subsys/ipc/ipc_service/backends/ipc_icmsg_me_follower.c - third_party/github/zephyrproject-rtos/zephyr - Git at Google

 /*
  * Copyright (c) 2022 Nordic Semiconductor ASA
  *
  * SPDX-License-Identifier: Apache-2.0
  */

 #include <string.h>

 #include <zephyr/device.h>
 #include <zephyr/ipc/icmsg.h>
 #include <zephyr/ipc/ipc_service_backend.h>

 #define DT_DRV_COMPAT	zephyr_ipc_icmsg_me_follower

 #define INVALID_EPT_ID 255
 #define SEND_BUF_SIZE CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_SEND_BUF_SIZE
 #define NUM_EP        CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_NUM_EP
 #define EP_NAME_LEN   CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_EP_NAME_LEN

 #define EVENT_BOUND 0x01

 /* If more bytes than 1 was used for endpoint id, endianness should be
  * considered.
  */
 typedef uint8_t ept_id_t;

 struct ept_disc_rmt_cache_t {
 	ept_id_t id;
 	char name[EP_NAME_LEN];
 };

 struct backend_data_t {
 	struct icmsg_data_t icmsg_data;
 	struct ipc_ept_cfg ept_cfg;

 	struct k_event event;

 	struct k_mutex epts_mutex;
 	struct k_mutex send_mutex;
 	const struct ipc_ept_cfg *epts[NUM_EP];

 	const struct ipc_ept_cfg *ept_disc_loc_cache[NUM_EP];
 	struct ept_disc_rmt_cache_t ept_disc_rmt_cache[NUM_EP];

 	uint8_t send_buffer[SEND_BUF_SIZE] __aligned(4);
 };

 static const struct ipc_ept_cfg *get_ept_cached_loc(
 		const struct backend_data_t *data, const char *name, size_t len)
 {
 	for (int i = 0; i < NUM_EP; i++) {
 		if (data->ept_disc_loc_cache[i] == NULL) {
 			continue;
 		}
 		if (strncmp(data->ept_disc_loc_cache[i]->name, name,
 				MIN(EP_NAME_LEN, len)) == 0) {
 			return data->ept_disc_loc_cache[i];
 		}
 	}

 	return NULL;
 }

 static struct ept_disc_rmt_cache_t *get_ept_cached_rmt(
 		struct backend_data_t *data, const char *name, size_t len)
 {
 	size_t cmp_len = MIN(EP_NAME_LEN, len);

 	for (int i = 0; i < NUM_EP; i++) {
 		if (strncmp(data->ept_disc_rmt_cache[i].name, name,
 				cmp_len) == 0 &&
 		    strlen(data->ept_disc_rmt_cache[i].name) == len) {
 			return &data->ept_disc_rmt_cache[i];
 		}
 	}

 	return NULL;
 }

 static int cache_ept_loc(struct backend_data_t *data, const struct ipc_ept_cfg *ept)
 {
 	for (int i = 0; i < NUM_EP; i++) {
 		if (data->ept_disc_loc_cache[i] == NULL) {
 			data->ept_disc_loc_cache[i] = ept;
 			return 0;
 		}
 	}

 	return -ENOMEM;
 }

 static int cache_ept_rmt(struct backend_data_t *data, const char *name,
 			 size_t len, ept_id_t id)
 {
 	for (int i = 0; i < NUM_EP; i++) {
 		if (!strlen(data->ept_disc_rmt_cache[i].name)) {
 			size_t copy_len = MIN(EP_NAME_LEN - 1, len);

 			strncpy(data->ept_disc_rmt_cache[i].name, name,
 					copy_len);
 			data->ept_disc_rmt_cache[i].name[copy_len] = '\0';
 			data->ept_disc_rmt_cache[i].id = id;
 			return 0;
 		}
 	}

 	return -ENOMEM;
 }

 static void *icmsg_buffer_to_user_buffer(const void *icmsg_buffer)
 {
 	return (void *)(((char *)icmsg_buffer) + sizeof(ept_id_t));
 }

 static void *user_buffer_to_icmsg_buffer(const void *user_buffer)
 {
 	return (void *)(((char *)user_buffer) - sizeof(ept_id_t));
 }

 static size_t icmsg_buffer_len_to_user_buffer_len(size_t icmsg_buffer_len)
 {
 	return icmsg_buffer_len - sizeof(ept_id_t);
 }

 static size_t user_buffer_len_to_icmsg_buffer_len(size_t user_buffer_len)
 {
 	return user_buffer_len + sizeof(ept_id_t);
 }

 static void set_ept_id_in_send_buffer(uint8_t *send_buffer, ept_id_t ept_id)
 {
 	send_buffer[0] = ept_id;
 }

 static int bind_ept(const struct icmsg_config_t *conf,
 		struct backend_data_t *data, const struct ipc_ept_cfg *ept,
 		ept_id_t id)
 {
 	__ASSERT_NO_MSG(id <= NUM_EP);

 	int r;
 	int i = id - 1;
 	const uint8_t confirmation[] = {
 		0,  /* EP discovery endpoint id */
 		id, /* Bound endpoint id */
 	};

 	data->epts[i] = ept;

 	k_event_wait(&data->event, EVENT_BOUND, false, K_FOREVER);
 	r = icmsg_send(conf, &data->icmsg_data, confirmation,
 		       sizeof(confirmation));
 	if (r < 0) {
 		return r;
 	}

 	if (ept->cb.bound) {
 		ept->cb.bound(ept->priv);
 	}

 	return 0;
 }

 static void bound(void *priv)
 {
 	const struct device *instance = priv;
 	struct backend_data_t *dev_data = instance->data;

 	k_event_post(&dev_data->event, EVENT_BOUND);
 }

 static void received(const void *data, size_t len, void *priv)
 {
 	const struct device *instance = priv;
 	const struct icmsg_config_t *conf = instance->config;
 	struct backend_data_t *dev_data = instance->data;

 	const ept_id_t *id = data;

 	__ASSERT_NO_MSG(len > 0);

 	if (*id == 0) {
 		__ASSERT_NO_MSG(len > 1);

 		id++;
 		ept_id_t ept_id = *id;
 		const char *name = id + 1;
 		size_t name_len = len - 2 * sizeof(ept_id_t);

 		k_mutex_lock(&dev_data->epts_mutex, K_FOREVER);

 		const struct ipc_ept_cfg *ept =
 				get_ept_cached_loc(dev_data, name, name_len);
 		if (ept == NULL) {
 			cache_ept_rmt(dev_data, name, name_len, ept_id);
 		} else {
 			/* Remote cache entry should be already filled during
 			 * the local cache entry registration. Update its
 			 * id for correct token value.
 			 */
 			struct ept_disc_rmt_cache_t *rmt_cache_entry;

 			rmt_cache_entry = get_ept_cached_rmt(dev_data, name,
 							     name_len);

 			__ASSERT_NO_MSG(rmt_cache_entry != NULL);
 			__ASSERT_NO_MSG(rmt_cache_entry->id == INVALID_EPT_ID);
 			rmt_cache_entry->id = ept_id;

 			bind_ept(conf, dev_data, ept, ept_id);
 		}

 		k_mutex_unlock(&dev_data->epts_mutex);
 	} else {
 		int i = *id - 1;

 		if (i >= NUM_EP) {
 			return;
 		}
 		if (dev_data->epts[i] == NULL) {
 			return;
 		}
 		if (dev_data->epts[i]->cb.received) {
 			dev_data->epts[i]->cb.received(
 				icmsg_buffer_to_user_buffer(data),
 				icmsg_buffer_len_to_user_buffer_len(len),
 				dev_data->epts[i]->priv);
 		}
 	}
 }

 static const struct ipc_service_cb cb = {
 	.bound = bound,
 	.received = received,
 	.error = NULL,
 };

 static int open(const struct device *instance)
 {
 	const struct icmsg_config_t *conf = instance->config;
 	struct backend_data_t *dev_data = instance->data;

 	dev_data->ept_cfg.cb = cb;
 	dev_data->ept_cfg.priv = (void *)instance;

 	return icmsg_open(conf, &dev_data->icmsg_data, &dev_data->ept_cfg.cb,
 		dev_data->ept_cfg.priv);
 }

 static int register_ept(const struct device *instance, void **token,
 			const struct ipc_ept_cfg *cfg)
 {
 	const struct icmsg_config_t *conf = instance->config;
 	struct backend_data_t *data = instance->data;
 	struct ept_disc_rmt_cache_t *rmt_cache_entry;
 	int r;

 	k_mutex_lock(&data->epts_mutex, K_FOREVER);

 	rmt_cache_entry = get_ept_cached_rmt(data, cfg->name,
 					     strlen(cfg->name));
 	if (rmt_cache_entry == NULL) {
 		r = cache_ept_loc(data, cfg);
 		if (r) {
 			goto exit;
 		}

 		/* Register remote cache entry alongside the local one to
 		 * make available endpoint id storage required for token.
 		 */
 		r = cache_ept_rmt(data, cfg->name, strlen(cfg->name),
 				INVALID_EPT_ID);
 		if (r) {
 			goto exit;
 		}

 		rmt_cache_entry = get_ept_cached_rmt(data, cfg->name,
 						     strlen(cfg->name));
 		__ASSERT_NO_MSG(rmt_cache_entry != NULL);
 		*token = &rmt_cache_entry->id;
 	} else {
 		ept_id_t ept_id = rmt_cache_entry->id;

 		if (ept_id == INVALID_EPT_ID) {
 			r = -EAGAIN;
 			goto exit;
 		}

 		*token = &rmt_cache_entry->id;
 		r = bind_ept(conf, data, cfg, ept_id);
 	}

 exit:
 	k_mutex_unlock(&data->epts_mutex);
 	return r;
 }

 static int send(const struct device *instance, void *token,
 		const void *msg, size_t user_len)
 {
 	const struct icmsg_config_t *conf = instance->config;
 	struct backend_data_t *dev_data = instance->data;
 	ept_id_t *id = token;
 	int r;
 	int sent_bytes;

 	if (*id == INVALID_EPT_ID) {
 		return -ENOTCONN;
 	}

 	if (user_len >= SEND_BUF_SIZE - sizeof(ept_id_t)) {
 		return -EBADMSG;
 	}

 	k_mutex_lock(&dev_data->send_mutex, K_FOREVER);

 	/* TODO: Optimization: How to avoid this copying? */
 	/* Scatter list supported by icmsg? */
 	set_ept_id_in_send_buffer(dev_data->send_buffer, *id);
 	memcpy(icmsg_buffer_to_user_buffer(dev_data->send_buffer), msg,
 			user_len);

 	r = icmsg_send(conf, &dev_data->icmsg_data, dev_data->send_buffer,
 			user_buffer_len_to_icmsg_buffer_len(user_len));

 	if (r > 0) {
 		sent_bytes = r - 1;
 	}

 	k_mutex_unlock(&dev_data->send_mutex);

 	if (r > 0) {
 		return sent_bytes;
 	} else {
 		return r;
 	}
 }

 static size_t get_buffer_length_to_pass(size_t allocated_buffer_length)
 {
 	if (allocated_buffer_length >= sizeof(ept_id_t)) {
 		return icmsg_buffer_len_to_user_buffer_len(
 				allocated_buffer_length);
 	} else {
 		return 0;
 	}
 }

 static int get_tx_buffer(const struct device *instance, void *token,
 			 void **data, uint32_t *user_len, k_timeout_t wait)
 {
 	const struct icmsg_config_t *conf = instance->config;
 	struct backend_data_t *dev_data = instance->data;
 	void *icmsg_buffer;
 	int r;
 	size_t icmsg_len;

 	if (!K_TIMEOUT_EQ(wait, K_NO_WAIT)) {
 		return -ENOTSUP;
 	}

 	if (*user_len) {
 		icmsg_len = user_buffer_len_to_icmsg_buffer_len(*user_len);
 	} else {
 		icmsg_len = 0;
 	}

 	r = icmsg_get_tx_buffer(conf, &dev_data->icmsg_data, &icmsg_buffer,
 				&icmsg_len);
 	if (r == -ENOMEM) {
 		*user_len = get_buffer_length_to_pass(icmsg_len);
 		return -ENOMEM;
 	}

 	if (r < 0) {
 		return r;
 	}

 	*user_len = get_buffer_length_to_pass(icmsg_len);
 	/* If requested max buffer length (*user_len == 0) allocated buffer
 	 * might be shorter than sizeof(ept_id_t). In such circumstances drop
 	 * the buffer and return error.
 	 */

 	if (*user_len) {
 		*data = icmsg_buffer_to_user_buffer(icmsg_buffer);
 		return 0;
 	}

 	r = icmsg_drop_tx_buffer(conf, &dev_data->icmsg_data,
 				 icmsg_buffer);
 	__ASSERT_NO_MSG(!r);
 	return -ENOBUFS;
 }

 static int drop_tx_buffer(const struct device *instance, void *token,
 			  const void *data)
 {
 	const struct icmsg_config_t *conf = instance->config;
 	struct backend_data_t *dev_data = instance->data;
 	const void *buffer_to_drop = user_buffer_to_icmsg_buffer(data);

 	return icmsg_drop_tx_buffer(conf, &dev_data->icmsg_data, buffer_to_drop);
 }

 static int send_nocopy(const struct device *instance, void *token,
 			const void *data, size_t len)
 {
 	const struct icmsg_config_t *conf = instance->config;
 	struct backend_data_t *dev_data = instance->data;
 	ept_id_t *id = token;
 	void *buffer_to_send;
 	size_t len_to_send;
 	int r;

 	if (*id == INVALID_EPT_ID) {
 		return -ENOTCONN;
 	}

 	buffer_to_send = user_buffer_to_icmsg_buffer(data);
 	len_to_send = user_buffer_len_to_icmsg_buffer_len(len);

 	set_ept_id_in_send_buffer(buffer_to_send, *id);

 	r = icmsg_send_nocopy(conf, &dev_data->icmsg_data, buffer_to_send,
 			      len_to_send);
 	if (r > 0) {
 		return icmsg_buffer_len_to_user_buffer_len(r);
 	} else {
 		return r;
 	}
 }

 #ifdef CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_NOCOPY_RX
 int hold_rx_buffer(const struct device *instance, void *token, void *data)
 {
 	const struct icmsg_config_t *conf = instance->config;
 	struct backend_data_t *dev_data = instance->data;
 	void *icmsg_buffer = user_buffer_to_icmsg_buffer(data);

 	return icmsg_hold_rx_buffer(conf, &dev_data->icmsg_data, icmsg_buffer);
 }

 int release_rx_buffer(const struct device *instance, void *token, void *data)
 {
 	const struct icmsg_config_t *conf = instance->config;
 	struct backend_data_t *dev_data = instance->data;
 	void *icmsg_buffer = user_buffer_to_icmsg_buffer(data);

 	return icmsg_release_rx_buffer(conf, &dev_data->icmsg_data,
 			icmsg_buffer);
 }
 #endif /* CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_NOCOPY_RX */

 const static struct ipc_service_backend backend_ops = {
 	.open_instance = open,
 	.register_endpoint = register_ept,
 	.send = send,

 	.get_tx_buffer = get_tx_buffer,
 	.drop_tx_buffer = drop_tx_buffer,
 	.send_nocopy = send_nocopy,

 #ifdef CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_NOCOPY_RX
 	.hold_rx_buffer = hold_rx_buffer,
 	.release_rx_buffer = release_rx_buffer,
 #endif
 };

 static int backend_init(const struct device *instance)
 {
 	const struct icmsg_config_t *conf = instance->config;
 	struct backend_data_t *dev_data = instance->data;

 	k_event_init(&dev_data->event);
 	k_mutex_init(&dev_data->epts_mutex);
 	k_mutex_init(&dev_data->send_mutex);

 	return icmsg_init(conf, &dev_data->icmsg_data);
 }

 #define BACKEND_CONFIG_POPULATE(i)						\
 	{									\
 		.tx_shm_size = DT_REG_SIZE(DT_INST_PHANDLE(i, tx_region)),	\
 		.tx_shm_addr = DT_REG_ADDR(DT_INST_PHANDLE(i, tx_region)),	\
 		.rx_shm_size = DT_REG_SIZE(DT_INST_PHANDLE(i, rx_region)),	\
 		.rx_shm_addr = DT_REG_ADDR(DT_INST_PHANDLE(i, rx_region)),	\
 		.mbox_tx = MBOX_DT_CHANNEL_GET(DT_DRV_INST(i), tx),		\
 		.mbox_rx = MBOX_DT_CHANNEL_GET(DT_DRV_INST(i), rx),		\
 	}

 #define DEFINE_BACKEND_DEVICE(i)						\
 	static const struct icmsg_config_t backend_config_##i =			\
 		BACKEND_CONFIG_POPULATE(i);					\
 	static struct backend_data_t backend_data_##i;				\
 										\
 	DEVICE_DT_INST_DEFINE(i,						\
 			 &backend_init,						\
 			 NULL,							\
 			 &backend_data_##i,					\
 			 &backend_config_##i,					\
 			 POST_KERNEL,						\
 			 CONFIG_IPC_SERVICE_REG_BACKEND_PRIORITY,		\
 			 &backend_ops);

 DT_INST_FOREACH_STATUS_OKAY(DEFINE_BACKEND_DEVICE)

 #if defined(CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_SHMEM_RESET)
 #define BACKEND_CONFIG_DEFINE(i) BACKEND_CONFIG_POPULATE(i),
 static int shared_memory_prepare(const struct device *arg)
 {
 	const struct icmsg_config_t *backend_config;
 	const struct icmsg_config_t backend_configs[] = {
 		DT_INST_FOREACH_STATUS_OKAY(BACKEND_CONFIG_DEFINE)
 	};

 	for (backend_config = backend_configs;
 	     backend_config < backend_configs + ARRAY_SIZE(backend_configs);
 	     backend_config++) {
 		icmsg_clear_tx_memory(backend_config);
 		icmsg_clear_rx_memory(backend_config);
 	}

 	return 0;
 }

 SYS_INIT(shared_memory_prepare, PRE_KERNEL_1, 1);
 #endif /* CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_SHMEM_RESET */
	/*
	* Copyright (c) 2022 Nordic Semiconductor ASA
	*
	* SPDX-License-Identifier: Apache-2.0
	*/

	#include <string.h>

	#include <zephyr/device.h>
	#include <zephyr/ipc/icmsg.h>
	#include <zephyr/ipc/ipc_service_backend.h>

	#define DT_DRV_COMPAT zephyr_ipc_icmsg_me_follower

	#define INVALID_EPT_ID 255
	#define SEND_BUF_SIZE CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_SEND_BUF_SIZE
	#define NUM_EP CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_NUM_EP
	#define EP_NAME_LEN CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_EP_NAME_LEN

	#define EVENT_BOUND 0x01

	/* If more bytes than 1 was used for endpoint id, endianness should be
	* considered.
	*/
	typedef uint8_t ept_id_t;

	struct ept_disc_rmt_cache_t {
	ept_id_t id;
	char name[EP_NAME_LEN];
	};

	struct backend_data_t {
	struct icmsg_data_t icmsg_data;
	struct ipc_ept_cfg ept_cfg;

	struct k_event event;

	struct k_mutex epts_mutex;
	struct k_mutex send_mutex;
	const struct ipc_ept_cfg *epts[NUM_EP];

	const struct ipc_ept_cfg *ept_disc_loc_cache[NUM_EP];
	struct ept_disc_rmt_cache_t ept_disc_rmt_cache[NUM_EP];

	uint8_t send_buffer[SEND_BUF_SIZE] __aligned(4);
	};

	static const struct ipc_ept_cfg *get_ept_cached_loc(
	const struct backend_data_t data, const char name, size_t len)
	{
	for (int i = 0; i < NUM_EP; i++) {
	if (data->ept_disc_loc_cache[i] == NULL) {
	continue;
	}
	if (strncmp(data->ept_disc_loc_cache[i]->name, name,
	MIN(EP_NAME_LEN, len)) == 0) {
	return data->ept_disc_loc_cache[i];
	}
	}

	return NULL;
	}

	static struct ept_disc_rmt_cache_t *get_ept_cached_rmt(
	struct backend_data_t data, const char name, size_t len)
	{
	size_t cmp_len = MIN(EP_NAME_LEN, len);

	for (int i = 0; i < NUM_EP; i++) {
	if (strncmp(data->ept_disc_rmt_cache[i].name, name,
	cmp_len) == 0 &&
	strlen(data->ept_disc_rmt_cache[i].name) == len) {
	return &data->ept_disc_rmt_cache[i];
	}
	}

	return NULL;
	}

	static int cache_ept_loc(struct backend_data_t data, const struct ipc_ept_cfg ept)
	{
	for (int i = 0; i < NUM_EP; i++) {
	if (data->ept_disc_loc_cache[i] == NULL) {
	data->ept_disc_loc_cache[i] = ept;
	return 0;
	}
	}

	return -ENOMEM;
	}

	static int cache_ept_rmt(struct backend_data_t data, const char name,
	size_t len, ept_id_t id)
	{
	for (int i = 0; i < NUM_EP; i++) {
	if (!strlen(data->ept_disc_rmt_cache[i].name)) {
	size_t copy_len = MIN(EP_NAME_LEN - 1, len);

	strncpy(data->ept_disc_rmt_cache[i].name, name,
	copy_len);
	data->ept_disc_rmt_cache[i].name[copy_len] = '\0';
	data->ept_disc_rmt_cache[i].id = id;
	return 0;
	}
	}

	return -ENOMEM;
	}

	static void icmsg_buffer_to_user_buffer(const void icmsg_buffer)
	{
	return (void )(((char )icmsg_buffer) + sizeof(ept_id_t));
	}

	static void user_buffer_to_icmsg_buffer(const void user_buffer)
	{
	return (void )(((char )user_buffer) - sizeof(ept_id_t));
	}

	static size_t icmsg_buffer_len_to_user_buffer_len(size_t icmsg_buffer_len)
	{
	return icmsg_buffer_len - sizeof(ept_id_t);
	}

	static size_t user_buffer_len_to_icmsg_buffer_len(size_t user_buffer_len)
	{
	return user_buffer_len + sizeof(ept_id_t);
	}

	static void set_ept_id_in_send_buffer(uint8_t *send_buffer, ept_id_t ept_id)
	{
	send_buffer[0] = ept_id;
	}

	static int bind_ept(const struct icmsg_config_t *conf,
	struct backend_data_t data, const struct ipc_ept_cfg ept,
	ept_id_t id)
	{
	__ASSERT_NO_MSG(id <= NUM_EP);

	int r;
	int i = id - 1;
	const uint8_t confirmation[] = {
	0, /* EP discovery endpoint id */
	id, /* Bound endpoint id */
	};

	data->epts[i] = ept;

	k_event_wait(&data->event, EVENT_BOUND, false, K_FOREVER);
	r = icmsg_send(conf, &data->icmsg_data, confirmation,
	sizeof(confirmation));
	if (r < 0) {
	return r;
	}

	if (ept->cb.bound) {
	ept->cb.bound(ept->priv);
	}

	return 0;
	}

	static void bound(void *priv)
	{
	const struct device *instance = priv;
	struct backend_data_t *dev_data = instance->data;

	k_event_post(&dev_data->event, EVENT_BOUND);
	}

	static void received(const void data, size_t len, void priv)
	{
	const struct device *instance = priv;
	const struct icmsg_config_t *conf = instance->config;
	struct backend_data_t *dev_data = instance->data;

	const ept_id_t *id = data;

	__ASSERT_NO_MSG(len > 0);

	if (*id == 0) {
	__ASSERT_NO_MSG(len > 1);

	id++;
	ept_id_t ept_id = *id;
	const char *name = id + 1;
	size_t name_len = len - 2 * sizeof(ept_id_t);

	k_mutex_lock(&dev_data->epts_mutex, K_FOREVER);

	const struct ipc_ept_cfg *ept =
	get_ept_cached_loc(dev_data, name, name_len);
	if (ept == NULL) {
	cache_ept_rmt(dev_data, name, name_len, ept_id);
	} else {
	/* Remote cache entry should be already filled during
	* the local cache entry registration. Update its
	* id for correct token value.
	*/
	struct ept_disc_rmt_cache_t *rmt_cache_entry;

	rmt_cache_entry = get_ept_cached_rmt(dev_data, name,
	name_len);

	__ASSERT_NO_MSG(rmt_cache_entry != NULL);
	__ASSERT_NO_MSG(rmt_cache_entry->id == INVALID_EPT_ID);
	rmt_cache_entry->id = ept_id;

	bind_ept(conf, dev_data, ept, ept_id);
	}

	k_mutex_unlock(&dev_data->epts_mutex);
	} else {
	int i = *id - 1;

	if (i >= NUM_EP) {
	return;
	}
	if (dev_data->epts[i] == NULL) {
	return;
	}
	if (dev_data->epts[i]->cb.received) {
	dev_data->epts[i]->cb.received(
	icmsg_buffer_to_user_buffer(data),
	icmsg_buffer_len_to_user_buffer_len(len),
	dev_data->epts[i]->priv);
	}
	}
	}

	static const struct ipc_service_cb cb = {
	.bound = bound,
	.received = received,
	.error = NULL,
	};

	static int open(const struct device *instance)
	{
	const struct icmsg_config_t *conf = instance->config;
	struct backend_data_t *dev_data = instance->data;

	dev_data->ept_cfg.cb = cb;
	dev_data->ept_cfg.priv = (void *)instance;

	return icmsg_open(conf, &dev_data->icmsg_data, &dev_data->ept_cfg.cb,
	dev_data->ept_cfg.priv);
	}

	static int register_ept(const struct device instance, void *token,
	const struct ipc_ept_cfg *cfg)
	{
	const struct icmsg_config_t *conf = instance->config;
	struct backend_data_t *data = instance->data;
	struct ept_disc_rmt_cache_t *rmt_cache_entry;
	int r;

	k_mutex_lock(&data->epts_mutex, K_FOREVER);

	rmt_cache_entry = get_ept_cached_rmt(data, cfg->name,
	strlen(cfg->name));
	if (rmt_cache_entry == NULL) {
	r = cache_ept_loc(data, cfg);
	if (r) {
	goto exit;
	}

	/* Register remote cache entry alongside the local one to
	* make available endpoint id storage required for token.
	*/
	r = cache_ept_rmt(data, cfg->name, strlen(cfg->name),
	INVALID_EPT_ID);
	if (r) {
	goto exit;
	}

	rmt_cache_entry = get_ept_cached_rmt(data, cfg->name,
	strlen(cfg->name));
	__ASSERT_NO_MSG(rmt_cache_entry != NULL);
	*token = &rmt_cache_entry->id;
	} else {
	ept_id_t ept_id = rmt_cache_entry->id;

	if (ept_id == INVALID_EPT_ID) {
	r = -EAGAIN;
	goto exit;
	}

	*token = &rmt_cache_entry->id;
	r = bind_ept(conf, data, cfg, ept_id);
	}

	exit:
	k_mutex_unlock(&data->epts_mutex);
	return r;
	}

	static int send(const struct device instance, void token,
	const void *msg, size_t user_len)
	{
	const struct icmsg_config_t *conf = instance->config;
	struct backend_data_t *dev_data = instance->data;
	ept_id_t *id = token;
	int r;
	int sent_bytes;

	if (*id == INVALID_EPT_ID) {
	return -ENOTCONN;
	}

	if (user_len >= SEND_BUF_SIZE - sizeof(ept_id_t)) {
	return -EBADMSG;
	}

	k_mutex_lock(&dev_data->send_mutex, K_FOREVER);

	/* TODO: Optimization: How to avoid this copying? */
	/* Scatter list supported by icmsg? */
	set_ept_id_in_send_buffer(dev_data->send_buffer, *id);
	memcpy(icmsg_buffer_to_user_buffer(dev_data->send_buffer), msg,
	user_len);

	r = icmsg_send(conf, &dev_data->icmsg_data, dev_data->send_buffer,
	user_buffer_len_to_icmsg_buffer_len(user_len));

	if (r > 0) {
	sent_bytes = r - 1;
	}

	k_mutex_unlock(&dev_data->send_mutex);

	if (r > 0) {
	return sent_bytes;
	} else {
	return r;
	}
	}

	static size_t get_buffer_length_to_pass(size_t allocated_buffer_length)
	{
	if (allocated_buffer_length >= sizeof(ept_id_t)) {
	return icmsg_buffer_len_to_user_buffer_len(
	allocated_buffer_length);
	} else {
	return 0;
	}
	}

	static int get_tx_buffer(const struct device instance, void token,
	void *data, uint32_t user_len, k_timeout_t wait)
	{
	const struct icmsg_config_t *conf = instance->config;
	struct backend_data_t *dev_data = instance->data;
	void *icmsg_buffer;
	int r;
	size_t icmsg_len;

	if (!K_TIMEOUT_EQ(wait, K_NO_WAIT)) {
	return -ENOTSUP;
	}

	if (*user_len) {
	icmsg_len = user_buffer_len_to_icmsg_buffer_len(*user_len);
	} else {
	icmsg_len = 0;
	}

	r = icmsg_get_tx_buffer(conf, &dev_data->icmsg_data, &icmsg_buffer,
	&icmsg_len);
	if (r == -ENOMEM) {
	*user_len = get_buffer_length_to_pass(icmsg_len);
	return -ENOMEM;
	}

	if (r < 0) {
	return r;
	}

	*user_len = get_buffer_length_to_pass(icmsg_len);
	/* If requested max buffer length (*user_len == 0) allocated buffer
	* might be shorter than sizeof(ept_id_t). In such circumstances drop
	* the buffer and return error.
	*/

	if (*user_len) {
	*data = icmsg_buffer_to_user_buffer(icmsg_buffer);
	return 0;
	}

	r = icmsg_drop_tx_buffer(conf, &dev_data->icmsg_data,
	icmsg_buffer);
	__ASSERT_NO_MSG(!r);
	return -ENOBUFS;
	}

	static int drop_tx_buffer(const struct device instance, void token,
	const void *data)
	{
	const struct icmsg_config_t *conf = instance->config;
	struct backend_data_t *dev_data = instance->data;
	const void *buffer_to_drop = user_buffer_to_icmsg_buffer(data);

	return icmsg_drop_tx_buffer(conf, &dev_data->icmsg_data, buffer_to_drop);
	}

	static int send_nocopy(const struct device instance, void token,
	const void *data, size_t len)
	{
	const struct icmsg_config_t *conf = instance->config;
	struct backend_data_t *dev_data = instance->data;
	ept_id_t *id = token;
	void *buffer_to_send;
	size_t len_to_send;
	int r;

	if (*id == INVALID_EPT_ID) {
	return -ENOTCONN;
	}

	buffer_to_send = user_buffer_to_icmsg_buffer(data);
	len_to_send = user_buffer_len_to_icmsg_buffer_len(len);

	set_ept_id_in_send_buffer(buffer_to_send, *id);

	r = icmsg_send_nocopy(conf, &dev_data->icmsg_data, buffer_to_send,
	len_to_send);
	if (r > 0) {
	return icmsg_buffer_len_to_user_buffer_len(r);
	} else {
	return r;
	}
	}

	#ifdef CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_NOCOPY_RX
	int hold_rx_buffer(const struct device instance, void token, void *data)
	{
	const struct icmsg_config_t *conf = instance->config;
	struct backend_data_t *dev_data = instance->data;
	void *icmsg_buffer = user_buffer_to_icmsg_buffer(data);

	return icmsg_hold_rx_buffer(conf, &dev_data->icmsg_data, icmsg_buffer);
	}

	int release_rx_buffer(const struct device instance, void token, void *data)
	{
	const struct icmsg_config_t *conf = instance->config;
	struct backend_data_t *dev_data = instance->data;
	void *icmsg_buffer = user_buffer_to_icmsg_buffer(data);

	return icmsg_release_rx_buffer(conf, &dev_data->icmsg_data,
	icmsg_buffer);
	}
	#endif /* CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_NOCOPY_RX */

	const static struct ipc_service_backend backend_ops = {
	.open_instance = open,
	.register_endpoint = register_ept,
	.send = send,

	.get_tx_buffer = get_tx_buffer,
	.drop_tx_buffer = drop_tx_buffer,
	.send_nocopy = send_nocopy,

	#ifdef CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_NOCOPY_RX
	.hold_rx_buffer = hold_rx_buffer,
	.release_rx_buffer = release_rx_buffer,
	#endif
	};

	static int backend_init(const struct device *instance)
	{
	const struct icmsg_config_t *conf = instance->config;
	struct backend_data_t *dev_data = instance->data;

	k_event_init(&dev_data->event);
	k_mutex_init(&dev_data->epts_mutex);
	k_mutex_init(&dev_data->send_mutex);

	return icmsg_init(conf, &dev_data->icmsg_data);
	}

	#define BACKEND_CONFIG_POPULATE(i) \
	{ \
	.tx_shm_size = DT_REG_SIZE(DT_INST_PHANDLE(i, tx_region)), \
	.tx_shm_addr = DT_REG_ADDR(DT_INST_PHANDLE(i, tx_region)), \
	.rx_shm_size = DT_REG_SIZE(DT_INST_PHANDLE(i, rx_region)), \
	.rx_shm_addr = DT_REG_ADDR(DT_INST_PHANDLE(i, rx_region)), \
	.mbox_tx = MBOX_DT_CHANNEL_GET(DT_DRV_INST(i), tx), \
	.mbox_rx = MBOX_DT_CHANNEL_GET(DT_DRV_INST(i), rx), \
	}

	#define DEFINE_BACKEND_DEVICE(i) \
	static const struct icmsg_config_t backend_config_##i = \
	BACKEND_CONFIG_POPULATE(i); \
	static struct backend_data_t backend_data_##i; \
	\
	DEVICE_DT_INST_DEFINE(i, \
	&backend_init, \
	NULL, \
	&backend_data_##i, \
	&backend_config_##i, \
	POST_KERNEL, \
	CONFIG_IPC_SERVICE_REG_BACKEND_PRIORITY, \
	&backend_ops);

	DT_INST_FOREACH_STATUS_OKAY(DEFINE_BACKEND_DEVICE)

	#if defined(CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_SHMEM_RESET)
	#define BACKEND_CONFIG_DEFINE(i) BACKEND_CONFIG_POPULATE(i),
	static int shared_memory_prepare(const struct device *arg)
	{
	const struct icmsg_config_t *backend_config;
	const struct icmsg_config_t backend_configs[] = {
	DT_INST_FOREACH_STATUS_OKAY(BACKEND_CONFIG_DEFINE)
	};

	for (backend_config = backend_configs;
	backend_config < backend_configs + ARRAY_SIZE(backend_configs);
	backend_config++) {
	icmsg_clear_tx_memory(backend_config);
	icmsg_clear_rx_memory(backend_config);
	}

	return 0;
	}

	SYS_INIT(shared_memory_prepare, PRE_KERNEL_1, 1);
	#endif /* CONFIG_IPC_SERVICE_BACKEND_ICMSG_ME_SHMEM_RESET */