samples: pmci: mctp: Add i2c+gpio endpoint sample

Adds sample showing i2c+gpio endpoint bindings in use.

Provides an overlay for the frdm-mcxn947 development board using JP8
pins for i2c and gpio connectivity.

The sample periodically sends a "ping" message to the bus controller and
prints out any messages it receives itself.

Signed-off-by: Tom Burdick <thomas.burdick@intel.com>

samples/modules/pmci/mctp/i2c_gpio_bus_endpoint/CMakeLists.txt

@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(mctp_i2c_gpio_bus_endpoint)
+
+target_sources(app PRIVATE src/main.c)

samples/modules/pmci/mctp/i2c_gpio_bus_endpoint/README.rst

@@ -0,0 +1,32 @@
+.. zephyr:code-sample:: mctp_i2c_bus_endpoint
+   :name: MCTP I2C GPIO Endpoint Node Sample
+
+   Create an MCTP endpoint node controlling I2C with GPIO signaling.
+
+Overview
+********
+Sets up an MCTP endpoint node that may talk to a top node and peer to other MCTP endpoints.
+
+Requirements
+************
+Board with an I2C and a GPIO used for signaling the top node to read the target device.
+
+Wiring
+******
+A common I2C bus SDA/SCL pair connected to any number of boards (setup in devicetree)
+along with a GPIO for signaling endpoint write requests.
+
+Building and Running
+********************
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/modules/pmci/mctp/i2c_gpio_bus_endpoint
+   :host-os: unix
+   :board: frdm_mcxn947_mcxn947_cpu0
+   :goals: run
+   :compact:
+
+References
+**********
+
+`MCTP Base Specification 2019 <https://www.dmtf.org/sites/default/files/standards/documents/DSP0236_1.3.1.pdf>`_

samples/modules/pmci/mctp/i2c_gpio_bus_endpoint/boards/frdm_mcxn947_mcxn947_cpu0.overlay

@@ -0,0 +1,36 @@
+#include <zephyr/dt-bindings/gpio/gpio.h>
+
+/* Sets up I2C and a GPIO on JP8 to use as our i2c bus for MCTP */
+
+
+&nxp_lcd_8080_connector {
+	status = "disabled";
+};
+
+&flexio0 {
+	status = "disabled";
+};
+
+&gpio0 {
+	status = "okay";
+};
+
+&flexcomm2 {
+	status = "okay";
+};
+
+&flexcomm2_lpi2c2 {
+	status = "okay";
+	clock-frequency = <I2C_BITRATE_STANDARD>;
+};
+
+
+/ {
+	mctp_i2c: mctp_i2c {
+		compatible = "zephyr,mctp-i2c-gpio-target";
+		i2c = <&flexcomm2_lpi2c2>;
+		i2c-addr = <70>;
+		endpoint-id = <11>;
+		endpoint-gpios = <&gpio0 7 GPIO_ACTIVE_HIGH>;
+	};
+};

samples/modules/pmci/mctp/i2c_gpio_bus_endpoint/prj.conf

@@ -0,0 +1,8 @@
+CONFIG_I2C=y
+CONFIG_I2C_TARGET=y
+CONFIG_MCTP=y
+CONFIG_MCTP_I2C_GPIO_TARGET=y
+CONFIG_MCTP_LOG_LEVEL_DBG=y
+CONFIG_LOG=y
+#CONFIG_LOG_MODE_IMMEDIATE=y
+CONFIG_LOG_BUFFER_SIZE=4096

samples/modules/pmci/mctp/i2c_gpio_bus_endpoint/src/main.c

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2025 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <assert.h>
+#include <unistd.h>
+#include <zephyr/types.h>
+#include <zephyr/kernel.h>
+#include <libmctp.h>
+#include <zephyr/pmci/mctp/mctp_i2c_gpio_target.h>
+
+#include <zephyr/logging/log.h>
+LOG_MODULE_REGISTER(mctp_i2c_gpio_bus_endpoint);
+
+MCTP_I2C_GPIO_TARGET_DT_DEFINE(mctp_i2c_ctrl, DT_NODELABEL(mctp_i2c));
+
+static void rx_message(uint8_t eid, bool tag_owner, uint8_t msg_tag, void *data, void *msg,
+		       size_t len)
+{
+	LOG_INF("received message \"%s\" from endpoint %d, msg_tag %d, len %zu", (char *)msg, eid,
+		msg_tag, len);
+}
+
+#define BUS_OWNER_ID 20
+
+int main(void)
+{
+	int rc;
+	struct mctp *mctp_ctx;
+
+	LOG_INF("MCTP Host EID:%d on %s\n", mctp_i2c_ctrl.endpoint_id, CONFIG_BOARD_TARGET);
+
+	mctp_ctx = mctp_init();
+	__ASSERT_NO_MSG(mctp_ctx != NULL);
+	mctp_register_bus(mctp_ctx, &mctp_i2c_ctrl.binding, mctp_i2c_ctrl.endpoint_id);
+	mctp_set_rx_all(mctp_ctx, rx_message, NULL);
+
+	/*
+	 * 1. MCTP poll loop, send "ping" to each endpoint and get "pong" back
+	 * 2. Then send a broadcast "hello" to each endpoint and get a "from endoint %d" back
+	 */
+	while (true) {
+		rc = mctp_message_tx(mctp_ctx, BUS_OWNER_ID, false,
+				0, "ping", sizeof("ping"));
+		if (rc != 0) {
+			LOG_WRN("Failed to send message \"ping\", errno %d\n", rc);
+		}
+		k_msleep(500);
+	}
+
+	return 0;
+}