arm: core: mpu: Add ARM MPU support

This patch adds an initial driver for the ARM MPU.
This driver has been tested on ARM Beetle and STM32F4.

Change-Id: I2bc4031961ec5a1d569929249237646f4a349f16
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@linaro.org>

arch/arm/core/Kconfig

@@ -96,3 +96,7 @@ endmenu
 if CPU_CORTEX_M
 source "arch/arm/core/cortex_m/Kconfig"
 endif
+
+if CPU_HAS_MPU
+source "arch/arm/core/cortex_m/mpu/Kconfig"
+endif

arch/arm/core/Makefile

@@ -8,3 +8,4 @@ obj-$(CONFIG_GEN_SW_ISR_TABLE) += isr_wrapper.o
 obj-$(CONFIG_CPLUSPLUS) += __aeabi_atexit.o
 obj-$(CONFIG_IRQ_OFFLOAD) += irq_offload.o
 obj-$(CONFIG_CPU_CORTEX_M) += cortex_m/
+obj-$(CONFIG_CPU_HAS_MPU) += cortex_m/mpu/

arch/arm/core/cortex_m/mpu/Kconfig

@@ -0,0 +1,14 @@
+# Kconfig - Memory Protection Unit (MPU) configuration options
+
+#
+# Copyright (c) 2017 Linaro Limited
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+config ARM_MPU
+	bool "ARM MPU Support"
+	depends on CPU_HAS_MPU
+	default n
+	help
+	  MCU has ARM MPU

arch/arm/core/cortex_m/mpu/Makefile

@@ -0,0 +1 @@
+obj-$(CONFIG_ARM_MPU) += arm_mpu.o

arch/arm/core/cortex_m/mpu/arm_mpu.c

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2017 Linaro Limited.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <device.h>
+#include <init.h>
+#include <kernel.h>
+#include <soc.h>
+#include <arch/arm/cortex_m/cmsis.h>
+#include <arch/arm/cortex_m/mpu/arm_mpu.h>
+
+#define ARM_MPU_DEV ((volatile struct arm_mpu *) ARM_MPU_BASE)
+
+static inline u8_t _get_num_regions(void)
+{
+	u32_t type = ARM_MPU_DEV->type;
+
+	type = (type & 0xFF00) >> 8;
+
+	return (u8_t)type;
+}
+
+static void _region_init(u32_t index, u32_t region_addr,
+			 u32_t region_attr)
+{
+	/* Select the region you want to access */
+	ARM_MPU_DEV->rnr = index;
+	/* Configure the region */
+	ARM_MPU_DEV->rbar = region_addr | REGION_VALID | index;
+	ARM_MPU_DEV->rasr = region_attr | REGION_ENABLE;
+}
+
+/*
+ * @brief MPU default configuration
+ *
+ * This function provides the default configuration mechanism for the Memory
+ * Protection Unit (MPU).
+ */
+static void _arm_mpu_config(void)
+{
+	u32_t r_index;
+
+	/* ARM MPU supports up to 16 Regions */
+	if (mpu_config.num_regions > _get_num_regions()) {
+		return;
+	}
+
+	/* Disable MPU */
+	ARM_MPU_DEV->ctrl = 0;
+
+	/* Configure regions */
+	for (r_index = 0; r_index < mpu_config.num_regions; r_index++) {
+		_region_init(r_index,
+			     mpu_config.mpu_regions[r_index].base,
+			     mpu_config.mpu_regions[r_index].attr);
+	}
+
+	/* Enable MPU */
+	ARM_MPU_DEV->ctrl = 1;
+
+	/* Make sure that all the registers are set before proceeding */
+	__DSB();
+	__ISB();
+}
+
+static int arm_mpu_init(struct device *arg)
+{
+	ARG_UNUSED(arg);
+
+	_arm_mpu_config();
+
+	return 0;
+}
+
+SYS_INIT(arm_mpu_init, PRE_KERNEL_1,
+	 CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);