applications: nrf_desktop: document the nRF54LM20 DK support

Added documentation for the nrf54lm20dk/nrf54lm20a/cpuapp board target
to the nRF Desktop documentation.

Ref: NCSDK-34043

Signed-off-by: Kamil Piszczek <[email protected]>
(cherry picked from commit afe2432)

Author: kapi-no

applications/nrf_desktop/board_configuration.rst

@@ -166,6 +166,28 @@ Sample mouse or keyboard (``nrf54l15dk/nrf54l15/cpuapp``)
       * The board supports the ``debug`` :ref:`nrf_desktop_bluetooth_guide_fast_pair` configuration that acts as a mouse (``fast_pair`` file suffix).
         The configuration uses the MCUboot bootloader built in the direct-xip mode (``MCUBOOT+XIP``), and supports firmware updates using the :ref:`nrf_desktop_dfu` and :ref:`nrf_desktop_dfu_mcumgr`.
 
+Sample mouse (``nrf54lm20dk/nrf54lm20a/cpuapp``)
+      * The configuration uses the nRF54LM20 Development Kit.
+      * The build types allow to build the application as a mouse.
+      * Inputs are simulated based on the hardware button presses.
+      * Bluetooth LE and USB High-Speed transports are enabled.
+        Bluetooth LE is configured to use Nordic Semiconductor's SoftDevice Link Layer and Low Latency Packet Mode (LLPM).
+        USB High-Speed is configured to use the USB next stack (:kconfig:option:`CONFIG_USB_DEVICE_STACK_NEXT`).
+        The :kconfig:option:`CONFIG_DESKTOP_BLE_ADV_CTRL_ENABLE` and :kconfig:option:`CONFIG_DESKTOP_BLE_ADV_CTRL_SUSPEND_ON_USB` Kconfig options are enabled in mouse configurations to improve the USB High-Speed report rate.
+      * In ``debug`` configurations, logs are provided through the UART.
+        For detailed information on working with the nRF54LM20 DK, see the :ref:`ug_nrf54l15_gs` documentation.
+      * In ``llvm`` configurations, the partition layout is different to accommodate for the higher memory footprint of the ``llvm``  toolchain.
+      * The configurations use the MCUboot bootloader built in the direct-xip mode (``MCUBOOT+XIP``) and support firmware updates using the :ref:`nrf_desktop_dfu`.
+        The application image is verified using a pure ED25519 signature.
+
+      .. note::
+         Currently, the ``nrf54lm20dk/nrf54lm20a/cpuapp`` board target has the following limitations:
+
+         * The software-based cryptography is used in the MCUboot bootloader and application image.
+           The hardware-based cryptography is not yet supported.
+         * The public key that MCUboot uses for validating the application image is stored in the bootloader partition.
+           The hardware Key Management Unit (KMU) is not supported yet.
+
 Sample mouse or dongle (``nrf54h20dk/nrf54h20/cpuapp``)
       * The configuration uses the nRF54H20 Development Kit.
       * The build types allow to build the application as a mouse or dongle.

applications/nrf_desktop/bootloader_dfu.rst

@@ -208,6 +208,9 @@ You can enhance security further by enabling the following sysbuild Kconfig opti
      This option enables generating a default :file:`keyfile.json` file during the build process based on the input file provided by the :kconfig:option:`SB_CONFIG_BOOT_SIGNATURE_KEY_FILE` sysbuild Kconfig option.
      The automatic provisioning is only performed if the west flash command is executed with the ``--erase`` or ``--recover`` flag.
 
+  .. note::
+     KMU is not yet supported for the ``nrf54lm20dk/nrf54lm20a/cpuapp`` board target.
+
 .. _nrf_desktop_bootloader_background_dfu:
 
 Background Device Firmware Upgrade

applications/nrf_desktop/description.rst

@@ -366,7 +366,7 @@ Depending on the development kit you use, you need to select the respective conf
 
       .. table-from-rows:: /includes/sample_board_rows.txt
          :header: heading
-         :rows: nrf52840dk_nrf52840, nrf52833dk_nrf52833, nrf52833dk_nrf52820, nrf5340dk_nrf5340_cpuapp, nrf54l15dk_nrf54l15_cpuapp, nrf54l15dk_nrf54l10_cpuapp, nrf54l15dk_nrf54l05_cpuapp, nrf54h20dk_nrf54h20_cpuapp
+         :rows: nrf52840dk_nrf52840, nrf52833dk_nrf52833, nrf52833dk_nrf52820, nrf5340dk_nrf5340_cpuapp, nrf54l15dk_nrf54l15_cpuapp, nrf54l15dk_nrf54l10_cpuapp, nrf54l15dk_nrf54l05_cpuapp, nrf54lm20dk_nrf54lm20a_cpuapp, nrf54h20dk_nrf54h20_cpuapp
 
       Depending on the configuration, a DK may act either as mouse, keyboard or dongle.
       For information about supported configurations for each board, see the :ref:`nrf_desktop_board_configuration_files` section.
@@ -447,6 +447,10 @@ The application supports the following build types:
      - ``release_4llpmconn``
      - ``nrf52840dongle/nrf52840``
      - Release version of the application with the support for up to four simultaneous Bluetooth LE connections, in Low Latency Packet Mode.
+   * - LLVM
+     - ``llvm``
+     - ``nrf54lm20dk/nrf54lm20a/cpuapp``
+     - Debug version of the application with the support for the ``llvm`` toolchain.
 
 .. note::
     Bootloader-enabled configurations with support for :ref:`serial recovery DFU <nrf_desktop_bootloader_serial_dfu>` or :ref:`background DFU <nrf_desktop_bootloader_background_dfu>` are set as default if they fit in the non-volatile memory.
@@ -1025,6 +1029,9 @@ The private key is used to sign the application image.
 The public key is generated from the private key and is used by MCUboot to validate the application image.
 The public key is securely stored in the Key Management Unit (KMU) hardware peripheral of the nRF54L device.
 
+.. note::
+   KMU is not yet supported for the ``nrf54lm20dk/nrf54lm20a/cpuapp`` board target.
+
 In this application, the application image is automatically signed with a private key by the |NCS| build system.
 The private keys are stored in the application configuration directory of the board.
 Path to the private key is defined by the ``SB_CONFIG_BOOT_SIGNATURE_KEY_FILE`` sysbuild Kconfig option.