subsys/modem/modem_ppp.c

/*
 * Copyright (c) 2022 Trackunit Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr/net/ppp.h>
#include <zephyr/sys/crc.h>
#include <zephyr/modem/ppp.h>
#include <string.h>

#include <zephyr/logging/log.h>
LOG_MODULE_REGISTER(modem_ppp, CONFIG_MODEM_MODULES_LOG_LEVEL);

#define MODEM_PPP_STATE_ATTACHED_BIT	(0)
#define MODEM_PPP_FRAME_TAIL_SIZE	(2)

#define MODEM_PPP_CODE_DELIMITER	(0x7E)
#define MODEM_PPP_CODE_ESCAPE		(0x7D)
#define MODEM_PPP_VALUE_ESCAPE		(0x20)

static uint16_t modem_ppp_fcs_init(uint8_t byte)
{
	return crc16_ccitt(0xFFFF, &byte, 1);
}

static uint16_t modem_ppp_fcs_update(uint16_t fcs, uint8_t byte)
{
	return crc16_ccitt(fcs, &byte, 1);
}

static uint16_t modem_ppp_fcs_final(uint16_t fcs)
{
	return fcs ^ 0xFFFF;
}

static uint16_t modem_ppp_ppp_protocol(struct net_pkt *pkt)
{
	if (net_pkt_family(pkt) == AF_INET) {
		return PPP_IP;
	}

	if (net_pkt_family(pkt) == AF_INET6) {
		return PPP_IPV6;
	}

	LOG_WRN("Unsupported protocol");
	return 0;
}

static uint8_t modem_ppp_wrap_net_pkt_byte(struct modem_ppp *ppp)
{
	uint8_t byte;

	switch (ppp->transmit_state) {
	case MODEM_PPP_TRANSMIT_STATE_IDLE:
		LOG_WRN("Invalid transmit state");
		return 0;

	/* Writing header */
	case MODEM_PPP_TRANSMIT_STATE_SOF:
		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_HDR_FF;
		return MODEM_PPP_CODE_DELIMITER;

	case MODEM_PPP_TRANSMIT_STATE_HDR_FF:
		net_pkt_cursor_init(ppp->tx_pkt);
		ppp->tx_pkt_fcs = modem_ppp_fcs_init(0xFF);
		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_HDR_7D;
		return 0xFF;

	case MODEM_PPP_TRANSMIT_STATE_HDR_7D:
		ppp->tx_pkt_fcs = modem_ppp_fcs_update(ppp->tx_pkt_fcs, 0x03);
		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_HDR_23;
		return MODEM_PPP_CODE_ESCAPE;

	case MODEM_PPP_TRANSMIT_STATE_HDR_23:
		if (net_pkt_is_ppp(ppp->tx_pkt) == true) {
			ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_DATA;
		} else {
			ppp->tx_pkt_protocol = modem_ppp_ppp_protocol(ppp->tx_pkt);
			ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_PROTOCOL_HIGH;
		}

		return 0x23;

	/* Writing protocol */
	case MODEM_PPP_TRANSMIT_STATE_PROTOCOL_HIGH:
		byte = (ppp->tx_pkt_protocol >> 8) & 0xFF;
		ppp->tx_pkt_fcs = modem_ppp_fcs_update(ppp->tx_pkt_fcs, byte);

		if ((byte == MODEM_PPP_CODE_DELIMITER) || (byte == MODEM_PPP_CODE_ESCAPE) ||
		    (byte < MODEM_PPP_VALUE_ESCAPE)) {
			ppp->tx_pkt_escaped = byte ^ MODEM_PPP_VALUE_ESCAPE;
			ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_ESCAPING_PROTOCOL_HIGH;
			return MODEM_PPP_CODE_ESCAPE;
		}

		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_PROTOCOL_LOW;
		return byte;

	case MODEM_PPP_TRANSMIT_STATE_ESCAPING_PROTOCOL_HIGH:
		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_PROTOCOL_LOW;
		return ppp->tx_pkt_escaped;

	case MODEM_PPP_TRANSMIT_STATE_PROTOCOL_LOW:
		byte = ppp->tx_pkt_protocol & 0xFF;
		ppp->tx_pkt_fcs = modem_ppp_fcs_update(ppp->tx_pkt_fcs, byte);

		if ((byte == MODEM_PPP_CODE_DELIMITER) || (byte == MODEM_PPP_CODE_ESCAPE) ||
		    (byte < MODEM_PPP_VALUE_ESCAPE)) {
			ppp->tx_pkt_escaped = byte ^ MODEM_PPP_VALUE_ESCAPE;
			ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_ESCAPING_PROTOCOL_LOW;
			return MODEM_PPP_CODE_ESCAPE;
		}

		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_DATA;
		return byte;

	case MODEM_PPP_TRANSMIT_STATE_ESCAPING_PROTOCOL_LOW:
		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_DATA;
		return ppp->tx_pkt_escaped;

	/* Writing data */
	case MODEM_PPP_TRANSMIT_STATE_DATA:
		(void)net_pkt_read_u8(ppp->tx_pkt, &byte);
		ppp->tx_pkt_fcs = modem_ppp_fcs_update(ppp->tx_pkt_fcs, byte);

		if ((byte == MODEM_PPP_CODE_DELIMITER) || (byte == MODEM_PPP_CODE_ESCAPE) ||
		    (byte < MODEM_PPP_VALUE_ESCAPE)) {
			ppp->tx_pkt_escaped = byte ^ MODEM_PPP_VALUE_ESCAPE;
			ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_ESCAPING_DATA;
			return MODEM_PPP_CODE_ESCAPE;
		}

		if (net_pkt_remaining_data(ppp->tx_pkt) == 0) {
			ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_FCS_LOW;
		}

		return byte;

	case MODEM_PPP_TRANSMIT_STATE_ESCAPING_DATA:
		if (net_pkt_remaining_data(ppp->tx_pkt) == 0) {
			ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_FCS_LOW;
		} else {
			ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_DATA;
		}

		return ppp->tx_pkt_escaped;

	/* Writing FCS */
	case MODEM_PPP_TRANSMIT_STATE_FCS_LOW:
		ppp->tx_pkt_fcs = modem_ppp_fcs_final(ppp->tx_pkt_fcs);
		byte = ppp->tx_pkt_fcs & 0xFF;

		if ((byte == MODEM_PPP_CODE_DELIMITER) || (byte == MODEM_PPP_CODE_ESCAPE) ||
		    (byte < MODEM_PPP_VALUE_ESCAPE)) {
			ppp->tx_pkt_escaped = byte ^ MODEM_PPP_VALUE_ESCAPE;
			ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_ESCAPING_FCS_LOW;
			return MODEM_PPP_CODE_ESCAPE;
		}

		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_FCS_HIGH;
		return byte;

	case MODEM_PPP_TRANSMIT_STATE_ESCAPING_FCS_LOW:
		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_FCS_HIGH;
		return ppp->tx_pkt_escaped;

	case MODEM_PPP_TRANSMIT_STATE_FCS_HIGH:
		byte = (ppp->tx_pkt_fcs >> 8) & 0xFF;

		if ((byte == MODEM_PPP_CODE_DELIMITER) || (byte == MODEM_PPP_CODE_ESCAPE) ||
		    (byte < MODEM_PPP_VALUE_ESCAPE)) {
			ppp->tx_pkt_escaped = byte ^ MODEM_PPP_VALUE_ESCAPE;
			ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_ESCAPING_FCS_HIGH;
			return MODEM_PPP_CODE_ESCAPE;
		}

		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_EOF;
		return byte;

	case MODEM_PPP_TRANSMIT_STATE_ESCAPING_FCS_HIGH:
		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_EOF;
		return ppp->tx_pkt_escaped;

	/* Writing end of frame */
	case MODEM_PPP_TRANSMIT_STATE_EOF:
		ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_IDLE;
		return MODEM_PPP_CODE_DELIMITER;
	}

	return 0;
}

static bool modem_ppp_is_byte_expected(uint8_t byte, uint8_t expected_byte)
{
	if (byte == expected_byte) {
		return true;
	}
	LOG_DBG("Dropping byte 0x%02hhx because 0x%02hhx was expected.", byte, expected_byte);
	return false;
}

static void modem_ppp_process_received_byte(struct modem_ppp *ppp, uint8_t byte)
{
	switch (ppp->receive_state) {
	case MODEM_PPP_RECEIVE_STATE_HDR_SOF:
		if (modem_ppp_is_byte_expected(byte, MODEM_PPP_CODE_DELIMITER)) {
			ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_FF;
		}
		break;

	case MODEM_PPP_RECEIVE_STATE_HDR_FF:
		if (byte == MODEM_PPP_CODE_DELIMITER) {
			break;
		}
		if (modem_ppp_is_byte_expected(byte, 0xFF)) {
			ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_7D;
		} else {
			ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_SOF;
		}
		break;

	case MODEM_PPP_RECEIVE_STATE_HDR_7D:
		if (modem_ppp_is_byte_expected(byte, MODEM_PPP_CODE_ESCAPE)) {
			ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_23;
		} else {
			ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_SOF;
		}
		break;

	case MODEM_PPP_RECEIVE_STATE_HDR_23:
		if (modem_ppp_is_byte_expected(byte, 0x23)) {
			ppp->rx_pkt = net_pkt_rx_alloc_with_buffer(ppp->iface,
				CONFIG_MODEM_PPP_NET_BUF_FRAG_SIZE, AF_UNSPEC, 0, K_NO_WAIT);

			if (ppp->rx_pkt == NULL) {
				LOG_WRN("Dropped frame, no net_pkt available");
				ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_SOF;
				break;
			}

			LOG_DBG("Receiving PPP frame");
			ppp->receive_state = MODEM_PPP_RECEIVE_STATE_WRITING;
			net_pkt_cursor_init(ppp->rx_pkt);
		} else {
			ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_SOF;
		}

		break;

	case MODEM_PPP_RECEIVE_STATE_WRITING:
		if (byte == MODEM_PPP_CODE_DELIMITER) {
			LOG_DBG("Received PPP frame (len %zu)", net_pkt_get_len(ppp->rx_pkt));

			/* Remove FCS */
			net_pkt_remove_tail(ppp->rx_pkt, MODEM_PPP_FRAME_TAIL_SIZE);
			net_pkt_set_ppp(ppp->rx_pkt, true);

			if (net_recv_data(ppp->iface, ppp->rx_pkt) < 0) {
				LOG_WRN("Net pkt could not be processed");
				net_pkt_unref(ppp->rx_pkt);
			}

			ppp->rx_pkt = NULL;
			/* Skip SOF because the delimiter may be omitted for successive frames. */
			ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_FF;
			break;
		}

		if (net_pkt_available_buffer(ppp->rx_pkt) == 1) {
			if (net_pkt_alloc_buffer(ppp->rx_pkt, CONFIG_MODEM_PPP_NET_BUF_FRAG_SIZE,
						 AF_INET, K_NO_WAIT) < 0) {
				LOG_WRN("Failed to alloc buffer");
				net_pkt_unref(ppp->rx_pkt);
				ppp->rx_pkt = NULL;
				ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_SOF;
				break;
			}
		}

		if (byte == MODEM_PPP_CODE_ESCAPE) {
			ppp->receive_state = MODEM_PPP_RECEIVE_STATE_UNESCAPING;
			break;
		}

		if (net_pkt_write_u8(ppp->rx_pkt, byte) < 0) {
			LOG_WRN("Dropped PPP frame");
			net_pkt_unref(ppp->rx_pkt);
			ppp->rx_pkt = NULL;
			ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_SOF;
#if defined(CONFIG_NET_STATISTICS_PPP)
			ppp->stats.drop++;
#endif
		}

		break;

	case MODEM_PPP_RECEIVE_STATE_UNESCAPING:
		if (net_pkt_write_u8(ppp->rx_pkt, (byte ^ MODEM_PPP_VALUE_ESCAPE)) < 0) {
			LOG_WRN("Dropped PPP frame");
			net_pkt_unref(ppp->rx_pkt);
			ppp->rx_pkt = NULL;
			ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_SOF;
#if defined(CONFIG_NET_STATISTICS_PPP)
			ppp->stats.drop++;
#endif
			break;
		}

		ppp->receive_state = MODEM_PPP_RECEIVE_STATE_WRITING;
		break;
	}
}

#if CONFIG_MODEM_STATS
static uint32_t get_transmit_buf_length(struct modem_ppp *ppp)
{
	return ring_buf_size_get(&ppp->transmit_rb);
}

static void advertise_transmit_buf_stats(struct modem_ppp *ppp)
{
	uint32_t length;

	length = get_transmit_buf_length(ppp);
	modem_stats_buffer_advertise_length(&ppp->transmit_buf_stats, length);
}

static void advertise_receive_buf_stats(struct modem_ppp *ppp, uint32_t length)
{
	modem_stats_buffer_advertise_length(&ppp->receive_buf_stats, length);
}
#endif

static void modem_ppp_pipe_callback(struct modem_pipe *pipe, enum modem_pipe_event event,
				    void *user_data)
{
	struct modem_ppp *ppp = (struct modem_ppp *)user_data;

	switch (event) {
	case MODEM_PIPE_EVENT_RECEIVE_READY:
		k_work_submit(&ppp->process_work);
		break;

	case MODEM_PIPE_EVENT_OPENED:
	case MODEM_PIPE_EVENT_TRANSMIT_IDLE:
		k_work_submit(&ppp->send_work);
		break;

	default:
		break;
	}
}

static void modem_ppp_send_handler(struct k_work *item)
{
	struct modem_ppp *ppp = CONTAINER_OF(item, struct modem_ppp, send_work);
	uint8_t byte;
	uint8_t *reserved;
	uint32_t reserved_size;
	int ret;

	if (ppp->tx_pkt == NULL) {
		ppp->tx_pkt = k_fifo_get(&ppp->tx_pkt_fifo, K_NO_WAIT);
	}

	if (ppp->tx_pkt != NULL) {
		/* Initialize wrap */
		if (ppp->transmit_state == MODEM_PPP_TRANSMIT_STATE_IDLE) {
			ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_SOF;
		}

		/* Fill transmit ring buffer */
		while (ring_buf_space_get(&ppp->transmit_rb) > 0) {
			byte = modem_ppp_wrap_net_pkt_byte(ppp);

			ring_buf_put(&ppp->transmit_rb, &byte, 1);

			if (ppp->transmit_state == MODEM_PPP_TRANSMIT_STATE_IDLE) {
				net_pkt_unref(ppp->tx_pkt);
				ppp->tx_pkt = k_fifo_get(&ppp->tx_pkt_fifo, K_NO_WAIT);
				break;
			}
		}
	}

#if CONFIG_MODEM_STATS
	advertise_transmit_buf_stats(ppp);
#endif

	while (!ring_buf_is_empty(&ppp->transmit_rb)) {
		reserved_size = ring_buf_get_claim(&ppp->transmit_rb, &reserved, UINT32_MAX);

		ret = modem_pipe_transmit(ppp->pipe, reserved, reserved_size);
		if (ret < 0) {
			ring_buf_get_finish(&ppp->transmit_rb, 0);
			break;
		}

		ring_buf_get_finish(&ppp->transmit_rb, (uint32_t)ret);

		if (ret < reserved_size) {
			break;
		}
	}
}

static void modem_ppp_process_handler(struct k_work *item)
{
	struct modem_ppp *ppp = CONTAINER_OF(item, struct modem_ppp, process_work);
	int ret;

	ret = modem_pipe_receive(ppp->pipe, ppp->receive_buf, ppp->buf_size);
	if (ret < 1) {
		return;
	}

#if CONFIG_MODEM_STATS
	advertise_receive_buf_stats(ppp, ret);
#endif

	for (int i = 0; i < ret; i++) {
		modem_ppp_process_received_byte(ppp, ppp->receive_buf[i]);
	}

	k_work_submit(&ppp->process_work);
}

static void modem_ppp_ppp_api_init(struct net_if *iface)
{
	const struct device *dev = net_if_get_device(iface);
	struct modem_ppp *ppp = (struct modem_ppp *)dev->data;

	net_ppp_init(iface);
	net_if_flag_set(iface, NET_IF_NO_AUTO_START);
	net_if_carrier_off(iface);

	if (ppp->init_iface != NULL) {
		ppp->init_iface(iface);
	}

	ppp->iface = iface;
}

static int modem_ppp_ppp_api_start(const struct device *dev)
{
	return 0;
}

static int modem_ppp_ppp_api_stop(const struct device *dev)
{
	return 0;
}

static int modem_ppp_ppp_api_send(const struct device *dev, struct net_pkt *pkt)
{
	struct modem_ppp *ppp = (struct modem_ppp *)dev->data;

	if (atomic_test_bit(&ppp->state, MODEM_PPP_STATE_ATTACHED_BIT) == false) {
		return -EPERM;
	}

	/* Validate packet protocol */
	if ((net_pkt_is_ppp(pkt) == false) && (net_pkt_family(pkt) != AF_INET) &&
	    (net_pkt_family(pkt) != AF_INET6)) {
		return -EPROTONOSUPPORT;
	}

	/* Validate packet data length */
	if (((net_pkt_get_len(pkt) < 2) && (net_pkt_is_ppp(pkt) == true)) ||
	    ((net_pkt_get_len(pkt) < 1))) {
		return -ENODATA;
	}

	net_pkt_ref(pkt);
	k_fifo_put(&ppp->tx_pkt_fifo, pkt);
	k_work_submit(&ppp->send_work);
	return 0;
}

#if defined(CONFIG_NET_STATISTICS_PPP)
static struct net_stats_ppp *modem_ppp_ppp_get_stats(const struct device *dev)
{
	struct modem_ppp *ppp = (struct modem_ppp *)dev->data;

	return &ppp->stats;
}
#endif

#if CONFIG_MODEM_STATS
static uint32_t get_buf_size(struct modem_ppp *ppp)
{
	return ppp->buf_size;
}

static void init_buf_stats(struct modem_ppp *ppp)
{
	char iface_name[CONFIG_MODEM_STATS_BUFFER_NAME_SIZE - sizeof("_xx")];
	char name[CONFIG_MODEM_STATS_BUFFER_NAME_SIZE];
	int ret;
	uint32_t size;

	ret = net_if_get_name(ppp->iface, iface_name, sizeof(iface_name));
	if (ret < 0) {
		snprintk(iface_name, sizeof(iface_name), "ppp");
	}

	size = get_buf_size(ppp);
	snprintk(name, sizeof(name), "%s_rx", iface_name);
	modem_stats_buffer_init(&ppp->receive_buf_stats, name, size);
	snprintk(name, sizeof(name), "%s_tx", iface_name);
	modem_stats_buffer_init(&ppp->transmit_buf_stats, name, size);
}
#endif

const struct ppp_api modem_ppp_ppp_api = {
	.iface_api.init = modem_ppp_ppp_api_init,
	.start = modem_ppp_ppp_api_start,
	.stop = modem_ppp_ppp_api_stop,
	.send = modem_ppp_ppp_api_send,
#if defined(CONFIG_NET_STATISTICS_PPP)
	.get_stats = modem_ppp_ppp_get_stats,
#endif
};

int modem_ppp_attach(struct modem_ppp *ppp, struct modem_pipe *pipe)
{
	if (atomic_test_bit(&ppp->state, MODEM_PPP_STATE_ATTACHED_BIT) == true) {
		return 0;
	}

	ppp->pipe = pipe;
	modem_pipe_attach(pipe, modem_ppp_pipe_callback, ppp);

	atomic_set_bit(&ppp->state, MODEM_PPP_STATE_ATTACHED_BIT);
	return 0;
}

struct net_if *modem_ppp_get_iface(struct modem_ppp *ppp)
{
	return ppp->iface;
}

void modem_ppp_release(struct modem_ppp *ppp)
{
	struct k_work_sync sync;
	struct net_pkt *pkt;

	if (atomic_test_and_clear_bit(&ppp->state, MODEM_PPP_STATE_ATTACHED_BIT) == false) {
		return;
	}

	modem_pipe_release(ppp->pipe);
	k_work_cancel_sync(&ppp->send_work, &sync);
	k_work_cancel_sync(&ppp->process_work, &sync);
	ppp->pipe = NULL;
	ppp->receive_state = MODEM_PPP_RECEIVE_STATE_HDR_SOF;

	if (ppp->rx_pkt != NULL) {
		net_pkt_unref(ppp->rx_pkt);
		ppp->rx_pkt = NULL;
	}

	ppp->transmit_state = MODEM_PPP_TRANSMIT_STATE_IDLE;

	if (ppp->tx_pkt != NULL) {
		net_pkt_unref(ppp->tx_pkt);
		ppp->tx_pkt = NULL;
	}

	while (1) {
		pkt = k_fifo_get(&ppp->tx_pkt_fifo, K_NO_WAIT);
		if (pkt == NULL) {
			break;
		}

		net_pkt_unref(pkt);
	}
}

int modem_ppp_init_internal(const struct device *dev)
{
	struct modem_ppp *ppp = (struct modem_ppp *)dev->data;

	atomic_set(&ppp->state, 0);
	ring_buf_init(&ppp->transmit_rb, ppp->buf_size, ppp->transmit_buf);
	k_work_init(&ppp->send_work, modem_ppp_send_handler);
	k_work_init(&ppp->process_work, modem_ppp_process_handler);
	k_fifo_init(&ppp->tx_pkt_fifo);

#if CONFIG_MODEM_STATS
	init_buf_stats(ppp);
#endif
	return 0;
}