soc: stm32: stm32h7rsx: add MPU region #0 disabling all accesses

Add a first region in the MPU to disable all access to the whole
memory range.  With that ensure that the MPU will block all
access to regions that aren't defined in further regions.
Ensure as well that the peripheral area is accessible.

This handles the errata 2.1.1 PLD might perform linefill to address
that would generate a MemManage Fault of the STM32H7Rxx / STM32H7Sxx
device errate ES0596 - Rev 6.

Signed-off-by: Alain Volmat <[email protected]>

Author: Alain Volmat

soc/st/stm32/stm32h7rsx/CMakeLists.txt

@@ -5,6 +5,8 @@ zephyr_sources(
   soc.c
   )
 
+zephyr_sources(mpu_regions.c)
+
 zephyr_include_directories(.)
 
 set(SOC_LINKER_SCRIPT ${ZEPHYR_BASE}/include/zephyr/arch/arm/cortex_m/scripts/linker.ld CACHE INTERNAL "")

soc/st/stm32/stm32h7rsx/Kconfig

@@ -11,6 +11,7 @@ config SOC_SERIES_STM32H7RSX
 	select HAS_STM32CUBE
 	select CPU_HAS_ARM_MPU
 	select HAS_SWO
+	select CPU_HAS_CUSTOM_FIXED_SOC_MPU_REGIONS
 	select CPU_HAS_FPU_DOUBLE_PRECISION
 	select CPU_HAS_ICACHE
 	select CPU_HAS_DCACHE

soc/st/stm32/stm32h7rsx/mpu_regions.c

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2017 Linaro Limited.
+ * Copyright (c) 2025 STMicroelectronics
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/sys/slist.h>
+#include <zephyr/arch/arm/mpu/arm_mpu.h>
+
+#include <zephyr/arch/arm/cortex_m/arm_mpu_mem_cfg.h>
+
+static const struct arm_mpu_region mpu_regions[] = {
+	/* Use first region to prevent speculative access in entire memory space */
+	/* Region 0 */
+	MPU_REGION_ENTRY("UNMAPPED", 0, {REGION_4G | MPU_RASR_XN_Msk | P_NA_U_NA_Msk}),
+
+	/* Region 1 */
+	MPU_REGION_ENTRY("PERIPH", 0x40000000, REGION_IO_ATTR(REGION_512M)),
+
+#ifdef CONFIG_XIP
+	/* Region 2 */
+	MPU_REGION_ENTRY("FLASH_0", CONFIG_FLASH_BASE_ADDRESS,
+			 REGION_FLASH_ATTR(REGION_FLASH_SIZE)),
+#endif
+
+	/* Region 3 */
+	MPU_REGION_ENTRY("SRAM_0", CONFIG_SRAM_BASE_ADDRESS, REGION_RAM_ATTR(REGION_SRAM_SIZE)),
+};
+
+const struct arm_mpu_config mpu_config = {
+	.num_regions = ARRAY_SIZE(mpu_regions),
+	.mpu_regions = mpu_regions,
+};