diff mbox series

[5/5] firmware: scmi: Add OP-TEE transport

Message ID 20211104141451.29967-5-etienne.carriere@linaro.org
State Superseded
Headers show
Series [1/5] tee: define session login identifiers | expand

Commit Message

Etienne Carriere Nov. 4, 2021, 2:14 p.m. UTC 
This change implements an SCMI transport for agent interfacing the
OP-TEE SCMI service. OP-TEE provides an SCMI PTA (Pseudo-TA) for
non-secure world to send SCMI messages over an identified channel.
The driver implemented here uses a SMT shared memory for passing
messages between client and server.

The implementation opens and releases channel resources for each
passed SCMI message so that resources allocated (sessions) or
registered (shared memory areas) in OP-TEE firmware are released for
example before relocation as the driver will likely allocate/register
them back when probed after relocation.

The integration of the driver using dedicated config switch
CONFIG_SCMI_AGENT_OPTEE is designed on the model posted to the
U-Boot ML by Patrick Delaunay [1].

Link: [1] https://lore.kernel.org/all/20211028191222.v3.4.Ib2e58ee67f4d023823d8b5404332dc4d7e847277@changeid/
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Cc: Wolfgang Denk <wd@denx.de>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
---
 drivers/firmware/scmi/Kconfig       |  14 +-
 drivers/firmware/scmi/Makefile      |   1 +
 drivers/firmware/scmi/optee_agent.c | 312 ++++++++++++++++++++++++++++
 3 files changed, 324 insertions(+), 3 deletions(-)
 create mode 100644 drivers/firmware/scmi/optee_agent.c

-- 
2.17.1

Comments

Patrick DELAUNAY Nov. 8, 2021, 9:37 a.m. UTC | #1 
Hi,

On 11/4/21 3:14 PM, Etienne Carriere wrote:
> This change implements an SCMI transport for agent interfacing the
> OP-TEE SCMI service. OP-TEE provides an SCMI PTA (Pseudo-TA) for
> non-secure world to send SCMI messages over an identified channel.
> The driver implemented here uses a SMT shared memory for passing
> messages between client and server.
>
> The implementation opens and releases channel resources for each
> passed SCMI message so that resources allocated (sessions) or
> registered (shared memory areas) in OP-TEE firmware are released for
> example before relocation as the driver will likely allocate/register
> them back when probed after relocation.
>
> The integration of the driver using dedicated config switch
> CONFIG_SCMI_AGENT_OPTEE is designed on the model posted to the
> U-Boot ML by Patrick Delaunay [1].
>
> Link: [1] https://lore.kernel.org/all/20211028191222.v3.4.Ib2e58ee67f4d023823d8b5404332dc4d7e847277@changeid/
> Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
> Cc: Wolfgang Denk <wd@denx.de>
> Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
> ---
>   drivers/firmware/scmi/Kconfig       |  14 +-
>   drivers/firmware/scmi/Makefile      |   1 +
>   drivers/firmware/scmi/optee_agent.c | 312 ++++++++++++++++++++++++++++
>   3 files changed, 324 insertions(+), 3 deletions(-)
>   create mode 100644 drivers/firmware/scmi/optee_agent.c
>

Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>

Thanks
Patrick
Patrick DELAUNAY Nov. 9, 2021, 2:39 p.m. UTC | #2 
Hi Etienne,

one missing remark, don't see in my first review.

On 11/4/21 3:14 PM, Etienne Carriere wrote:
> This change implements an SCMI transport for agent interfacing the
> OP-TEE SCMI service. OP-TEE provides an SCMI PTA (Pseudo-TA) for
> non-secure world to send SCMI messages over an identified channel.
> The driver implemented here uses a SMT shared memory for passing
> messages between client and server.
>
> The implementation opens and releases channel resources for each
> passed SCMI message so that resources allocated (sessions) or
> registered (shared memory areas) in OP-TEE firmware are released for
> example before relocation as the driver will likely allocate/register
> them back when probed after relocation.
>
> The integration of the driver using dedicated config switch
> CONFIG_SCMI_AGENT_OPTEE is designed on the model posted to the
> U-Boot ML by Patrick Delaunay [1].
>
> Link: [1] https://lore.kernel.org/all/20211028191222.v3.4.Ib2e58ee67f4d023823d8b5404332dc4d7e847277@changeid/
> Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
> Cc: Wolfgang Denk <wd@denx.de>
> Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
> ---
>   drivers/firmware/scmi/Kconfig       |  14 +-
>   drivers/firmware/scmi/Makefile      |   1 +
>   drivers/firmware/scmi/optee_agent.c | 312 ++++++++++++++++++++++++++++
>   3 files changed, 324 insertions(+), 3 deletions(-)
>   create mode 100644 drivers/firmware/scmi/optee_agent.c
>
> diff --git a/drivers/firmware/scmi/Kconfig b/drivers/firmware/scmi/Kconfig
> index c3a109beac..f9c69e5352 100644
> --- a/drivers/firmware/scmi/Kconfig
> +++ b/drivers/firmware/scmi/Kconfig
> @@ -2,7 +2,7 @@ config SCMI_FIRMWARE
>   	bool "Enable SCMI support"
>   	select FIRMWARE
>   	select OF_TRANSLATE
> -	depends on SANDBOX || DM_MAILBOX || ARM_SMCCC
> +	depends on SANDBOX || DM_MAILBOX || ARM_SMCCC || OPTEE
>   	help
>   	  System Control and Management Interface (SCMI) is a communication
>   	  protocol that defines standard interfaces for power, performance
> @@ -14,6 +14,14 @@ config SCMI_FIRMWARE
>   	  or a companion host in the CPU system.
>   
>   	  Communications between agent (client) and the SCMI server are
> -	  based on message exchange. Messages can be exchange over tranport
> +	  based on message exchange. Messages can be exchanged over transport
>   	  channels as a mailbox device or an Arm SMCCC service with some
> -	  piece of identified shared memory.
> +	  piece of identified shared memory, or an OP-TEE SCMI service.
> +
> +config SCMI_AGENT_OPTEE
> +	bool "Enable SCMI agent OP-TEE"
> +	depends on SCMI_FIRMWARE && OPTEE
> +	default y
> +	help
> +	  Enable the SCMI communication channel based on OP-TEE transport
> +	  for compatible "linaro,scmi-optee".
> diff --git a/drivers/firmware/scmi/Makefile b/drivers/firmware/scmi/Makefile
> index 966475ec10..f72d06a400 100644
> --- a/drivers/firmware/scmi/Makefile
> +++ b/drivers/firmware/scmi/Makefile
> @@ -2,4 +2,5 @@ obj-y	+= scmi_agent-uclass.o
>   obj-y	+= smt.o
>   obj-$(CONFIG_ARM_SMCCC)		+= smccc_agent.o
>   obj-$(CONFIG_DM_MAILBOX)	+= mailbox_agent.o
> +obj-$(CONFIG_SCMI_AGENT_OPTEE)	+= optee_agent.o
>   obj-$(CONFIG_SANDBOX)		+= sandbox-scmi_agent.o sandbox-scmi_devices.o
> diff --git a/drivers/firmware/scmi/optee_agent.c b/drivers/firmware/scmi/optee_agent.c
> new file mode 100644
> index 0000000000..8232af2f41
> --- /dev/null
> +++ b/drivers/firmware/scmi/optee_agent.c
> @@ -0,0 +1,312 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (C) 2020-2021 Linaro Limited.
> + */
> +

(...)

> +
> +static int scmi_optee_of_to_plat(struct udevice *dev)
> +{
> +	struct scmi_optee_channel *chan = dev_get_plat(dev);
> +	int ret;
> +
> +	if (dev_read_u32(dev, "linaro,optee-channel-id", &chan->channel_id)) {
> +		dev_err(dev, "Missing property linaro,channel-id\n");

Can you use the correct property name in the error message = "linaro,optee-channel-id"

+		dev_err(dev, "Missing property linaro,optee-channel-id\n");


Patrick
Etienne Carriere Nov. 9, 2021, 3:44 p.m. UTC | #3 
On Tue, 9 Nov 2021 at 15:39, Patrick DELAUNAY
<patrick.delaunay@foss.st.com> wrote:
>
> Hi Etienne,
>
> one missing remark, don't see in my first review.
>
> On 11/4/21 3:14 PM, Etienne Carriere wrote:
> > This change implements an SCMI transport for agent interfacing the
> > OP-TEE SCMI service. OP-TEE provides an SCMI PTA (Pseudo-TA) for
> > non-secure world to send SCMI messages over an identified channel.
> > The driver implemented here uses a SMT shared memory for passing
> > messages between client and server.
> >
> > The implementation opens and releases channel resources for each
> > passed SCMI message so that resources allocated (sessions) or
> > registered (shared memory areas) in OP-TEE firmware are released for
> > example before relocation as the driver will likely allocate/register
> > them back when probed after relocation.
> >
> > The integration of the driver using dedicated config switch
> > CONFIG_SCMI_AGENT_OPTEE is designed on the model posted to the
> > U-Boot ML by Patrick Delaunay [1].
> >
> > Link: [1] https://lore.kernel.org/all/20211028191222.v3.4.Ib2e58ee67f4d023823d8b5404332dc4d7e847277@changeid/
> > Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
> > Cc: Wolfgang Denk <wd@denx.de>
> > Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
> > ---
> >   drivers/firmware/scmi/Kconfig       |  14 +-
> >   drivers/firmware/scmi/Makefile      |   1 +
> >   drivers/firmware/scmi/optee_agent.c | 312 ++++++++++++++++++++++++++++
> >   3 files changed, 324 insertions(+), 3 deletions(-)
> >   create mode 100644 drivers/firmware/scmi/optee_agent.c
> >
> > diff --git a/drivers/firmware/scmi/Kconfig b/drivers/firmware/scmi/Kconfig
> > index c3a109beac..f9c69e5352 100644
> > --- a/drivers/firmware/scmi/Kconfig
> > +++ b/drivers/firmware/scmi/Kconfig
> > @@ -2,7 +2,7 @@ config SCMI_FIRMWARE
> >       bool "Enable SCMI support"
> >       select FIRMWARE
> >       select OF_TRANSLATE
> > -     depends on SANDBOX || DM_MAILBOX || ARM_SMCCC
> > +     depends on SANDBOX || DM_MAILBOX || ARM_SMCCC || OPTEE
> >       help
> >         System Control and Management Interface (SCMI) is a communication
> >         protocol that defines standard interfaces for power, performance
> > @@ -14,6 +14,14 @@ config SCMI_FIRMWARE
> >         or a companion host in the CPU system.
> >
> >         Communications between agent (client) and the SCMI server are
> > -       based on message exchange. Messages can be exchange over tranport
> > +       based on message exchange. Messages can be exchanged over transport
> >         channels as a mailbox device or an Arm SMCCC service with some
> > -       piece of identified shared memory.
> > +       piece of identified shared memory, or an OP-TEE SCMI service.
> > +
> > +config SCMI_AGENT_OPTEE
> > +     bool "Enable SCMI agent OP-TEE"
> > +     depends on SCMI_FIRMWARE && OPTEE
> > +     default y
> > +     help
> > +       Enable the SCMI communication channel based on OP-TEE transport
> > +       for compatible "linaro,scmi-optee".
> > diff --git a/drivers/firmware/scmi/Makefile b/drivers/firmware/scmi/Makefile
> > index 966475ec10..f72d06a400 100644
> > --- a/drivers/firmware/scmi/Makefile
> > +++ b/drivers/firmware/scmi/Makefile
> > @@ -2,4 +2,5 @@ obj-y += scmi_agent-uclass.o
> >   obj-y       += smt.o
> >   obj-$(CONFIG_ARM_SMCCC)             += smccc_agent.o
> >   obj-$(CONFIG_DM_MAILBOX)    += mailbox_agent.o
> > +obj-$(CONFIG_SCMI_AGENT_OPTEE)       += optee_agent.o
> >   obj-$(CONFIG_SANDBOX)               += sandbox-scmi_agent.o sandbox-scmi_devices.o
> > diff --git a/drivers/firmware/scmi/optee_agent.c b/drivers/firmware/scmi/optee_agent.c
> > new file mode 100644
> > index 0000000000..8232af2f41
> > --- /dev/null
> > +++ b/drivers/firmware/scmi/optee_agent.c
> > @@ -0,0 +1,312 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +/*
> > + * Copyright (C) 2020-2021 Linaro Limited.
> > + */
> > +
>
> (...)
>
> > +
> > +static int scmi_optee_of_to_plat(struct udevice *dev)
> > +{
> > +     struct scmi_optee_channel *chan = dev_get_plat(dev);
> > +     int ret;
> > +
> > +     if (dev_read_u32(dev, "linaro,optee-channel-id", &chan->channel_id)) {
> > +             dev_err(dev, "Missing property linaro,channel-id\n");
>
> Can you use the correct property name in the error message = "linaro,optee-channel-id"
>
> +               dev_err(dev, "Missing property linaro,optee-channel-id\n");
>

nice catch.
Thanks, I'll post a v2.

Etienne

>
> Patrick
>
diff mbox series

Patch

diff --git a/drivers/firmware/scmi/Kconfig b/drivers/firmware/scmi/Kconfig
index c3a109beac..f9c69e5352 100644
--- a/drivers/firmware/scmi/Kconfig
+++ b/drivers/firmware/scmi/Kconfig
@@ -2,7 +2,7 @@  config SCMI_FIRMWARE
 	bool "Enable SCMI support"
 	select FIRMWARE
 	select OF_TRANSLATE
-	depends on SANDBOX || DM_MAILBOX || ARM_SMCCC
+	depends on SANDBOX || DM_MAILBOX || ARM_SMCCC || OPTEE
 	help
 	  System Control and Management Interface (SCMI) is a communication
 	  protocol that defines standard interfaces for power, performance
@@ -14,6 +14,14 @@  config SCMI_FIRMWARE
 	  or a companion host in the CPU system.
 
 	  Communications between agent (client) and the SCMI server are
-	  based on message exchange. Messages can be exchange over tranport
+	  based on message exchange. Messages can be exchanged over transport
 	  channels as a mailbox device or an Arm SMCCC service with some
-	  piece of identified shared memory.
+	  piece of identified shared memory, or an OP-TEE SCMI service.
+
+config SCMI_AGENT_OPTEE
+	bool "Enable SCMI agent OP-TEE"
+	depends on SCMI_FIRMWARE && OPTEE
+	default y
+	help
+	  Enable the SCMI communication channel based on OP-TEE transport
+	  for compatible "linaro,scmi-optee".
diff --git a/drivers/firmware/scmi/Makefile b/drivers/firmware/scmi/Makefile
index 966475ec10..f72d06a400 100644
--- a/drivers/firmware/scmi/Makefile
+++ b/drivers/firmware/scmi/Makefile
@@ -2,4 +2,5 @@  obj-y	+= scmi_agent-uclass.o
 obj-y	+= smt.o
 obj-$(CONFIG_ARM_SMCCC)		+= smccc_agent.o
 obj-$(CONFIG_DM_MAILBOX)	+= mailbox_agent.o
+obj-$(CONFIG_SCMI_AGENT_OPTEE)	+= optee_agent.o
 obj-$(CONFIG_SANDBOX)		+= sandbox-scmi_agent.o sandbox-scmi_devices.o
diff --git a/drivers/firmware/scmi/optee_agent.c b/drivers/firmware/scmi/optee_agent.c
new file mode 100644
index 0000000000..8232af2f41
--- /dev/null
+++ b/drivers/firmware/scmi/optee_agent.c
@@ -0,0 +1,312 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2020-2021 Linaro Limited.
+ */
+
+#define LOG_CATEGORY UCLASS_SCMI_AGENT
+
+#include <common.h>
+#include <dm.h>
+#include <errno.h>
+#include <scmi_agent.h>
+#include <scmi_agent-uclass.h>
+#include <string.h>
+#include <tee.h>
+#include <asm/types.h>
+#include <dm/device_compat.h>
+#include <dm/devres.h>
+#include <linux/arm-smccc.h>
+#include <linux/bug.h>
+#include <linux/compat.h>
+
+#include "smt.h"
+
+#define SCMI_SHM_SIZE		128
+
+/**
+ * struct scmi_optee_channel - Description of an SCMI OP-TEE transport
+ * @channel_id:		Channel identifier
+ * @smt:		Shared memory buffer with synchronisation protocol
+ * @dyn_shm:		True if using dynamically allocated shared memory
+ */
+struct scmi_optee_channel {
+	unsigned int channel_id;
+	struct scmi_smt smt;
+	bool dyn_shm;
+};
+
+/**
+ * struct channel_session - Aggreates SCMI service session context references
+ * @tee:		OP-TEE device to invoke
+ * @tee_session:	OP-TEE session identifier
+ * @tee_shm:		Dynamically allocated OP-TEE shared memory, or NULL
+ * @channel_hdl:	Channel handle provided by OP-TEE SCMI service
+ */
+struct channel_session {
+	struct udevice *tee;
+	u32 tee_session;
+	struct tee_shm *tee_shm;
+	u32 channel_hdl;
+};
+
+#define TA_SCMI_UUID { 0xa8cfe406, 0xd4f5, 0x4a2e, \
+		      { 0x9f, 0x8d, 0xa2, 0x5d, 0xc7, 0x54, 0xc0, 0x99 } }
+
+enum optee_smci_pta_cmd {
+	/*
+	 * PTA_SCMI_CMD_CAPABILITIES - Get channel capabilities
+	 *
+	 * [out]    value[0].a: Capability bit mask (enum pta_scmi_caps)
+	 * [out]    value[0].b: Extended capabilities or 0
+	 */
+	PTA_SCMI_CMD_CAPABILITIES = 0,
+
+	/*
+	 * PTA_SCMI_CMD_PROCESS_SMT_CHANNEL - Process SCMI message in SMT buffer
+	 *
+	 * [in]     value[0].a: Channel handle
+	 *
+	 * Shared memory used for SCMI message/response exhange is expected
+	 * already identified and bound to channel handle in both SCMI agent
+	 * and SCMI server (OP-TEE) parts.
+	 * The memory uses SMT header to carry SCMI meta-data (protocol ID and
+	 * protocol message ID).
+	 */
+	PTA_SCMI_CMD_PROCESS_SMT_CHANNEL = 1,
+
+	/*
+	 * PTA_SCMI_CMD_PROCESS_SMT_CHANNEL_MESSAGE - Process SMT/SCMI message
+	 *
+	 * [in]     value[0].a: Channel handle
+	 * [in/out] memref[1]: Message/response buffer (SMT and SCMI payload)
+	 *
+	 * Shared memory used for SCMI message/response is a SMT buffer
+	 * referenced by param[1]. It shall be 128 bytes large to fit response
+	 * payload whatever message playload size.
+	 * The memory uses SMT header to carry SCMI meta-data (protocol ID and
+	 * protocol message ID).
+	 */
+	PTA_SCMI_CMD_PROCESS_SMT_CHANNEL_MESSAGE = 2,
+
+	/*
+	 * PTA_SCMI_CMD_GET_CHANNEL - Get channel handle
+	 *
+	 * SCMI shm information are 0 if agent expects to use OP-TEE regular SHM
+	 *
+	 * [in]     value[0].a: Channel identifier
+	 * [out]    value[0].a: Returned channel handle
+	 * [in]     value[0].b: Requested capabilities mask (enum pta_scmi_caps)
+	 */
+	PTA_SCMI_CMD_GET_CHANNEL = 3,
+};
+
+/*
+ * OP-TEE SCMI service capabilities bit flags (32bit)
+ *
+ * PTA_SCMI_CAPS_SMT_HEADER
+ * When set, OP-TEE supports command using SMT header protocol (SCMI shmem) in
+ * shared memory buffers to carry SCMI protocol synchronisation information.
+ */
+#define PTA_SCMI_CAPS_NONE		0
+#define PTA_SCMI_CAPS_SMT_HEADER	BIT(0)
+
+static int open_channel(struct udevice *dev, struct channel_session *sess)
+{
+	const struct tee_optee_ta_uuid uuid = TA_SCMI_UUID;
+	struct scmi_optee_channel *chan = dev_get_plat(dev);
+	struct tee_open_session_arg sess_arg = { };
+	struct tee_invoke_arg cmd_arg = { };
+	struct tee_param param[1] = { };
+	int ret;
+
+	memset(sess, 0, sizeof(sess));
+
+	sess->tee = tee_find_device(NULL, NULL, NULL, NULL);
+	if (!sess->tee)
+		return -ENODEV;
+
+	sess_arg.clnt_login = TEE_LOGIN_REE_KERNEL;
+	tee_optee_ta_uuid_to_octets(sess_arg.uuid, &uuid);
+
+	ret = tee_open_session(sess->tee, &sess_arg, 0, NULL);
+	if (ret) {
+		dev_err(dev, "can't open session: %d\n", ret);
+		return ret;
+	}
+
+	cmd_arg.func = PTA_SCMI_CMD_GET_CHANNEL;
+	cmd_arg.session = sess_arg.session;
+
+	param[0].attr = TEE_PARAM_ATTR_TYPE_VALUE_INOUT;
+	param[0].u.value.a = chan->channel_id;
+	param[0].u.value.b = PTA_SCMI_CAPS_SMT_HEADER;
+
+	ret = tee_invoke_func(sess->tee, &cmd_arg, ARRAY_SIZE(param), param);
+	if (ret || cmd_arg.ret) {
+		dev_err(dev, "Invoke failed: %d, 0x%x\n", ret, cmd_arg.ret);
+		if (!ret)
+			ret = -EPROTO;
+
+		tee_close_session(sess->tee, sess_arg.session);
+		return ret;
+	}
+
+	sess->tee_session = sess_arg.session;
+	sess->channel_hdl = param[0].u.value.a;
+
+	return 0;
+}
+
+static void close_channel(struct channel_session *sess)
+{
+	tee_close_session(sess->tee, sess->tee_session);
+}
+
+static int invoke_cmd(struct udevice *dev, struct channel_session *sess,
+		      struct scmi_msg *msg)
+{
+	struct scmi_optee_channel *chan = dev_get_plat(dev);
+	struct tee_invoke_arg arg = { };
+	struct tee_param param[2] = { };
+	int ret;
+
+	scmi_write_msg_to_smt(dev, &chan->smt, msg);
+
+	arg.session = sess->tee_session;
+	param[0].attr = TEE_PARAM_ATTR_TYPE_VALUE_INPUT;
+	param[0].u.value.a = sess->channel_hdl;
+
+	if (chan->dyn_shm) {
+		arg.func = PTA_SCMI_CMD_PROCESS_SMT_CHANNEL_MESSAGE;
+		param[1].attr = TEE_PARAM_ATTR_TYPE_MEMREF_INOUT;
+		param[1].u.memref.shm = sess->tee_shm;
+		param[1].u.memref.size = SCMI_SHM_SIZE;
+	} else {
+		arg.func = PTA_SCMI_CMD_PROCESS_SMT_CHANNEL;
+	}
+
+	ret = tee_invoke_func(sess->tee, &arg, ARRAY_SIZE(param), param);
+	if (ret || arg.ret) {
+		if (!ret)
+			ret = -EPROTO;
+	} else {
+		ret = scmi_read_resp_from_smt(dev, &chan->smt, msg);
+	}
+
+	scmi_clear_smt_channel(&chan->smt);
+
+	return ret;
+}
+
+static int prepare_shm(struct udevice *dev, struct channel_session *sess)
+{
+	struct scmi_optee_channel *chan = dev_get_plat(dev);
+	int ret;
+
+	/* Static shm is already prepared by the firmware: nothing to do */
+	if (!chan->dyn_shm)
+		return 0;
+
+	chan->smt.size = SCMI_SHM_SIZE;
+
+	ret = tee_shm_alloc(sess->tee, chan->smt.size, 0, &sess->tee_shm);
+	if (ret) {
+		dev_err(dev, "Failed to allocated shmem: %d\n", ret);
+		return ret;
+	}
+
+	chan->smt.buf = sess->tee_shm->addr;
+
+	/* Initialize shm buffer for message exchanges */
+	scmi_clear_smt_channel(&chan->smt);
+
+	return 0;
+}
+
+static void release_shm(struct udevice *dev, struct channel_session *sess)
+{
+	struct scmi_optee_channel *chan = dev_get_plat(dev);
+
+	if (chan->dyn_shm)
+		tee_shm_free(sess->tee_shm);
+}
+
+static int scmi_optee_process_msg(struct udevice *dev, struct scmi_msg *msg)
+{
+	struct channel_session sess;
+	int ret;
+
+	ret = open_channel(dev, &sess);
+	if (ret)
+		return ret;
+
+	ret = prepare_shm(dev, &sess);
+	if (ret)
+		goto out;
+
+	ret = invoke_cmd(dev, &sess, msg);
+
+	release_shm(dev, &sess);
+
+out:
+	close_channel(&sess);
+
+	return ret;
+}
+
+static int scmi_optee_of_to_plat(struct udevice *dev)
+{
+	struct scmi_optee_channel *chan = dev_get_plat(dev);
+	int ret;
+
+	if (dev_read_u32(dev, "linaro,optee-channel-id", &chan->channel_id)) {
+		dev_err(dev, "Missing property linaro,channel-id\n");
+		return -EINVAL;
+	}
+
+	if (dev_read_prop(dev, "shmem", NULL)) {
+		ret = scmi_dt_get_smt_buffer(dev, &chan->smt);
+		if (ret) {
+			dev_err(dev, "Failed to get smt resources: %d\n", ret);
+			return ret;
+		}
+		chan->dyn_shm = false;
+	} else {
+		chan->dyn_shm = true;
+	}
+
+	return 0;
+}
+
+static int scmi_optee_probe(struct udevice *dev)
+{
+	struct channel_session sess;
+	int ret;
+
+	/* Check OP-TEE service acknowledges the SCMI channel */
+	ret = open_channel(dev, &sess);
+	if (!ret)
+		close_channel(&sess);
+
+	return ret;
+}
+
+static const struct udevice_id scmi_optee_ids[] = {
+	{ .compatible = "linaro,scmi-optee" },
+	{ }
+};
+
+static const struct scmi_agent_ops scmi_optee_ops = {
+	.process_msg = scmi_optee_process_msg,
+};
+
+U_BOOT_DRIVER(scmi_optee) = {
+	.name		= "scmi-over-optee",
+	.id		= UCLASS_SCMI_AGENT,
+	.of_match	= scmi_optee_ids,
+	.plat_auto	= sizeof(struct scmi_optee_channel),
+	.of_to_plat	= scmi_optee_of_to_plat,
+	.probe		= scmi_optee_probe,
+	.flags		= DM_FLAG_OS_PREPARE,
+	.ops		= &scmi_optee_ops,
+};