Add MCTP over USB Binding support #95347

eric-ocasio-nxp · 2025-09-02T15:11:01Z

Add USB device binding for MCTP. Created new USB device class for MCTP, libMCTP binding, and sample application.

In order to support the USB binding for libMCTP, we must first add a device class for MCTP. MCTP is one of the base classes in the USB specification. Signed-off-by: Eric Ocasio <eric.ocasio@nxp.com>

Adds support for the USB device binding for MCTP. Binding created based on the DMTF specification for USB Transport Binding. The overall design of this binding follows the existing UART and I2C+GPIO bindings that already exist in Zephyr. This binding interacts with the new USBD_MCTP device class that is part of this PR. Signed-off-by: Eric Ocasio <eric.ocasio@nxp.com>

Based on the existing sample applications for MCTP, this new sample demonstrates how to use MCTP using the USB device binding. Signed-off-by: Eric Ocasio <eric.ocasio@nxp.com>

github-actions · 2025-09-02T15:11:47Z

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sonarqubecloud · 2025-09-02T15:14:52Z

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

henrikbrixandersen · 2025-09-17T06:59:44Z

doc/connectivity/usb/device_next/api/usbd_mctp.rst

@@ -0,0 +1,11 @@
+.. _usbd_mctp:
+
+MCTP USB device API


Please detail what "MCTP" actually is here.

teburd · 2025-09-17T13:41:08Z

samples/modules/pmci/mctp/usb_endpoint/CMakeLists.txt

+
+cmake_minimum_required(VERSION 3.20.0)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(mctp_endpoint)


project name could use something more descriptive, I get I'm guilty of probably starting this but perhaps mctp_usb_endpoint would be better

teburd · 2025-09-17T13:41:28Z

samples/modules/pmci/mctp/usb_endpoint/CMakeLists.txt

+project(mctp_endpoint)
+
+include(${ZEPHYR_BASE}/samples/subsys/usb/common/common.cmake)
+FILE(GLOB app_sources src/*.c)


please don't glob here

teburd · 2025-09-17T13:46:55Z

samples/modules/pmci/mctp/usb_endpoint/README.rst

+
+An example script to test this interface is provided below.
+
+.. code-block:: python


Honestly probably better to put this into scripts or into the sample directory itself as a python script with requirements.txt and all rather than pushing users to copy/paste, and figure out how to get the python deps installed.

Can always include whole code files into the docs like this with literalinclude

Sounds good. I moved it to a script within the sample folder with a requirements.txt and instructions in the README.

teburd · 2025-09-17T16:19:50Z

Non-blocking comments obviously, but would be good to see improvements.

jfischer-no · 2025-09-17T17:12:30Z

doc/connectivity/usb/device_next/api/index.rst

In order to support the USB binding for libMCTP, we must first add a device
class for MCTP. MCTP is one of the base classes in the USB specification.

Well no, it is specified by the "DMTF association", https://www.dmtf.org/sites/default/files/standards/documents/DSP0283_1.0.0.pdf

It's base class 0x14 in the USB spec, so I'm not sure what you mean here.

https://www.usb.org/defined-class-codes

jfischer-no · 2025-09-17T17:14:18Z

doc/connectivity/usb/device_next/usb_device.rst

 +-----------------------------------+-------------------------+-------------------------+
 | USB Video Class (UVC)             | Video device            | :samp:`uvc_{n}`         |
 +-----------------------------------+-------------------------+-------------------------+
+| USB MCTP over USB Endpoint        | :ref:`usbd_mctp`        | :samp:`mctp_{n}`        |


s/USB MCTP over USB Endpoint/MCTP over USB Binding

jfischer-no · 2025-09-17T17:16:27Z

doc/connectivity/usb/device_next/usb_device.rst


 * :zephyr:code-sample:`usb-hid-mouse`

+* :zephyr:code-sample:`mctp-usb-endpoint`


* :zephyr:code-sample:mctp-usb-binding`` Anyway, you cannot add it in this commit, this sample does not exist yet.

Do you suggest that I just update this file in a commit with the sample application, or do one 'super commit' with all of these feature/MCTP changes? I did it this way for human readability, but didn't fully understand the need for every commit to build.

"Commits in a pull request should represent clear, logical units of change that are easy to review and maintain bisectability." https://docs.zephyrproject.org/latest/contribute/contributor_expectations.html#pr-requirements

jfischer-no · 2025-09-17T17:17:53Z

include/zephyr/usb/class/usbd_mctp.h

+
+/**
+ * @file
+ * @brief USB MCTP over USB Protocol Endpoint Device Class (MCTP) public header


@brief MCTP over USB Binding implementation

jfischer-no · 2025-09-17T17:19:39Z

include/zephyr/usb/class/usbd_mctp.h

+ * @brief USB MCTP over USB Protocol Endpoint Device Class (MCTP) public header
+ *
+ * This header describes MCTP class interactions desgined to be used by libMCTP.
+ * The MCTP device itself is modelled with devicetree zephyr,mctp-usb compatible.


Not sure what that means, but usually devicetree is used to describe and instantiate a device. Whether it makes sense here or not is disputable.

jfischer-no · 2025-09-17T18:08:47Z

subsys/usb/device_next/class/usbd_mctp.c

+#include <zephyr/logging/log.h>
+LOG_MODULE_REGISTER(usbd_mctp, CONFIG_USBD_MCTP_LOG_LEVEL);
+
+#define DT_DRV_COMPAT zephyr_mctp_usb


Why do you thing it should model a device and use DT for instantiation. You do not have to follow usbd_hid approach. This looks more like a backend implementation, and for that you could provide hooks and instantiation macro, please take a look at new USB DFU device implementation.

I did it this way because there exists the possibility of having multiple MCTP buses/bindings. If the application requires more than one MCTP endpoint, a USB composite device could be used with more than one instance of USBD MCTP. Is there a way to accomplish this without DT?

jfischer-no · 2025-09-17T18:11:14Z

subsys/pmci/mctp/Kconfig


+config MCTP_USB
+	bool "MCTP USB Binding"
+	depends on USB_DEVICE_STACK_NEXT


redundant, USBD_MCTP_CLASS already depends on USB_DEVICE_STACK_NEXT.

jfischer-no · 2025-09-17T18:11:46Z

include/zephyr/pmci/mctp/mctp_usb.h

+			.name = STRINGIFY(_name), .version = 1,                                    \
+					  .pkt_size =                                              \
+						  MCTP_PACKET_SIZE(MCTP_USB_MAX_PACKET_LENGTH),    \
+					  .pkt_header = 0, .pkt_trailer = 0,                       \
+					  .start = mctp_usb_start, .tx = mctp_usb_tx,              \
+			},                                                                         \


Broken style.

jfischer-no · 2025-09-17T18:15:22Z

include/zephyr/pmci/mctp/mctp_usb.h

+ * @param _name Symbolic name of the bus binding variable
+ * @param _dev DeviceTree Node containing the configuration of this MCTP binding
+ */
+#define MCTP_USB_DT_DEFINE(_name, _dev)                                                            \


I do not get the purpose of this macro and the mctp_usb.c, you already have implemented instantiation and support for this function in the previous commit, what it that and why does it have to be divided?

I'm not following. This macro was created based on the other libmctp binding implementations. What do you mean by it being divided?

jfischer-no · 2025-09-17T18:18:40Z

samples/modules/pmci/mctp/usb_endpoint/Kconfig

@@ -0,0 +1,9 @@
+# Copyright (c) 2023 Nordic Semiconductor ASA


I am confused, is PMCI/MCTP not part of the Zephyr but an external module? If so then I do not think you can add any dependency on it to the USB subsystem.

The way I looked at it is that MCTP is called out as a base class on usb.org, so the device class implementation can exists in Zephyr, even if the higher-level MCTP protocol management comes from an external module. Right now it comes from libmctp (https://github.com/openbmc/libmctp).

I understand this concern. Is there something you think would create such a dependency? Again, I'm new to Zephyr, so maybe I don't fully understand something.

I am confused, is PMCI/MCTP not part of the Zephyr but an external module?

mctp is not an external module, it is part of the main manifest and there are dependencies on it already.

I am confused, is PMCI/MCTP not part of the Zephyr but an external module?

mctp is not an external module, it is part of the main manifest and there are dependencies on it already.

Anyway, the implementation cannot be part of subsys/usb, and has to go to the modules.

The fact that MCTP is listed on usb.org doesn't matter then?

@jfischer-no I too am confused by the comment that this should go to modules, mctp is a subsystem in zephyr built on libmctp.

@jfischer-no I too am confused by the comment that this should go to a modules, mctp is a subsystem in zephyr built on libmctp.

yeah, this is confusing. The fact that libmctp is a module is irrelevant, this is implementing usb bindings, using both mctp and usb in zephyr, this has nothing to do with libmctp, the usb binding is a zephyr thing.

The fact that MCTP is listed on usb.org doesn't matter then?

It does not mean anything. The specification is from DMTF association, and I already mentioned that, see #95347 (comment). You should know that, as you had to read it to write this code, or where does the code come from?

I too am confused by the comment that this should go to modules, mctp is a subsystem in zephyr built on libmctp.

What is external dependency, and like a sample in this PR is placed under sample/modules the implementation should be in modules/foobar.

yeah, this is confusing. The fact that libmctp is a module is irrelevant, this is implementing usb bindings, using both mctp and usb in zephyr, this has nothing to do with libmctp, the usb binding is a zephyr thing.

"usb binding" are useless without libmctp, "usb binding" is some trivial USB code that I will not accept in subsys/usb as long as there is no native libmctp implementation in Zephyr. And even then there is no need to place yet another backend to "something" in subsys/usb, a very good example is 6fddc44.

@jfischer-no please, this is like saying I should not accept any code that depends on a hal, we've passed that rubicon long ago

To say it should go in subsys/pmci/mctp that's fine, its where the rest of the binding code is anyways. I get if you don't want to take maintainership of this code that's very understandable and reasonable.

"usb binding" are useless without libmctp

right, but we have libmctp and it is not optional.

Anyways, what is it exactly that you want?

Is it about the location where the code should be hosted?

Is it about this base class not being defined by USB-IF? Where should those go? What about bluetooth, not defined by USB-IF yet it is hosted in subsys/usb/device/class?

Or is it about libmctp being a module? In this case, this is a library, mctp and bindings use this library, libmctp on its own does not do anything.

eric-ocasio-nxp added 3 commits September 2, 2025 09:16

usb: Add USB device class for base class MCTP Endpoint.

bc8e11a

In order to support the USB binding for libMCTP, we must first add a device class for MCTP. MCTP is one of the base classes in the USB specification. Signed-off-by: Eric Ocasio <eric.ocasio@nxp.com>

samples: Create MCTP over USB sample

8c07b95

Based on the existing sample applications for MCTP, this new sample demonstrates how to use MCTP using the USB device binding. Signed-off-by: Eric Ocasio <eric.ocasio@nxp.com>

zephyrbot added area: Devicetree area: USB Universal Serial Bus area: PMCI Platform Management Communications Infrastructure area: Samples Samples labels Sep 2, 2025

zephyrbot requested review from decsny, galak, JarmouniA, jfischer-no, kartben, KeHIntel, mbolivar, nashif, rruuaanng, teburd and tmon-nordic September 2, 2025 15:12

zephyrbot assigned teburd Sep 2, 2025

henrikbrixandersen reviewed Sep 17, 2025

View reviewed changes

teburd approved these changes Sep 17, 2025

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jfischer-no changed the title ~~Feature/add mctp usb binding~~ Add MCTP over USB Binding support Sep 17, 2025

jfischer-no requested changes Sep 17, 2025

View reviewed changes


		An example script to test this interface is provided below.

		.. code-block:: python


		* :zephyr:code-sample:`usb-hid-mouse`

		* :zephyr:code-sample:`mctp-usb-endpoint`

		@@ -0,0 +1,9 @@
		# Copyright (c) 2023 Nordic Semiconductor ASA

Add MCTP over USB Binding support #95347

Are you sure you want to change the base?

Add MCTP over USB Binding support #95347

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eric-ocasio-nxp commented Sep 2, 2025 •

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