// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2015, Marvell International Ltd.
 *
 * Inspired (hugely) by HCI LDISC implementation in Bluetooth.
 *
 *  Copyright (C) 2000-2001  Qualcomm Incorporated
 *  Copyright (C) 2002-2003  Maxim Krasnyansky <maxk@qualcomm.com>
 *  Copyright (C) 2004-2005  Marcel Holtmann <marcel@holtmann.org>
 */

#include <linux/module.h>

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/interrupt.h>
#include <linux/ptrace.h>
#include <linux/poll.h>

#include <linux/slab.h>
#include <linux/tty.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/signal.h>
#include <linux/ioctl.h>
#include <linux/skbuff.h>

#include <net/nfc/nci.h>
#include <net/nfc/nci_core.h>

/* TX states  */
#define NCI_UART_SENDING        1
#define NCI_UART_TX_WAKEUP      2

static struct nci_uart *nci_uart_drivers[NCI_UART_DRIVER_MAX];

static inline struct sk_buff *nci_uart_dequeue(struct nci_uart *nu)
{
        struct sk_buff *skb = nu->tx_skb;

        if (!skb)
                skb = skb_dequeue(&nu->tx_q);
        else
                nu->tx_skb = NULL;

        return skb;
}

static inline int nci_uart_queue_empty(struct nci_uart *nu)
{
        if (nu->tx_skb)
                return 0;

        return skb_queue_empty(&nu->tx_q);
}

static int nci_uart_tx_wakeup(struct nci_uart *nu)
{
        if (test_and_set_bit(NCI_UART_SENDING, &nu->tx_state)) {
                set_bit(NCI_UART_TX_WAKEUP, &nu->tx_state);
                return 0;
        }

        schedule_work(&nu->write_work);

        return 0;
}

static void nci_uart_write_work(struct work_struct *work)
{
        struct nci_uart *nu = container_of(work, struct nci_uart, write_work);
        struct tty_struct *tty = nu->tty;
        struct sk_buff *skb;

restart:
        clear_bit(NCI_UART_TX_WAKEUP, &nu->tx_state);

        if (nu->ops.tx_start)
                nu->ops.tx_start(nu);

        while ((skb = nci_uart_dequeue(nu))) {
                int len;

                set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
                len = tty->ops->write(tty, skb->data, skb->len);
                skb_pull(skb, len);
                if (skb->len) {
                        nu->tx_skb = skb;
                        break;
                }
                kfree_skb(skb);
        }

        if (test_bit(NCI_UART_TX_WAKEUP, &nu->tx_state))
                goto restart;

        if (nu->ops.tx_done && nci_uart_queue_empty(nu))
                nu->ops.tx_done(nu);

        clear_bit(NCI_UART_SENDING, &nu->tx_state);
}

static int nci_uart_set_driver(struct tty_struct *tty, unsigned int driver)
{
        struct nci_uart *nu = NULL;
        int ret;

        if (driver >= NCI_UART_DRIVER_MAX)
                return -EINVAL;

        if (!nci_uart_drivers[driver])
                return -ENOENT;

        nu = kzalloc_obj(*nu);
        if (!nu)
                return -ENOMEM;

        memcpy(nu, nci_uart_drivers[driver], sizeof(struct nci_uart));
        nu->tty = tty;
        skb_queue_head_init(&nu->tx_q);
        INIT_WORK(&nu->write_work, nci_uart_write_work);
        spin_lock_init(&nu->rx_lock);

        ret = nu->ops.open(nu);
        if (ret) {
                kfree(nu);
                return ret;
        } else if (!try_module_get(nu->owner)) {
                nu->ops.close(nu);
                kfree(nu);
                return -ENOENT;
        }
        tty->disc_data = nu;

        return 0;
}

/* ------ LDISC part ------ */

/* nci_uart_tty_open
 *
 *     Called when line discipline changed to NCI_UART.
 *
 * Arguments:
 *     tty    pointer to tty info structure
 * Return Value:
 *     0 if success, otherwise error code
 */
static int nci_uart_tty_open(struct tty_struct *tty)
{
        /* Error if the tty has no write op instead of leaving an exploitable
         * hole
         */
        if (!tty->ops->write)
                return -EOPNOTSUPP;

        tty->disc_data = NULL;
        tty->receive_room = 65536;

        /* Flush any pending characters in the driver */
        tty_driver_flush_buffer(tty);

        return 0;
}

/* nci_uart_tty_close()
 *
 *    Called when the line discipline is changed to something
 *    else, the tty is closed, or the tty detects a hangup.
 */
static void nci_uart_tty_close(struct tty_struct *tty)
{
        struct nci_uart *nu = tty->disc_data;

        /* Detach from the tty */
        tty->disc_data = NULL;

        if (!nu)
                return;

        kfree_skb(nu->tx_skb);
        kfree_skb(nu->rx_skb);

        skb_queue_purge(&nu->tx_q);

        nu->ops.close(nu);
        nu->tty = NULL;
        module_put(nu->owner);

        cancel_work_sync(&nu->write_work);

        kfree(nu);
}

/* nci_uart_tty_wakeup()
 *
 *    Callback for transmit wakeup. Called when low level
 *    device driver can accept more send data.
 *
 * Arguments:        tty    pointer to associated tty instance data
 * Return Value:    None
 */
static void nci_uart_tty_wakeup(struct tty_struct *tty)
{
        struct nci_uart *nu = tty->disc_data;

        if (!nu)
                return;

        clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);

        if (tty != nu->tty)
                return;

        nci_uart_tx_wakeup(nu);
}

/* -- Default recv_buf handler --
 *
 * This handler supposes that NCI frames are sent over UART link without any
 * framing. It reads NCI header, retrieve the packet size and once all packet
 * bytes are received it passes it to nci_uart driver for processing.
 */
static int nci_uart_default_recv_buf(struct nci_uart *nu, const u8 *data,
                                     int count)
{
        int chunk_len;

        if (!nu->ndev) {
                nfc_err(nu->tty->dev,
                        "receive data from tty but no NCI dev is attached yet, drop buffer\n");
                return 0;
        }

        /* Decode all incoming data in packets
         * and enqueue then for processing.
         */
        while (count > 0) {
                /* If this is the first data of a packet, allocate a buffer */
                if (!nu->rx_skb) {
                        nu->rx_packet_len = -1;
                        nu->rx_skb = nci_skb_alloc(nu->ndev,
                                                   NCI_MAX_PACKET_SIZE,
                                                   GFP_ATOMIC);
                        if (!nu->rx_skb)
                                return -ENOMEM;
                }

                /* Eat byte after byte till full packet header is received */
                if (nu->rx_skb->len < NCI_CTRL_HDR_SIZE) {
                        skb_put_u8(nu->rx_skb, *data++);
                        --count;
                        continue;
                }

                /* Header was received but packet len was not read */
                if (nu->rx_packet_len < 0)
                        nu->rx_packet_len = NCI_CTRL_HDR_SIZE +
                                nci_plen(nu->rx_skb->data);

                /* Compute how many bytes are missing and how many bytes can
                 * be consumed.
                 */
                chunk_len = nu->rx_packet_len - nu->rx_skb->len;
                if (count < chunk_len)
                        chunk_len = count;
                skb_put_data(nu->rx_skb, data, chunk_len);
                data += chunk_len;
                count -= chunk_len;

                /* Check if packet is fully received */
                if (nu->rx_packet_len == nu->rx_skb->len) {
                        /* Pass RX packet to driver */
                        if (nu->ops.recv(nu, nu->rx_skb) != 0)
                                nfc_err(nu->tty->dev, "corrupted RX packet\n");
                        /* Next packet will be a new one */
                        nu->rx_skb = NULL;
                }
        }

        return 0;
}

/* nci_uart_tty_receive()
 *
 *     Called by tty low level driver when receive data is
 *     available.
 *
 * Arguments:  tty          pointer to tty instance data
 *             data         pointer to received data
 *             flags        pointer to flags for data
 *             count        count of received data in bytes
 *
 * Return Value:    None
 */
static void nci_uart_tty_receive(struct tty_struct *tty, const u8 *data,
                                 const u8 *flags, size_t count)
{
        struct nci_uart *nu = tty->disc_data;

        if (!nu || tty != nu->tty)
                return;

        spin_lock(&nu->rx_lock);
        nci_uart_default_recv_buf(nu, data, count);
        spin_unlock(&nu->rx_lock);

        tty_unthrottle(tty);
}

/* nci_uart_tty_ioctl()
 *
 *    Process IOCTL system call for the tty device.
 *
 * Arguments:
 *
 *    tty        pointer to tty instance data
 *    cmd        IOCTL command code
 *    arg        argument for IOCTL call (cmd dependent)
 *
 * Return Value:    Command dependent
 */
static int nci_uart_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
                              unsigned long arg)
{
        struct nci_uart *nu = tty->disc_data;
        int err = 0;

        switch (cmd) {
        case NCIUARTSETDRIVER:
                if (!nu)
                        return nci_uart_set_driver(tty, (unsigned int)arg);
                else
                        return -EBUSY;
                break;
        default:
                err = n_tty_ioctl_helper(tty, cmd, arg);
                break;
        }

        return err;
}

/* We don't provide read/write/poll interface for user space. */
static ssize_t nci_uart_tty_read(struct tty_struct *tty, struct file *file,
                                 u8 *buf, size_t nr, void **cookie,
                                 unsigned long offset)
{
        return 0;
}

static ssize_t nci_uart_tty_write(struct tty_struct *tty, struct file *file,
                                  const u8 *data, size_t count)
{
        return 0;
}

static int nci_uart_send(struct nci_uart *nu, struct sk_buff *skb)
{
        /* Queue TX packet */
        skb_queue_tail(&nu->tx_q, skb);

        /* Try to start TX (if possible) */
        nci_uart_tx_wakeup(nu);

        return 0;
}

int nci_uart_register(struct nci_uart *nu)
{
        if (!nu || !nu->ops.open ||
            !nu->ops.recv || !nu->ops.close)
                return -EINVAL;

        /* Set the send callback */
        nu->ops.send = nci_uart_send;

        /* Add this driver in the driver list */
        if (nci_uart_drivers[nu->driver]) {
                pr_err("driver %d is already registered\n", nu->driver);
                return -EBUSY;
        }
        nci_uart_drivers[nu->driver] = nu;

        pr_info("NCI uart driver '%s [%d]' registered\n", nu->name, nu->driver);

        return 0;
}
EXPORT_SYMBOL_GPL(nci_uart_register);

void nci_uart_unregister(struct nci_uart *nu)
{
        pr_info("NCI uart driver '%s [%d]' unregistered\n", nu->name,
                nu->driver);

        /* Remove this driver from the driver list */
        nci_uart_drivers[nu->driver] = NULL;
}
EXPORT_SYMBOL_GPL(nci_uart_unregister);

void nci_uart_set_config(struct nci_uart *nu, int baudrate, int flow_ctrl)
{
        struct ktermios new_termios;

        if (!nu->tty)
                return;

        down_read(&nu->tty->termios_rwsem);
        new_termios = nu->tty->termios;
        up_read(&nu->tty->termios_rwsem);
        tty_termios_encode_baud_rate(&new_termios, baudrate, baudrate);

        if (flow_ctrl)
                new_termios.c_cflag |= CRTSCTS;
        else
                new_termios.c_cflag &= ~CRTSCTS;

        tty_set_termios(nu->tty, &new_termios);
}
EXPORT_SYMBOL_GPL(nci_uart_set_config);

static struct tty_ldisc_ops nci_uart_ldisc = {
        .owner          = THIS_MODULE,
        .num            = N_NCI,
        .name           = "n_nci",
        .open           = nci_uart_tty_open,
        .close          = nci_uart_tty_close,
        .read           = nci_uart_tty_read,
        .write          = nci_uart_tty_write,
        .receive_buf    = nci_uart_tty_receive,
        .write_wakeup   = nci_uart_tty_wakeup,
        .ioctl          = nci_uart_tty_ioctl,
        .compat_ioctl   = nci_uart_tty_ioctl,
};

static int __init nci_uart_init(void)
{
        return tty_register_ldisc(&nci_uart_ldisc);
}

static void __exit nci_uart_exit(void)
{
        tty_unregister_ldisc(&nci_uart_ldisc);
}

module_init(nci_uart_init);
module_exit(nci_uart_exit);

MODULE_AUTHOR("Marvell International Ltd.");
MODULE_DESCRIPTION("NFC NCI UART driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_NCI);