diff --git a/drivers/arm/rss/rss_comms.c b/drivers/arm/rss/rss_comms.c
new file mode 100644
index 0000000..28a4925
--- /dev/null
+++ b/drivers/arm/rss/rss_comms.c
@@ -0,0 +1,225 @@
+/*
+ * Copyright (c) 2022, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#include <common/debug.h>
+#include <drivers/arm/mhu.h>
+#include <drivers/arm/rss_comms.h>
+#include <initial_attestation.h>
+#include <psa/client.h>
+
+#include <platform_def.h>
+
+#define TYPE_OFFSET	U(16)
+#define TYPE_MASK	(0xFFFFUL << TYPE_OFFSET)
+#define IN_LEN_OFFSET	U(8)
+#define IN_LEN_MASK	(0xFFUL << IN_LEN_OFFSET)
+#define OUT_LEN_OFFSET	U(0)
+#define OUT_LEN_MASK	(0xFFUL << OUT_LEN_OFFSET)
+
+#define PARAM_PACK(type, in_len, out_len)			  \
+	(((((uint32_t)type) << TYPE_OFFSET) & TYPE_MASK)	| \
+	 ((((uint32_t)in_len) << IN_LEN_OFFSET) & IN_LEN_MASK)	| \
+	 ((((uint32_t)out_len) << OUT_LEN_OFFSET) & OUT_LEN_MASK))
+
+#define PARAM_UNPACK_IN_LEN(ctrl_param) \
+	((size_t)(((ctrl_param) & IN_LEN_MASK) >> IN_LEN_OFFSET))
+
+/* Message types */
+struct __packed packed_psa_call_t {
+	uint8_t protocol_ver;
+	uint8_t seq_num;
+	uint16_t client_id;
+	psa_handle_t handle;
+	uint32_t ctrl_param; /* type, in_len, out_len */
+	uint16_t io_size[4];
+};
+
+struct __packed packed_psa_reply_t {
+	uint8_t protocol_ver;
+	uint8_t seq_num;
+	uint16_t client_id;
+	int32_t return_val;
+	uint16_t out_size[4];
+};
+
+/*
+ * In the current implementation the RoT Service request that requires the
+ * biggest message buffer is the RSS_ATTEST_GET_TOKEN. The maximum required
+ * buffer size is calculated based on the platform-specific needs of
+ * this request.
+ */
+#define MAX_REQUEST_PAYLOAD_SIZE	(PSA_INITIAL_ATTEST_CHALLENGE_SIZE_64 \
+					 + PLAT_ATTEST_TOKEN_MAX_SIZE)
+
+/* Buffer to store the messages to be sent/received. */
+static uint8_t message_buf[MAX_REQUEST_PAYLOAD_SIZE] __aligned(4);
+
+static int32_t pack_params(const psa_invec *invecs,
+			   size_t in_len,
+			   uint8_t *buf,
+			   size_t *buf_len)
+{
+	uint32_t i;
+	size_t payload_size = 0U;
+
+	for (i = 0U; i < in_len; ++i) {
+		if (invecs[i].len > *buf_len - payload_size) {
+			return -1;
+		}
+		memcpy(buf + payload_size, invecs[i].base, invecs[i].len);
+		payload_size += invecs[i].len;
+	}
+
+	*buf_len = payload_size;
+	return 0;
+}
+
+static int serialise_message(const struct packed_psa_call_t *msg,
+			     const psa_invec *invecs,
+			     uint8_t *payload_buf,
+			     size_t *payload_len)
+{
+	size_t message_len = 0U;
+	size_t len;
+
+	/* Copy the message header into the payload buffer. */
+	len = sizeof(*msg);
+	if (len > *payload_len) {
+		ERROR("[RSS-COMMS] Message buffer too small.\n");
+		return -1;
+	}
+	memcpy(payload_buf, (const void *)msg, len);
+	message_len += len;
+
+	/* The input data will follow the message header in the payload buffer. */
+	len = *payload_len - message_len;
+	if (pack_params(invecs, PARAM_UNPACK_IN_LEN(msg->ctrl_param),
+			payload_buf + message_len, &len) != 0) {
+		ERROR("[RSS-COMMS] Message buffer too small.\n");
+		return -1;
+	}
+	message_len += len;
+
+	*payload_len = message_len;
+	return 0;
+}
+
+static void unpack_params(const uint8_t *buf,
+			  psa_outvec *outvecs,
+			  size_t out_len)
+{
+	size_t i;
+
+	for (i = 0U; i < out_len; ++i) {
+		memcpy(outvecs[i].base, buf, outvecs[i].len);
+		buf += outvecs[i].len;
+	}
+}
+
+static void deserialise_reply(struct packed_psa_reply_t *reply,
+			      psa_outvec *outvecs,
+			      size_t outlen,
+			      const uint8_t *message,
+			      size_t message_len)
+{
+	uint32_t i;
+
+	memcpy(reply, message, sizeof(*reply));
+
+	/* Outvecs */
+	for (i = 0U; i < outlen; ++i) {
+		outvecs[i].len = reply->out_size[i];
+	}
+
+	unpack_params(message + sizeof(*reply), outvecs, outlen);
+}
+
+psa_status_t psa_call(psa_handle_t handle, int32_t type,
+		      const psa_invec *in_vec, size_t in_len,
+		      psa_outvec *out_vec, size_t out_len)
+{
+	enum mhu_error_t err;
+	static uint32_t seq_num = 1U;
+	struct packed_psa_call_t msg = {
+		.protocol_ver = 0U,
+		.seq_num = seq_num,
+		/* No need to distinguish callers (currently concurrent calls are not supported). */
+		.client_id = 1U,
+		.handle = handle,
+		.ctrl_param = PARAM_PACK(type, in_len, out_len),
+	};
+
+	struct packed_psa_reply_t reply = {0};
+	size_t message_size;
+	uint32_t i;
+
+	/* Fill msg iovec lengths */
+	for (i = 0U; i < in_len; ++i) {
+		msg.io_size[i] = in_vec[i].len;
+	}
+	for (i = 0U; i < out_len; ++i) {
+		msg.io_size[in_len + i] = out_vec[i].len;
+	}
+
+	message_size = sizeof(message_buf);
+	if (serialise_message(&msg, in_vec, message_buf, &message_size)) {
+		/* Local buffer is probably too small. */
+		return PSA_ERROR_INSUFFICIENT_MEMORY;
+	}
+
+	err = mhu_send_data(message_buf, message_size);
+	if (err != MHU_ERR_NONE) {
+		return PSA_ERROR_COMMUNICATION_FAILURE;
+	}
+
+	message_size = sizeof(message_buf);
+#if DEBUG
+	/*
+	 * Poisoning the message buffer (with a known pattern).
+	 * Helps in detecting hypothetical RSS communication bugs.
+	 */
+	memset(message_buf, 0xA5, message_size);
+#endif
+	err = mhu_receive_data(message_buf, &message_size);
+	if (err != MHU_ERR_NONE) {
+		return PSA_ERROR_COMMUNICATION_FAILURE;
+	}
+
+	deserialise_reply(&reply, out_vec, out_len, message_buf, message_size);
+
+	seq_num++;
+
+	VERBOSE("[RSS-COMMS] Received reply\n");
+	VERBOSE("protocol_ver=%d\n", reply.protocol_ver);
+	VERBOSE("seq_num=%d\n", reply.seq_num);
+	VERBOSE("client_id=%d\n", reply.client_id);
+	VERBOSE("return_val=%d\n", reply.return_val);
+	VERBOSE("out_size[0]=%d\n", reply.out_size[0]);
+
+	return reply.return_val;
+}
+
+int rss_comms_init(uintptr_t mhu_sender_base, uintptr_t mhu_receiver_base)
+{
+	enum mhu_error_t err;
+
+	err = mhu_init_sender(mhu_sender_base);
+	if (err != MHU_ERR_NONE) {
+		ERROR("[RSS-COMMS] Host to RSS MHU driver initialization failed: %d\n", err);
+		return -1;
+	}
+
+	err = mhu_init_receiver(mhu_receiver_base);
+	if (err != MHU_ERR_NONE) {
+		ERROR("[RSS-COMMS] RSS to Host MHU driver initialization failed: %d\n", err);
+		return -1;
+	}
+
+	return 0;
+}