diff --git a/drivers/st/scmi-msg/smt.c b/drivers/st/scmi-msg/smt.c
new file mode 100644
index 0000000..2d5cd73
--- /dev/null
+++ b/drivers/st/scmi-msg/smt.c
@@ -0,0 +1,206 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Copyright (c) 2015-2019, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2019-2020, Linaro Limited
+ */
+#include <assert.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <drivers/st/scmi-msg.h>
+#include <drivers/st/scmi.h>
+#include <lib/cassert.h>
+#include <lib/mmio.h>
+#include <lib/spinlock.h>
+#include <lib/utils.h>
+#include <plat/common/platform.h>
+
+#include "common.h"
+
+/* Legacy SMT/SCMI messages are 128 bytes at most including SMT header */
+#define SCMI_PLAYLOAD_MAX		92U
+#define SCMI_PLAYLOAD_U32_MAX		(SCMI_PLAYLOAD_MAX / sizeof(uint32_t))
+
+/**
+ * struct smt_header - SMT formatted header for SMT base shared memory transfer
+ *
+ * @status: Bit flags, see SMT_STATUS_*
+ * @flags: Bit flags, see SMT_FLAG_*
+ * @length: Byte size of message payload (variable) + ::message_header (32bit)
+ * payload: SCMI message payload data
+ */
+struct smt_header {
+	uint32_t reserved0;
+	uint32_t status;
+	uint64_t reserved1;
+	uint32_t flags;
+	uint32_t length; /* message_header + payload */
+	uint32_t message_header;
+	uint32_t payload[];
+};
+
+CASSERT(SCMI_PLAYLOAD_MAX + sizeof(struct smt_header) <= SMT_BUF_SLOT_SIZE,
+	assert_scmi_message_max_length_fits_in_smt_buffer_slot);
+
+/* Flag set in smt_header::status when SMT does not contain pending message */
+#define SMT_STATUS_FREE			BIT(0)
+/* Flag set in smt_header::status when SMT reports an error */
+#define SMT_STATUS_ERROR		BIT(1)
+
+/* Flag set in smt_header::flags when SMT uses interrupts */
+#define SMT_FLAG_INTR_ENABLED		BIT(1)
+
+/* Bit fields packed in smt_header::message_header */
+#define SMT_MSG_ID_MASK			GENMASK_32(7, 0)
+#define SMT_HDR_MSG_ID(_hdr)		((_hdr) & SMT_MSG_ID_MASK)
+
+#define SMT_MSG_TYPE_MASK		GENMASK_32(9, 8)
+#define SMT_HDR_TYPE_ID(_hdr)		(((_hdr) & SMT_MSG_TYPE_MASK) >> 8)
+
+#define SMT_MSG_PROT_ID_MASK		GENMASK_32(17, 10)
+#define SMT_HDR_PROT_ID(_hdr)		(((_hdr) & SMT_MSG_PROT_ID_MASK) >> 10)
+
+/*
+ * Provision input message payload buffers for fastcall SMC context entries
+ * and for interrupt context execution entries.
+ */
+static uint32_t fast_smc_payload[PLATFORM_CORE_COUNT][SCMI_PLAYLOAD_U32_MAX];
+static uint32_t interrupt_payload[PLATFORM_CORE_COUNT][SCMI_PLAYLOAD_U32_MAX];
+
+/* SMP protection on channel access */
+static struct spinlock smt_channels_lock;
+
+/* If channel is not busy, set busy and return true, otherwise return false */
+static bool channel_set_busy(struct scmi_msg_channel *chan)
+{
+	bool channel_is_busy;
+
+	spin_lock(&smt_channels_lock);
+
+	channel_is_busy = chan->busy;
+
+	if (!channel_is_busy) {
+		chan->busy = true;
+	}
+
+	spin_unlock(&smt_channels_lock);
+
+	return !channel_is_busy;
+}
+
+static void channel_release_busy(struct scmi_msg_channel *chan)
+{
+	chan->busy = false;
+}
+
+static struct smt_header *channel_to_smt_hdr(struct scmi_msg_channel *chan)
+{
+	return (struct smt_header *)chan->shm_addr;
+}
+
+/*
+ * Creates a SCMI message instance in secure memory and pushes it in the SCMI
+ * message drivers. Message structure contains SCMI protocol meta-data and
+ * references to input payload in secure memory and output message buffer
+ * in shared memory.
+ */
+static void scmi_proccess_smt(unsigned int agent_id, uint32_t *payload_buf)
+{
+	struct scmi_msg_channel *chan;
+	struct smt_header *smt_hdr;
+	size_t in_payload_size;
+	uint32_t smt_status;
+	struct scmi_msg msg;
+	bool error = true;
+
+	chan = plat_scmi_get_channel(agent_id);
+	if (chan == NULL) {
+		return;
+	}
+
+	smt_hdr = channel_to_smt_hdr(chan);
+	assert(smt_hdr);
+
+	smt_status = __atomic_load_n(&smt_hdr->status, __ATOMIC_RELAXED);
+
+	if (!channel_set_busy(chan)) {
+		VERBOSE("SCMI channel %u busy", agent_id);
+		goto out;
+	}
+
+	in_payload_size = __atomic_load_n(&smt_hdr->length, __ATOMIC_RELAXED) -
+			  sizeof(smt_hdr->message_header);
+
+	if (in_payload_size > SCMI_PLAYLOAD_MAX) {
+		VERBOSE("SCMI payload too big %u", in_payload_size);
+		goto out;
+	}
+
+	if ((smt_status & (SMT_STATUS_ERROR | SMT_STATUS_FREE)) != 0U) {
+		VERBOSE("SCMI channel bad status 0x%x",
+			smt_hdr->status & (SMT_STATUS_ERROR | SMT_STATUS_FREE));
+		goto out;
+	}
+
+	/* Fill message */
+	zeromem(&msg, sizeof(msg));
+	msg.in = (char *)payload_buf;
+	msg.in_size = in_payload_size;
+	msg.out = (char *)smt_hdr->payload;
+	msg.out_size = chan->shm_size - sizeof(*smt_hdr);
+
+	assert((msg.out != NULL) && (msg.out_size >= sizeof(int32_t)));
+
+	/* Here the payload is copied in secure memory */
+	memcpy(msg.in, smt_hdr->payload, in_payload_size);
+
+	msg.protocol_id = SMT_HDR_PROT_ID(smt_hdr->message_header);
+	msg.message_id = SMT_HDR_MSG_ID(smt_hdr->message_header);
+	msg.agent_id = agent_id;
+
+	scmi_process_message(&msg);
+
+	/* Update message length with the length of the response message */
+	smt_hdr->length = msg.out_size_out + sizeof(smt_hdr->message_header);
+
+	channel_release_busy(chan);
+	error = false;
+
+out:
+	if (error) {
+		VERBOSE("SCMI error");
+		smt_hdr->status |= SMT_STATUS_ERROR | SMT_STATUS_FREE;
+	} else {
+		smt_hdr->status |= SMT_STATUS_FREE;
+	}
+}
+
+void scmi_smt_fastcall_smc_entry(unsigned int agent_id)
+{
+	scmi_proccess_smt(agent_id,
+			  fast_smc_payload[plat_my_core_pos()]);
+}
+
+void scmi_smt_interrupt_entry(unsigned int agent_id)
+{
+	scmi_proccess_smt(agent_id,
+			  interrupt_payload[plat_my_core_pos()]);
+}
+
+/* Init a SMT header for a shared memory buffer: state it a free/no-error */
+void scmi_smt_init_agent_channel(struct scmi_msg_channel *chan)
+{
+	if (chan != NULL) {
+		struct smt_header *smt_header = channel_to_smt_hdr(chan);
+
+		if (smt_header != NULL) {
+			memset(smt_header, 0, sizeof(*smt_header));
+			smt_header->status = SMT_STATUS_FREE;
+
+			return;
+		}
+	}
+
+	panic();
+}
diff --git a/include/drivers/st/scmi-msg.h b/include/drivers/st/scmi-msg.h
index 8f7a788..a9a99cf 100644
--- a/include/drivers/st/scmi-msg.h
+++ b/include/drivers/st/scmi-msg.h
@@ -32,6 +32,32 @@
 	const char *agent_name;
 };
 
+/*
+ * Initialize SMT memory buffer, called by platform at init for each
+ * agent channel using the SMT header format.
+ *
+ * @chan: Pointer to the channel shared memory to be initialized
+ */
+void scmi_smt_init_agent_channel(struct scmi_msg_channel *chan);
+
+/*
+ * Process SMT formatted message in a fastcall SMC execution context.
+ * Called by platform on SMC entry. When returning, output message is
+ * available in shared memory for agent to read the response.
+ *
+ * @agent_id: SCMI agent ID the SMT belongs to
+ */
+void scmi_smt_fastcall_smc_entry(unsigned int agent_id);
+
+/*
+ * Process SMT formatted message in a secure interrupt execution context.
+ * Called by platform interrupt handler. When returning, output message is
+ * available in shared memory for agent to read the response.
+ *
+ * @agent_id: SCMI agent ID the SMT belongs to
+ */
+void scmi_smt_interrupt_entry(unsigned int agent_id);
+
 /* Platform callback functions */
 
 /*