[nrf fromlist] boot: zephyr: Clean up before chainloading by default

This changes the default mcuboot configuration for zephyr
applications to clean up before booting the user application. The
reason for this change is that mcuboot may configure protection (e.g.
MPU stack guard) which is then used by the user application during
its startup code prior to cleaning the configuration up, this can
lead to a unbootable application and potentially irrecoverable
module, therefore cleaning up is now being enabled by default.

Upstream PR: mcu-tools/mcuboot#1635

Signed-off-by: Jamie McCrae <[email protected]>

boot/zephyr/Kconfig

@@ -148,20 +148,18 @@ config BOOT_SIGNATURE_KEY_FILE
 config MCUBOOT_CLEANUP_ARM_CORE
 	bool "Perform core cleanup before chain-load the application"
 	depends on CPU_CORTEX_M
-	default y if !ARCH_SUPPORTS_ARCH_HW_INIT
+	default y
 	help
 	  This option instructs MCUboot to perform a clean-up of a set of
 	  architecture core HW registers before junping to the application
 	  firmware. The clean-up sets these registers to their warm-reset
 	  values as specified by the architecture.
 
-	  By default, this option is enabled only if the architecture does
-	  not have the functionality to perform such a register clean-up
-	  during application firmware boot.
-
-	  Zephyr applications on Cortex-M will perform this register clean-up
-	  by default, if they are chain-loadable by MCUboot, so MCUboot does
-	  not need to perform such a cleanup itself.
+	  This option is enabled by default to prevent possible problems when
+	  booting zephyr (or other) applications whereby e.g. a MPU stack guard
+	  may be initialised in RAM which is then used by the application
+	  start-up code which can cause a module fault and potentially make the
+	  module irrecoverable.
 
 config MBEDTLS_CFG_FILE
 	default "mcuboot-mbedtls-cfg.h"