folder will now
+be used when ``my_sample`` is included in the build, and the default
+configuration files for ``my_sample`` will be ignored.
+
+This give you full control on how images are configured when integrating those
+with ``application``.
+
 Adding non-Zephyr applications to sysbuild
 ******************************************
 

share/sysbuild/cmake/modules/sysbuild_extensions.cmake

@@ -117,6 +117,39 @@ function(ExternalZephyrProject_Add)
     )
   endif()
 
+  set(sysbuild_image_conf_dir ${APP_DIR}/sysbuild)
+  set(sysbuild_image_name_conf_dir ${APP_DIR}/sysbuild/${ZBUILD_APPLICATION})
+  # User defined `-D<image>_CONF_FILE=<file.conf>` takes precedence over anything else.
+  if (NOT ${ZBUILD_APPLICATION}_CONF_FILE)
+    if(EXISTS ${sysbuild_image_name_conf_dir})
+      set(${ZBUILD_APPLICATION}_APPLICATION_CONFIG_DIR ${sysbuild_image_name_conf_dir}
+          CACHE INTERNAL "Application configuration dir controlled by sysbuild"
+      )
+    endif()
+
+     # Check for sysbuild related configuration fragments.
+     # The contents of these are appended to the image existing configuration
+     # when user is not specifying custom fragments.
+    if(NOT "${CONF_FILE_BUILD_TYPE}" STREQUAL "")
+      set(sysbuil_image_conf_fragment ${sysbuild_image_conf_dir}/${ZBUILD_APPLICATION}_${CONF_FILE_BUILD_TYPE}.conf)
+    else()
+      set(sysbuild_image_conf_fragment ${sysbuild_image_conf_dir}/${ZBUILD_APPLICATION}.conf)
+    endif()
+
+    if (NOT ${ZBUILD_APPLICATION}_OVERLAY_CONFIG AND EXISTS ${sysbuild_image_conf_fragment})
+      set(${ZBUILD_APPLICATION}_OVERLAY_CONFIG ${sysbuild_image_conf_fragment}
+          CACHE INTERNAL "Kconfig fragment defined by main application"
+      )
+    endif()
+
+    # Check for overlay named <ZBUILD_APPLICATION>.overlay.
+    set(sysbuild_image_dts_overlay ${sysbuild_image_conf_dir}/${ZBUILD_APPLICATION}.overlay)
+    if (NOT ${ZBUILD_APPLICATION}_DTC_OVERLAY_FILE AND EXISTS ${sysbuild_image_dts_overlay})
+      set(${ZBUILD_APPLICATION}_DTC_OVERLAY_FILE ${sysbuild_image_dts_overlay}
+          CACHE INTERNAL "devicetree overlay file defined by main application"
+      )
+    endif()
+  endif()
   # CMake variables which must be known by all Zephyr CMake build systems
   # Those are settings which controls the build and must be known to CMake at
   # invocation time, and thus cannot be passed though the sysbuild cache file.