diff --git a/kernel/ethosu_mailbox.h b/kernel/ethosu_mailbox.h
index c192b54..ea4409f 100644
--- a/kernel/ethosu_mailbox.h
+++ b/kernel/ethosu_mailbox.h
@@ -50,6 +50,14 @@
 	struct idr            msg_idr;
 };
 
+/**
+ * struct ethosu_mailbox_msg - Mailbox message
+ * @id: Message id
+ * @type: Message request type
+ * @fail: Message failure callback
+ *
+ * The fail callback will be called with the device mutex locked
+ */
 struct ethosu_mailbox_msg {
 	int      id;
 	uint32_t type;
@@ -77,6 +85,8 @@
 /**
  * ethosu_mailbox_register() - Register the ethosu_mailbox_msg in ethosu_mailbox
  *
+ * Context: Must be called with the device mutex locked
+ *
  * Return: 0 on success, else error code.
  */
 int ethosu_mailbox_register(struct ethosu_mailbox *mbox,
@@ -84,6 +94,8 @@
 
 /**
  * ethosu_mailbox_free_id() - Free the id of the ethosu_mailbox_msg
+ *
+ * Context: Must be called with the device mutex locked
  */
 void ethosu_mailbox_deregister(struct ethosu_mailbox *mbox,
 			       struct ethosu_mailbox_msg *msg);
@@ -91,6 +103,8 @@
 /**
  * ethosu_mailbox_find() - Find mailbox message
  *
+ * Context: Must be called with the device mutex locked
+ *
  * Return: a valid pointer on success, otherwise an error ptr.
  */
 struct ethosu_mailbox_msg *ethosu_mailbox_find(struct ethosu_mailbox *mbox,
@@ -101,6 +115,8 @@
  * ethosu_mailbox_fail() - Fail mailbox messages
  *
  * Call fail() callback on all messages in pending list.
+ *
+ * Context: Must be called with the device mutex locked
  */
 void ethosu_mailbox_fail(struct ethosu_mailbox *mbox);