arch/arm: introduce the pre-stack/RAM init hook

Introduce hook for customize reset.S code even before stack is
initialized or RAM is accessed. Hook can be enabled using
CONFIG_ARM_SOC_START_HOOK=y.
Hook implementation is by soc_start_hook() function which should
be provided by custom code.

Signed-off-by: Andrzej Puzdrowski <[email protected]>

Author: nvlsianpu

arch/arm/Kconfig

@@ -144,6 +144,13 @@ config ARM_ON_EXIT_CPU_IDLE
 	  observed on some SoCs caused by a memory access following WFI/WFE
 	  instructions.
 
+config SOC_PRE_RAM_HOOK
+	bool "include cpu start hook"
+	depends on CPU_CORTEX_M
+	help
+	  This hooks run almost after startup - even before any stack is initiated
+	  or RAM is accessed.
+
 rsource "core/Kconfig"
 rsource "core/Kconfig.vfp"
 

arch/arm/core/cortex_m/reset.S

@@ -35,6 +35,10 @@ GTEXT(z_arm_init_arch_hw_at_boot)
 #if defined(CONFIG_PM_S2RAM)
 GTEXT(arch_pm_s2ram_resume)
 #endif
+#if defined(CONFIG_SOC_PRE_RAM_HOOK)
+GTEXT(soc_pre_ram_hook)
+#endif
+
 
 /*
  * PACBTI Mask for CONTROL register:
@@ -100,6 +104,10 @@ SECTION_SUBSEC_FUNC(TEXT,_reset_section,__start)
 
 #endif /* CONFIG_INIT_ARCH_HW_AT_BOOT */
 
+#if defined(CONFIG_SOC_PRE_RAM_HOOK)
+    /* Call custom code that executes before any stack is set up or RAM memory is accessed */
+    bl soc_pre_ram_hook
+#endif
 #if defined(CONFIG_PM_S2RAM)
     /*
      * Temporarily set MSP to interrupt stack so that arch_pm_s2ram_resume can