doc: matter: Add documentation for last fabric removal

- Added the page to describe the mechanism and reactions to
the last fabric removal.
- Added instruction on how to implement the custom Fabric Table
delegation.
- Updated the advanced kncofigs pages to describe all possible
reactions to the last fabric removal.

Signed-off-by: Arkadiusz Balys <arkadiusz.balys@nordicsemi.no>

doc/nrf/protocols/matter/end_product/index.rst

@@ -33,3 +33,4 @@ Finally, we discuss topics related to Matter certification (:ref:`ug_matter_devi
    bootloader
    security
    configuring_cd
+   last_fabric_removal_delegate

doc/nrf/protocols/matter/end_product/last_fabric_removal_delegate.rst

@@ -0,0 +1,94 @@
+.. _ug_matter_last_fabric_removal_delegate:
+
+Matter fabric removal
+#####################
+
+.. contents::
+   :local:
+   :depth: 2
+
+.. matter_last_fabric_removal_description_start
+
+When a Matter device is commissioned by the Matter controller, it then belongs to a specific Matter fabric.
+To ensure the interoperability of multiple applications and ecosystems, the device can join the Matter fabrics created by multiple ecosystems using the multi-fabric feature.
+As a result, the device can belong to multiple fabrics and can be managed by multiple Matter controllers.
+
+To remove the device from a fabric, a Matter controller sends the leave request to it and then removes all information collected from the device.
+The device receives the leave request and removes all information about the fabric it is leaving.
+
+.. matter_last_fabric_removal_description_end
+
+Reaction to the last Matter fabric removal
+******************************************
+
+When a device leaves the last Matter fabric it has joined, the network credentials and saved data are no longer usable.
+You can define a reaction to the last fabric removal and decide whether the device should use one of the predefined behaviors, or you can implement custom scenarios.
+
+Predefined last fabric removal behaviors
+========================================
+
+There are four predefined reactions to the last fabric removal available in the :ref:`matter_samples`.
+All behaviors are implemented as a delegation for the Fabric Table module, and the chosen reaction is run as a callback on each fabric removal.
+
+For more information, see the :file:`fabric_table_delegate.h` header file which is located in the Matter samples common directory.
+
+You can choose one of the following reactions to the last fabric removal and instruct the device to:
+
+   * Not react to the last fabric removal and keep the current state of the device.
+   * Remove the network credentials, and keep application-specific non-volatile data.
+   * Remove the network credentials, keep application-specific non-volatile data, and then reboot.
+   * Remove all stored non-volatile data (both network credentials and application-specific data) and reboot.
+   * Remove the network credentials, keep application-specific non-volatile data, and start advertising Bluetooth LE Matter service.
+
+To read more about the reactions to the last fabric and learn how to set the related Kconfigs, see the :ref:`ug_matter_device_advanced_kconfigs` page.
+
+Custom last fabric removal delegate
+===================================
+
+In some cases, the predefined reactions to the last fabric removal are not enough.
+For example, only one of the predefined scenarios includes removing application-specific non-volatile data, but it also requires rebooting the device.
+If the predefined reactions do not meet your requirements, you can define a custom reaction to the last fabric removal.
+
+To implement a custom reaction you need to define a new delegation for the Fabric Table module.
+The Fabric Table module is defined in the Matter stack and is responsible for managing the Matter fabrics to which the device belongs.
+The module stores a list of the delegations and each registered one will be called when the device leaves a Matter fabric.
+You can define multiple delegations, but you need to disable the predefined one.
+
+Disabling the predefined reaction
+---------------------------------
+
+To disable the predefined reaction to the last fabric removal, set the :kconfig:option:`CONFIG_CHIP_LAST_FABRIC_REMOVED_NONE` Kconfig option to ``y``.
+
+Implementing the custom Fabric Table delegation
+-----------------------------------------------
+
+To implement the custom Fabric Table delegation, complete the following points:
+
+   * Include the :file:`app/util/attribute-storage.h` file from the Matter stack core.
+
+      .. code-block:: c
+
+         #include <app/util/attribute-storage.h>
+
+   * Implement a class that inherits ``chip::FabricTable::Delegate`` and contains an overridden ``OnFabricRemoved`` method from the base class.
+
+      .. code-block:: c
+
+         class AppFabricTableDelegate : public chip::FabricTable::Delegate {
+
+            private:
+
+               void OnFabricRemoved(const chip::FabricTable &fabricTable, chip::FabricIndex fabricIndex) {}
+
+         };
+
+   * Implement a reaction on the last fabric removal within the body of the ``OnFabricRemoved`` method.
+   * Call the ``chip::Server::GetInstance().GetFabricTable().AddFabricDelegate`` method of the Fabric Table module in the ``AppTask.Init`` method, and provide the newly created class of delegation as an argument.
+     The new delegation will be added to the delegation table and allows you to call the overridden ``OnFabricRemoved`` method when the last fabric is going to be removed.
+
+.. note::
+   Not all actions implemented in the ``OnFabricRemoved`` can be called directly from the method body, and should be delegated to be done in Zephyr thread of Matter.
+   This is because the device needs to confirm the removal of the fabric and send the acknowledgment to the Matter controller.
+   To delegate actions to the Zephyr thread of Matter, use the ``chip::DeviceLayer::PlatformMgr().ScheduleWork`` method.
+
+To see an example implementation of the Fabric Table delegation, see the :file:`fabric_table_delegate.h` file which is located in the Matter samples common directory.

doc/nrf/protocols/matter/getting_started/advanced_kconfigs.rst

@@ -102,3 +102,31 @@ To read more about the FFS technology and its compatibility with Matter, see the
 
 * `Matter Simple Setup for Wi-Fi Overview`_
 * `Matter Simple Setup for Thread Overview`_
+
+Reaction to the last Matter fabric removal
+==========================================
+
+.. include:: ../end_product/last_fabric_removal_delegate.rst
+    :start-after: matter_last_fabric_removal_description_start
+    :end-before: matter_last_fabric_removal_description_end
+
+When the device leaves the last fabric, one of several reactions can be set to happen.
+
+To enable one of the reactions to the last fabric removal, set the corresponding Kconfig option to ``y``:
+
+* :kconfig:option:`CONFIG_CHIP_LAST_FABRIC_REMOVED_NONE` - Do not react to the last fabric removal.
+  The device will keep all saved data and network credentials, and will not reboot.
+* :kconfig:option:`CONFIG_CHIP_LAST_FABRIC_REMOVED_ERASE_ONLY` - Remove all saved network credentials.
+  The device will remove all saved network credentials, keep application-specific non-volatile data, and will not reboot.
+* :kconfig:option:`CONFIG_CHIP_LAST_FABRIC_REMOVED_ERASE_AND_PAIRING_START` - Remove all saved network credentials and start Bluetooth LE advertising.
+  The device will remove all saved network credentials, keep application-specific non-volatile data, and start advertising Bluetooth LE Matter service.
+  After that, it will be ready for commissioning to Matter over Bluetooth LE.
+* :kconfig:option:`CONFIG_CHIP_LAST_FABRIC_REMOVED_ERASE_AND_REBOOT` - Remove all saved network credentials and reboot the device.
+  This option is selected by default.
+
+  When the :kconfig:option:`CONFIG_CHIP_FACTORY_RESET_ERASE_NVS` Kconfig option is also set to ``y``, the device will also remove all non-volatile data stored on the device, including application-specific entries.
+  This means the device is restored to the factory settings.
+
+.. note::
+  The :kconfig:option:`CONFIG_CHIP_FACTORY_RESET_ERASE_NVS` Kconfig option is set to ``y`` by default.
+  To disable removing application-specific non-volatile data when the :kconfig:option:`CONFIG_CHIP_LAST_FABRIC_REMOVED_ERASE_AND_REBOOT` Kconfig option is selected, set the :kconfig:option:`CONFIG_CHIP_FACTORY_RESET_ERASE_NVS` Kconfig option to ``n``.