diff --git a/drivers/arm/rss/rss_comms_protocol.h b/drivers/arm/rss/rss_comms_protocol.h
new file mode 100644
index 0000000..9a38057
--- /dev/null
+++ b/drivers/arm/rss/rss_comms_protocol.h
@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2022, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ */
+
+#ifndef __RSS_COMMS_PROTOCOL_H__
+#define __RSS_COMMS_PROTOCOL_H__
+
+#include <cdefs.h>
+#include <stdint.h>
+
+#include <psa/client.h>
+#include "rss_comms_protocol_embed.h"
+#include "rss_comms_protocol_pointer_access.h"
+
+enum rss_comms_protocol_version_t {
+	RSS_COMMS_PROTOCOL_EMBED = 0,
+	RSS_COMMS_PROTOCOL_POINTER_ACCESS = 1,
+};
+
+struct __packed serialized_rss_comms_header_t {
+	uint8_t protocol_ver;
+	uint8_t seq_num;
+	uint16_t client_id;
+};
+
+/* MHU message passed from Host to RSS to deliver a PSA client call */
+struct __packed serialized_rss_comms_msg_t {
+	struct serialized_rss_comms_header_t header;
+	union __packed {
+		struct rss_embed_msg_t embed;
+		struct rss_pointer_access_msg_t pointer_access;
+	} msg;
+};
+
+/* MHU reply message to hold the PSA client reply result returned by RSS */
+struct __packed serialized_rss_comms_reply_t {
+	struct serialized_rss_comms_header_t header;
+	union __packed {
+		struct rss_embed_reply_t embed;
+		struct rss_pointer_access_reply_t pointer_access;
+	} reply;
+};
+
+/* in_len and out_len are uint8_ts, therefore if there are more than 255 iovecs
+ * an error may occur.
+ */
+CASSERT(PSA_MAX_IOVEC <= UINT8_MAX, assert_rss_comms_max_iovec_too_large);
+
+psa_status_t rss_protocol_serialize_msg(psa_handle_t handle,
+					int16_t type,
+					const psa_invec *in_vec,
+					uint8_t in_len,
+					const psa_outvec *out_vec,
+					uint8_t out_len,
+					struct serialized_rss_comms_msg_t *msg,
+					size_t *msg_len);
+
+psa_status_t rss_protocol_deserialize_reply(psa_outvec *out_vec,
+					    uint8_t out_len,
+					    psa_status_t *return_val,
+					    const struct serialized_rss_comms_reply_t *reply,
+					    size_t reply_size);
+
+#endif /* __RSS_COMMS_PROTOCOL_H__ */