stm32cube: stm32n6: Allow building a chainloaded secure application

When building a chain-loaded secure application, build and call
system_stm32n6_s.c file.
Similarly to what is done on system_stm32n6xx_fsbl.c, remove CMSE_NS_ENTRY
modifier as Secure FW has no entry funcs.

Signed-off-by: Erwan Gouriou <[email protected]>

Author: erwango

stm32cube/stm32n6xx/CMakeLists.txt

@@ -1,8 +1,13 @@
 # Copyright (c) 2025 STMicroelectronics
 #
 # SPDX-License-Identifier: Apache-2.0
-
-zephyr_library_sources(soc/system_stm32n6xx_fsbl.c)
+if(CONFIG_BOOTLOADER_MCUBOOT)
+	zephyr_include_directories(soc)
+	zephyr_include_directories(soc/Templates)
+	zephyr_library_sources(soc/system_stm32n6xx_s.c)
+else()
+	zephyr_library_sources(soc/system_stm32n6xx_fsbl.c)
+endif()
 zephyr_library_sources(drivers/src/stm32n6xx_hal.c)
 zephyr_library_sources(drivers/src/stm32n6xx_hal_rcc.c)
 zephyr_library_sources(drivers/src/stm32n6xx_hal_rcc_ex.c)

stm32cube/stm32n6xx/README

@@ -52,6 +52,7 @@ Patch List:
      which we don't need right now.
     Impacted files:
     -soc/system_stm32n6xx_fsbl.c
+    -soc/system_stm32n6xx_s.c
 
    *Fix SDIO initialization failure when skipping card identification sequence
      Fixes an issue in the STM32HN6 SDIO driver where HAL_SDIO_Init() fails if

stm32cube/stm32n6xx/soc/system_stm32n6xx_s.c

@@ -425,7 +425,7 @@ void SystemCoreClockUpdate(void)
   *         other parameters.
   * @retval SystemCoreClock value
   */
-CMSE_NS_ENTRY uint32_t SECURE_SystemCoreClockUpdate(void)
+uint32_t SECURE_SystemCoreClockUpdate(void)
 {
   SystemCoreClockUpdate();