// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) ST-Ericsson AB 2010
 * Author:      Sjur Brendeland
 */

#include <linux/hardirq.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/types.h>
#include <linux/skbuff.h>
#include <linux/netdevice.h>
#include <linux/rtnetlink.h>
#include <linux/tty.h>
#include <linux/file.h>
#include <linux/if_arp.h>
#include <net/caif/caif_device.h>
#include <net/caif/cfcnfg.h>
#include <linux/err.h>
#include <linux/debugfs.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Sjur Brendeland");
MODULE_DESCRIPTION("CAIF serial device TTY line discipline");
MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_CAIF);

#define SEND_QUEUE_LOW 10
#define SEND_QUEUE_HIGH 100
#define CAIF_SENDING            1 /* Bit 1 = 0x02*/
#define CAIF_FLOW_OFF_SENT      4 /* Bit 4 = 0x10 */
#define MAX_WRITE_CHUNK      4096
#define ON 1
#define OFF 0
#define CAIF_MAX_MTU 4096

static DEFINE_SPINLOCK(ser_lock);
static LIST_HEAD(ser_list);
static LIST_HEAD(ser_release_list);

static bool ser_loop;
module_param(ser_loop, bool, 0444);
MODULE_PARM_DESC(ser_loop, "Run in simulated loopback mode.");

static bool ser_use_stx = true;
module_param(ser_use_stx, bool, 0444);
MODULE_PARM_DESC(ser_use_stx, "STX enabled or not.");

static bool ser_use_fcs = true;

module_param(ser_use_fcs, bool, 0444);
MODULE_PARM_DESC(ser_use_fcs, "FCS enabled or not.");

static int ser_write_chunk = MAX_WRITE_CHUNK;
module_param(ser_write_chunk, int, 0444);

MODULE_PARM_DESC(ser_write_chunk, "Maximum size of data written to UART.");

static struct dentry *debugfsdir;

static int caif_net_open(struct net_device *dev);
static int caif_net_close(struct net_device *dev);

struct ser_device {
        struct caif_dev_common common;
        struct list_head node;
        struct net_device *dev;
        struct sk_buff_head head;
        struct tty_struct *tty;
        bool tx_started;
        unsigned long state;
#ifdef CONFIG_DEBUG_FS
        struct dentry *debugfs_tty_dir;
        struct debugfs_blob_wrapper tx_blob;
        struct debugfs_blob_wrapper rx_blob;
        u8 rx_data[128];
        u8 tx_data[128];
        u8 tty_status;

#endif
};

static void caifdev_setup(struct net_device *dev);
static void ldisc_tx_wakeup(struct tty_struct *tty);
#ifdef CONFIG_DEBUG_FS
static inline void update_tty_status(struct ser_device *ser)
{
        ser->tty_status =
                ser->tty->flow.stopped << 5 |
                ser->tty->flow.tco_stopped << 3 |
                ser->tty->ctrl.packet << 2;
}
static inline void debugfs_init(struct ser_device *ser, struct tty_struct *tty)
{
        ser->debugfs_tty_dir = debugfs_create_dir(tty->name, debugfsdir);

        debugfs_create_blob("last_tx_msg", 0400, ser->debugfs_tty_dir,
                            &ser->tx_blob);

        debugfs_create_blob("last_rx_msg", 0400, ser->debugfs_tty_dir,
                            &ser->rx_blob);

        debugfs_create_xul("ser_state", 0400, ser->debugfs_tty_dir,
                           &ser->state);

        debugfs_create_x8("tty_status", 0400, ser->debugfs_tty_dir,
                          &ser->tty_status);

        ser->tx_blob.data = ser->tx_data;
        ser->tx_blob.size = 0;
        ser->rx_blob.data = ser->rx_data;
        ser->rx_blob.size = 0;
}

static inline void debugfs_deinit(struct ser_device *ser)
{
        debugfs_remove_recursive(ser->debugfs_tty_dir);
}

static inline void debugfs_rx(struct ser_device *ser, const u8 *data, int size)
{
        if (size > sizeof(ser->rx_data))
                size = sizeof(ser->rx_data);
        memcpy(ser->rx_data, data, size);
        ser->rx_blob.data = ser->rx_data;
        ser->rx_blob.size = size;
}
#else
static inline void debugfs_init(struct ser_device *ser, struct tty_struct *tty)
{
}

static inline void debugfs_deinit(struct ser_device *ser)
{
}

static inline void update_tty_status(struct ser_device *ser)
{
}

static inline void debugfs_rx(struct ser_device *ser, const u8 *data, int size)
{
}
#endif

static void ldisc_receive(struct tty_struct *tty, const u8 *data,
                          const u8 *flags, size_t count)
{
        struct sk_buff *skb = NULL;
        struct ser_device *ser;
        int ret;

        ser = tty->disc_data;

        /*
         * NOTE: flags may contain information about break or overrun.
         * This is not yet handled.
         */


        /*
         * Workaround for garbage at start of transmission,
         * only enable if STX handling is not enabled.
         */
        if (!ser->common.use_stx && !ser->tx_started) {
                dev_info(&ser->dev->dev,
                        "Bytes received before initial transmission -"
                        "bytes discarded.\n");
                return;
        }

        BUG_ON(ser->dev == NULL);

        /* Get a suitable caif packet and copy in data. */
        skb = netdev_alloc_skb(ser->dev, count+1);
        if (skb == NULL)
                return;
        skb_put_data(skb, data, count);

        skb->protocol = htons(ETH_P_CAIF);
        skb_reset_mac_header(skb);
        debugfs_rx(ser, data, count);
        /* Push received packet up the stack. */
        ret = netif_rx(skb);
        if (!ret) {
                ser->dev->stats.rx_packets++;
                ser->dev->stats.rx_bytes += count;
        } else
                ++ser->dev->stats.rx_dropped;
        update_tty_status(ser);
}

static int handle_tx(struct ser_device *ser)
{
        struct tty_struct *tty;
        struct sk_buff *skb;
        int tty_wr, len, room;

        tty = ser->tty;
        ser->tx_started = true;

        /* Enter critical section */
        if (test_and_set_bit(CAIF_SENDING, &ser->state))
                return 0;

        /* skb_peek is safe because handle_tx is called after skb_queue_tail */
        while ((skb = skb_peek(&ser->head)) != NULL) {

                /* Make sure you don't write too much */
                len = skb->len;
                room = tty_write_room(tty);
                if (!room)
                        break;
                if (room > ser_write_chunk)
                        room = ser_write_chunk;
                if (len > room)
                        len = room;

                /* Write to tty or loopback */
                if (!ser_loop) {
                        tty_wr = tty->ops->write(tty, skb->data, len);
                        update_tty_status(ser);
                } else {
                        tty_wr = len;
                        ldisc_receive(tty, skb->data, NULL, len);
                }
                ser->dev->stats.tx_packets++;
                ser->dev->stats.tx_bytes += tty_wr;

                /* Error on TTY ?! */
                if (tty_wr < 0)
                        goto error;
                /* Reduce buffer written, and discard if empty */
                skb_pull(skb, tty_wr);
                if (skb->len == 0) {
                        struct sk_buff *tmp = skb_dequeue(&ser->head);
                        WARN_ON(tmp != skb);
                        dev_consume_skb_any(skb);
                }
        }
        /* Send flow off if queue is empty */
        if (ser->head.qlen <= SEND_QUEUE_LOW &&
                test_and_clear_bit(CAIF_FLOW_OFF_SENT, &ser->state) &&
                ser->common.flowctrl != NULL)
                                ser->common.flowctrl(ser->dev, ON);
        clear_bit(CAIF_SENDING, &ser->state);
        return 0;
error:
        clear_bit(CAIF_SENDING, &ser->state);
        return tty_wr;
}

static netdev_tx_t caif_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct ser_device *ser;

        ser = netdev_priv(dev);

        /* Send flow off once, on high water mark */
        if (ser->head.qlen > SEND_QUEUE_HIGH &&
                !test_and_set_bit(CAIF_FLOW_OFF_SENT, &ser->state) &&
                ser->common.flowctrl != NULL)

                ser->common.flowctrl(ser->dev, OFF);

        skb_queue_tail(&ser->head, skb);
        return handle_tx(ser);
}


static void ldisc_tx_wakeup(struct tty_struct *tty)
{
        struct ser_device *ser;

        ser = tty->disc_data;
        BUG_ON(ser == NULL);
        WARN_ON(ser->tty != tty);
        handle_tx(ser);
}


static void ser_release(struct work_struct *work)
{
        struct list_head list;
        struct ser_device *ser, *tmp;
        struct tty_struct *tty;

        spin_lock(&ser_lock);
        list_replace_init(&ser_release_list, &list);
        spin_unlock(&ser_lock);

        if (!list_empty(&list)) {
                rtnl_lock();
                list_for_each_entry_safe(ser, tmp, &list, node) {
                        tty = ser->tty;
                        dev_close(ser->dev);
                        unregister_netdevice(ser->dev);
                        debugfs_deinit(ser);
                        tty_kref_put(tty->link);
                        tty_kref_put(tty);
                }
                rtnl_unlock();
        }
}

static DECLARE_WORK(ser_release_work, ser_release);

static int ldisc_open(struct tty_struct *tty)
{
        struct ser_device *ser;
        struct net_device *dev;
        char name[64];
        int result;

        /* No write no play */
        if (tty->ops->write == NULL)
                return -EOPNOTSUPP;
        if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_TTY_CONFIG))
                return -EPERM;

        /* release devices to avoid name collision */
        ser_release(NULL);

        result = snprintf(name, sizeof(name), "cf%s", tty->name);
        if (result >= IFNAMSIZ)
                return -EINVAL;
        dev = alloc_netdev(sizeof(*ser), name, NET_NAME_UNKNOWN,
                           caifdev_setup);
        if (!dev)
                return -ENOMEM;

        ser = netdev_priv(dev);
        ser->tty = tty_kref_get(tty);
        tty_kref_get(tty->link);
        ser->dev = dev;
        debugfs_init(ser, tty);
        tty->receive_room = 4096;
        tty->disc_data = ser;
        set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
        rtnl_lock();
        result = register_netdevice(dev);
        if (result) {
                tty_kref_put(tty->link);
                tty_kref_put(tty);
                rtnl_unlock();
                free_netdev(dev);
                return -ENODEV;
        }

        spin_lock(&ser_lock);
        list_add(&ser->node, &ser_list);
        spin_unlock(&ser_lock);
        rtnl_unlock();
        netif_stop_queue(dev);
        update_tty_status(ser);
        return 0;
}

static void ldisc_close(struct tty_struct *tty)
{
        struct ser_device *ser = tty->disc_data;

        spin_lock(&ser_lock);
        list_move(&ser->node, &ser_release_list);
        spin_unlock(&ser_lock);
        schedule_work(&ser_release_work);
}

/* The line discipline structure. */
static struct tty_ldisc_ops caif_ldisc = {
        .owner =        THIS_MODULE,
        .num =          N_CAIF,
        .name =         "n_caif",
        .open =         ldisc_open,
        .close =        ldisc_close,
        .receive_buf =  ldisc_receive,
        .write_wakeup = ldisc_tx_wakeup
};

static const struct net_device_ops netdev_ops = {
        .ndo_open = caif_net_open,
        .ndo_stop = caif_net_close,
        .ndo_start_xmit = caif_xmit
};

static void caifdev_setup(struct net_device *dev)
{
        struct ser_device *serdev = netdev_priv(dev);

        dev->features = 0;
        dev->netdev_ops = &netdev_ops;
        dev->type = ARPHRD_CAIF;
        dev->flags = IFF_POINTOPOINT | IFF_NOARP;
        dev->mtu = CAIF_MAX_MTU;
        dev->priv_flags |= IFF_NO_QUEUE;
        dev->needs_free_netdev = true;
        skb_queue_head_init(&serdev->head);
        serdev->common.link_select = CAIF_LINK_LOW_LATENCY;
        serdev->common.use_frag = true;
        serdev->common.use_stx = ser_use_stx;
        serdev->common.use_fcs = ser_use_fcs;
        serdev->dev = dev;
}


static int caif_net_open(struct net_device *dev)
{
        netif_wake_queue(dev);
        return 0;
}

static int caif_net_close(struct net_device *dev)
{
        netif_stop_queue(dev);
        return 0;
}

static int __init caif_ser_init(void)
{
        int ret;

        ret = tty_register_ldisc(&caif_ldisc);
        if (ret < 0)
                pr_err("cannot register CAIF ldisc=%d err=%d\n", N_CAIF, ret);

        debugfsdir = debugfs_create_dir("caif_serial", NULL);
        return ret;
}

static void __exit caif_ser_exit(void)
{
        spin_lock(&ser_lock);
        list_splice(&ser_list, &ser_release_list);
        spin_unlock(&ser_lock);
        ser_release(NULL);
        cancel_work_sync(&ser_release_work);
        tty_unregister_ldisc(&caif_ldisc);
        debugfs_remove_recursive(debugfsdir);
}

module_init(caif_ser_init);
module_exit(caif_ser_exit);