retention: Add optional mutex disablement

Adds an optional Kconfig to disable use of mutexes in the
retention subsystem.

Signed-off-by: Jamie McCrae <[email protected]>

Author: nordicjm

drivers/retained_mem/Kconfig

@@ -16,7 +16,7 @@ config RETAINED_MEM_INIT_PRIORITY
 	  Retained memory devices initialization priority,
 
 config RETAINED_MEM_MUTEXES
-	int "Retained memory mutex support"
+	bool "Retained memory mutex support"
 	default y
 	depends on MULTITHREADING
 	help

subsys/retention/Kconfig

@@ -19,6 +19,15 @@ config RETENTION_INIT_PRIORITY
 	  Retention device initialization priority (must be higher than init
 	  priorities for retained memory drivers.
 
+config RETENTION_MUTEXES
+	bool "Retention mutex support"
+	default y
+	depends on MULTITHREADING
+	help
+	  Use mutexes to prevent issues with concurrent retention device
+	  access. Should only be disabled whereby retained memory access is
+	  required in an ISR or for special use cases.
+
 config RETENTION_BUFFER_SIZE
 	int "Retention stack buffer sizes"
 	default 16

subsys/retention/retention.c

@@ -31,7 +31,7 @@ enum {
 
 struct retention_data {
 	bool header_written;
-#ifdef CONFIG_MULTITHREADING
+#ifdef CONFIG_RETENTION_MUTEXES
 	struct k_mutex lock;
 #endif
 };
@@ -48,7 +48,7 @@ struct retention_config {
 
 static inline void retention_lock_take(const struct device *dev)
 {
-#ifdef CONFIG_MULTITHREADING
+#ifdef CONFIG_RETENTION_MUTEXES
 	struct retention_data *data = dev->data;
 
 	k_mutex_lock(&data->lock, K_FOREVER);
@@ -59,7 +59,7 @@ static inline void retention_lock_take(const struct device *dev)
 
 static inline void retention_lock_release(const struct device *dev)
 {
-#ifdef CONFIG_MULTITHREADING
+#ifdef CONFIG_RETENTION_MUTEXES
 	struct retention_data *data = dev->data;
 
 	k_mutex_unlock(&data->lock);
@@ -112,7 +112,7 @@ static int retention_checksum(const struct device *dev, uint32_t *output)
 static int retention_init(const struct device *dev)
 {
 	const struct retention_config *config = dev->config;
-#ifdef CONFIG_MULTITHREADING
+#ifdef CONFIG_RETENTION_MUTEXES
 	struct retention_data *data = dev->data;
 #endif
 	ssize_t area_size;
@@ -139,7 +139,7 @@ static int retention_init(const struct device *dev)
 		return -EINVAL;
 	}
 
-#ifdef CONFIG_MULTITHREADING
+#ifdef CONFIG_RETENTION_MUTEXES
 	k_mutex_init(&data->lock);
 #endif