arch: arc: Restore MPU registers to its initial states between tests

EMSK boards can't be reset between tests due to hardware configures.
MPU v3 configs in previous test could cause exceptions in the following
tests. This commit fixes this issue by restoring MPU registers initial
states at early init stage.

Signed-off-by: Yuguo Zou <[email protected]>

Author: YuguoWH

arch/arc/Kconfig

@@ -328,4 +328,10 @@ config ARC_EXCEPTION_DEBUG
 	  and parameters, at a cost of code/data size for the human-readable
 	  strings.
 
+config ARC_CUSTOM_INIT
+	bool "Enable custom initialization code"
+	help
+	  This option enables custom initialization code as a supplement
+	  method of initialization to some corner cases on SoCs and boards.
+
 endmenu

arch/arc/core/reset.S

@@ -121,6 +121,38 @@ invalidate_dcache:
 
 done_cache_invalidate:
 
+/*
+ * ARC Custom Initialization
+ * For scenarios where board hardware is not re-initialized between tests,
+ * some settings need to be restored to its default initial states as a
+ * substitution of normal hardware reset sequence.
+ */
+#if defined(CONFIG_ARC_CUSTOM_INIT)
+	/* Set MPU (v3) registers to default */
+#if CONFIG_ARC_MPU_VER == 3
+	/* Set default reset value to _ARC_V2_MPU_EN register */
+#define ARC_MPU_EN_RESET_VALUE 0x400181C0
+	mov_s r1, ARC_MPU_EN_RESET_VALUE
+	sr r1, [_ARC_V2_MPU_EN]
+	/* Get MPU region numbers */
+	lr r3, [_ARC_V2_MPU_BUILD]
+	lsr_s r3, r3, 8
+	and r3, r3, 0xff
+	mov_s r1, 0
+	mov_s r2, 0
+	/* Set all MPU regions by iterating index */
+mpu_regions_reset:
+	brge r2, r3, done_mpu_regions_reset
+	sr r2, [_ARC_V2_MPU_INDEX]
+	sr r1, [_ARC_V2_MPU_RSTART]
+	sr r1, [_ARC_V2_MPU_REND]
+	sr r1, [_ARC_V2_MPU_RPER]
+	add_s r2, r2, 1
+	b_s mpu_regions_reset
+done_mpu_regions_reset:
+#endif
+#endif
+
 #if defined(CONFIG_SYS_POWER_DEEP_SLEEP_STATES) && \
 	!defined(CONFIG_BOOTLOADER_CONTEXT_RESTORE)
         jl @_sys_resume_from_deep_sleep

boards/arc/em_starterkit/em_starterkit_em7d_defconfig

@@ -20,3 +20,4 @@ CONFIG_GPIO=y
 CONFIG_ARC_MPU_ENABLE=y
 CONFIG_ARC_HAS_SECURE=y
 CONFIG_TRUSTED_EXECUTION_SECURE=y
+CONFIG_ARC_CUSTOM_INIT=y