arch: arm: Cortex-A/R: add pre stack platform init

Adds platform (SoC) specific startup hook executed before the stack is
initialised.

Signed-off-by: Tavish Naruka <[email protected]>

Author: Tavish Naruka

arch/arm/core/Kconfig

@@ -174,6 +174,14 @@ config PLATFORM_SPECIFIC_INIT
 
 	  This option is deprecated, use SOC_RESET_HOOK instead.
 
+config PLATFORM_SPECIFIC_PRE_STACK_INIT
+	bool "Platform (SOC) specific startup hook executed before the stack is initialised"
+	help
+	  The platform specific initialization code (z_arm_platform_pre_stack_init) is
+	  executed in the early startup code right after the registers are set to known
+	  values and before stack is set up. Note that this code cannot use the stack unlike
+	  z_arm_platform_init.
+
 config FAULT_DUMP
 	int "Fault dump level"
 	default 2

arch/arm/core/cortex_a_r/reset.S

@@ -203,6 +203,10 @@ EL1_Reset_Handler:
 
 #endif /* CONFIG_DCLS */
 
+#if defined(CONFIG_PLATFORM_SPECIFIC_PRE_STACK_INIT)
+    bl z_arm_platform_pre_stack_init
+#endif
+
 #if defined(CONFIG_CPU_CORTEX_R52_CACHE_SEGREGATION)
     ldr r0, =IMP_CSCTLR(CONFIG_CPU_CORTEX_R52_ICACHE_FLASH_WAY,
                         CONFIG_CPU_CORTEX_R52_DCACHE_FLASH_WAY)