retention: Add boot mode system

Adds a boot mode system which allows for redirecting the boot
target of a device depending upon the state of a retained value.

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

include/zephyr/retention/bootmode.h

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2023 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @file
+ * @brief Public API for boot mode interface
+ */
+
+#ifndef ZEPHYR_INCLUDE_RETENTION_BOOTMODE_
+#define ZEPHYR_INCLUDE_RETENTION_BOOTMODE_
+
+#include <stdint.h>
+#include <stddef.h>
+#include <zephyr/kernel.h>
+#include <zephyr/device.h>
+#include <zephyr/types.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Boot mode interface
+ * @defgroup boot_mode_interface Boot mode interface
+ * @ingroup retention
+ * @{
+ */
+
+enum BOOT_MODE_TYPES {
+	/** Default (normal) boot, to user application */
+	BOOT_MODE_TYPE_NORMAL = 0x00,
+
+	/** Bootloader boot mode (e.g. serial recovery for MCUboot) */
+	BOOT_MODE_TYPE_BOOTLOADER,
+};
+
+/**
+ * @brief		Checks if the boot mode of the device is set to a specific value.
+ *
+ * @param boot_mode	Expected boot mode to check.
+ *
+ * @retval 1		If successful and boot mode matches.
+ * @retval 0		If boot mode does not match.
+ * @retval -errno	Error code code.
+ */
+int bootmode_check(uint8_t boot_mode);
+
+/**
+ * @brief		Sets boot mode of device.
+ *
+ * @param boot_mode	Boot mode value to set.
+ *
+ * @retval 0		If successful.
+ * @retval -errno	Error code code.
+ */
+int bootmode_set(uint8_t boot_mode);
+
+/**
+ * @brief		Clear boot mode value (sets to 0) - which corresponds to
+ *			#BOOT_MODE_TYPE_NORMAL.
+ *
+ * @retval 0		If successful.
+ * @retval -errno	Error code code.
+ */
+int bootmode_clear(void);
+
+/**
+ * @}
+ */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ZEPHYR_INCLUDE_RETENTION_BOOTMODE_ */

subsys/retention/CMakeLists.txt

@@ -2,3 +2,4 @@
 
 zephyr_library()
 zephyr_library_sources(retention.c)
+zephyr_library_sources_ifdef(CONFIG_RETENTION_BOOT_MODE bootmode.c)

subsys/retention/Kconfig

@@ -5,10 +5,10 @@ menuconfig RETENTION
 	bool "Retention support"
 	depends on CRC
 	depends on RETAINED_MEM
-	depends on DT_HAS_ZEPHYR_DATA_RETENTION_ENABLED
+	depends on DT_HAS_ZEPHYR_RETENTION_ENABLED
 	help
-	  Enables support for the data retention system, which uses retained
-	  memory drivers.
+	  Enables support for the retention system, which uses retained memory
+	  drivers.
 
 if RETENTION
 
@@ -16,8 +16,8 @@ config RETENTION_INIT_PRIORITY
 	int "Retention devices init priority"
 	default 86
 	help
-	  Data retention devices initialization priority (must be higher than
-	  init priorities for retained memory drivers.
+	  Retention device initialization priority (must be higher than init
+	  priorities for retained memory drivers.
 
 config RETENTION_BUFFER_SIZE
 	int "Retention stack buffer sizes"
@@ -27,6 +27,22 @@ config RETENTION_BUFFER_SIZE
 	  Size of buffers (stack based) used when reading and writing data
 	  from/to the retention device.
 
+menu "Retention modules"
+
+config RETENTION_BOOT_MODE
+	bool "Boot mode"
+	help
+	  Adds a boot mode system that allows for changing execution flow
+	  depending upon the value of a boot mode parameter. Can be used for
+	  e.g. button-less bootloader serial recovery mode entering from the
+	  application.
+
+	  In order to use this, a retention area with at least 1 usable user
+	  byte must be created and set as the "zephyr,boot-mode" chosen node
+	  via device tree.
+
+endmenu
+
 module = RETENTION
 module-str = retention
 source "subsys/logging/Kconfig.template.log_config"

subsys/retention/bootmode.c

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2023, Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/kernel.h>
+#include <zephyr/devicetree.h>
+#include <zephyr/retention/retention.h>
+#include <zephyr/logging/log.h>
+
+LOG_MODULE_REGISTER(bootmode, CONFIG_RETENTION_LOG_LEVEL);
+
+static const struct device *boot_mode_dev = DEVICE_DT_GET(DT_CHOSEN(zephyr_boot_mode));
+
+int bootmode_check(uint8_t boot_mode)
+{
+	int rc;
+
+	rc = retention_is_valid(boot_mode_dev);
+
+	if (rc == 1) {
+		uint8_t stored_mode;
+
+		rc = retention_read(boot_mode_dev, 0, &stored_mode, sizeof(stored_mode));
+
+		/* Only check if modes match if there was no error, otherwise return the error */
+		if (rc == 0) {
+			if (stored_mode == boot_mode) {
+				rc = 1;
+			}
+		}
+	}
+
+	return rc;
+}
+
+int bootmode_set(uint8_t boot_mode)
+{
+	return retention_write(boot_mode_dev, 0, &boot_mode, sizeof(boot_mode));
+}
+
+int bootmode_clear(void)
+{
+	return retention_clear(boot_mode_dev);
+}