// SPDX-License-Identifier: GPL-2.0-only
/*
 * WWAN device simulator for WWAN framework testing.
 *
 * Copyright (c) 2021, Sergey Ryazanov <ryazanov.s.a@gmail.com>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/device.h>
#include <linux/spinlock.h>
#include <linux/list.h>
#include <linux/skbuff.h>
#include <linux/netdevice.h>
#include <linux/wwan.h>
#include <linux/debugfs.h>
#include <linux/workqueue.h>

#include <net/arp.h>

static int wwan_hwsim_devsnum = 2;
module_param_named(devices, wwan_hwsim_devsnum, int, 0444);
MODULE_PARM_DESC(devices, "Number of simulated devices");

static struct class *wwan_hwsim_class;

static struct dentry *wwan_hwsim_debugfs_topdir;
static struct dentry *wwan_hwsim_debugfs_devcreate;

static DEFINE_SPINLOCK(wwan_hwsim_devs_lock);
static LIST_HEAD(wwan_hwsim_devs);
static unsigned int wwan_hwsim_dev_idx;

struct wwan_hwsim_dev {
        struct list_head list;
        unsigned int id;
        struct device dev;
        struct work_struct del_work;
        struct dentry *debugfs_topdir;
        struct dentry *debugfs_portcreate;
        spinlock_t ports_lock;  /* Serialize ports creation/deletion */
        unsigned int port_idx;
        struct list_head ports;
};

struct wwan_hwsim_port {
        struct list_head list;
        unsigned int id;
        struct wwan_hwsim_dev *dev;
        struct wwan_port *wwan;
        struct work_struct del_work;
        struct dentry *debugfs_topdir;
        enum {                  /* AT command parser state */
                AT_PARSER_WAIT_A,
                AT_PARSER_WAIT_T,
                AT_PARSER_WAIT_TERM,
                AT_PARSER_SKIP_LINE,
        } pstate;
};

static const struct file_operations wwan_hwsim_debugfs_portdestroy_fops;
static const struct file_operations wwan_hwsim_debugfs_portcreate_fops;
static const struct file_operations wwan_hwsim_debugfs_devdestroy_fops;
static void wwan_hwsim_port_del_work(struct work_struct *work);
static void wwan_hwsim_dev_del_work(struct work_struct *work);

static netdev_tx_t wwan_hwsim_netdev_xmit(struct sk_buff *skb,
                                          struct net_device *ndev)
{
        ndev->stats.tx_packets++;
        ndev->stats.tx_bytes += skb->len;
        consume_skb(skb);
        return NETDEV_TX_OK;
}

static const struct net_device_ops wwan_hwsim_netdev_ops = {
        .ndo_start_xmit = wwan_hwsim_netdev_xmit,
};

static void wwan_hwsim_netdev_setup(struct net_device *ndev)
{
        ndev->netdev_ops = &wwan_hwsim_netdev_ops;
        ndev->needs_free_netdev = true;

        ndev->mtu = ETH_DATA_LEN;
        ndev->min_mtu = ETH_MIN_MTU;
        ndev->max_mtu = ETH_MAX_MTU;

        ndev->type = ARPHRD_NONE;
        ndev->flags = IFF_POINTOPOINT | IFF_NOARP;
}

static const struct wwan_ops wwan_hwsim_wwan_rtnl_ops = {
        .priv_size = 0,                 /* No private data */
        .setup = wwan_hwsim_netdev_setup,
};

static int wwan_hwsim_port_start(struct wwan_port *wport)
{
        struct wwan_hwsim_port *port = wwan_port_get_drvdata(wport);

        port->pstate = AT_PARSER_WAIT_A;

        return 0;
}

static void wwan_hwsim_port_stop(struct wwan_port *wport)
{
}

/* Implements a minimalistic AT commands parser that echo input back and
 * reply with 'OK' to each input command. See AT command protocol details in the
 * ITU-T V.250 recomendations document.
 *
 * Be aware that this processor is not fully V.250 compliant.
 */
static int wwan_hwsim_port_tx(struct wwan_port *wport, struct sk_buff *in)
{
        struct wwan_hwsim_port *port = wwan_port_get_drvdata(wport);
        struct sk_buff *out;
        int i, n, s;

        /* Estimate a max possible number of commands by counting the number of
         * termination chars (S3 param, CR by default). And then allocate the
         * output buffer that will be enough to fit the echo and result codes of
         * all commands.
         */
        for (i = 0, n = 0; i < in->len; ++i)
                if (in->data[i] == '\r')
                        n++;
        n = in->len + n * (2 + 2 + 2);  /* Output buffer size */
        out = alloc_skb(n, GFP_KERNEL);
        if (!out)
                return -ENOMEM;

        for (i = 0, s = 0; i < in->len; ++i) {
                char c = in->data[i];

                if (port->pstate == AT_PARSER_WAIT_A) {
                        if (c == 'A' || c == 'a')
                                port->pstate = AT_PARSER_WAIT_T;
                        else if (c != '\n')     /* Ignore formating char */
                                port->pstate = AT_PARSER_SKIP_LINE;
                } else if (port->pstate == AT_PARSER_WAIT_T) {
                        if (c == 'T' || c == 't')
                                port->pstate = AT_PARSER_WAIT_TERM;
                        else
                                port->pstate = AT_PARSER_SKIP_LINE;
                } else if (port->pstate == AT_PARSER_WAIT_TERM) {
                        if (c != '\r')
                                continue;
                        /* Consume the trailing formatting char as well */
                        if ((i + 1) < in->len && in->data[i + 1] == '\n')
                                i++;
                        n = i - s + 1;
                        memcpy(skb_put(out, n), &in->data[s], n);/* Echo */
                        memcpy(skb_put(out, 6), "\r\nOK\r\n", 6);
                        s = i + 1;
                        port->pstate = AT_PARSER_WAIT_A;
                } else if (port->pstate == AT_PARSER_SKIP_LINE) {
                        if (c != '\r')
                                continue;
                        port->pstate = AT_PARSER_WAIT_A;
                }
        }

        if (i > s) {
                /* Echo the processed portion of a not yet completed command */
                n = i - s;
                memcpy(skb_put(out, n), &in->data[s], n);
        }

        consume_skb(in);

        wwan_port_rx(wport, out);

        return 0;
}

static const struct wwan_port_ops wwan_hwsim_port_ops = {
        .start = wwan_hwsim_port_start,
        .stop = wwan_hwsim_port_stop,
        .tx = wwan_hwsim_port_tx,
};

static struct wwan_hwsim_port *wwan_hwsim_port_new(struct wwan_hwsim_dev *dev)
{
        struct wwan_hwsim_port *port;
        char name[0x10];
        int err;

        port = kzalloc(sizeof(*port), GFP_KERNEL);
        if (!port)
                return ERR_PTR(-ENOMEM);

        port->dev = dev;

        spin_lock(&dev->ports_lock);
        port->id = dev->port_idx++;
        spin_unlock(&dev->ports_lock);

        port->wwan = wwan_create_port(&dev->dev, WWAN_PORT_AT,
                                      &wwan_hwsim_port_ops,
                                      port);
        if (IS_ERR(port->wwan)) {
                err = PTR_ERR(port->wwan);
                goto err_free_port;
        }

        INIT_WORK(&port->del_work, wwan_hwsim_port_del_work);

        snprintf(name, sizeof(name), "port%u", port->id);
        port->debugfs_topdir = debugfs_create_dir(name, dev->debugfs_topdir);
        debugfs_create_file("destroy", 0200, port->debugfs_topdir, port,
                            &wwan_hwsim_debugfs_portdestroy_fops);

        return port;

err_free_port:
        kfree(port);

        return ERR_PTR(err);
}

static void wwan_hwsim_port_del(struct wwan_hwsim_port *port)
{
        debugfs_remove(port->debugfs_topdir);

        /* Make sure that there is no pending deletion work */
        if (current_work() != &port->del_work)
                cancel_work_sync(&port->del_work);

        wwan_remove_port(port->wwan);
        kfree(port);
}

static void wwan_hwsim_port_del_work(struct work_struct *work)
{
        struct wwan_hwsim_port *port =
                                container_of(work, typeof(*port), del_work);
        struct wwan_hwsim_dev *dev = port->dev;

        spin_lock(&dev->ports_lock);
        if (list_empty(&port->list)) {
                /* Someone else deleting port at the moment */
                spin_unlock(&dev->ports_lock);
                return;
        }
        list_del_init(&port->list);
        spin_unlock(&dev->ports_lock);

        wwan_hwsim_port_del(port);
}

static void wwan_hwsim_dev_release(struct device *sysdev)
{
        struct wwan_hwsim_dev *dev = container_of(sysdev, typeof(*dev), dev);

        kfree(dev);
}

static struct wwan_hwsim_dev *wwan_hwsim_dev_new(void)
{
        struct wwan_hwsim_dev *dev;
        int err;

        dev = kzalloc(sizeof(*dev), GFP_KERNEL);
        if (!dev)
                return ERR_PTR(-ENOMEM);

        spin_lock(&wwan_hwsim_devs_lock);
        dev->id = wwan_hwsim_dev_idx++;
        spin_unlock(&wwan_hwsim_devs_lock);

        dev->dev.release = wwan_hwsim_dev_release;
        dev->dev.class = wwan_hwsim_class;
        dev_set_name(&dev->dev, "hwsim%u", dev->id);

        spin_lock_init(&dev->ports_lock);
        INIT_LIST_HEAD(&dev->ports);

        err = device_register(&dev->dev);
        if (err)
                goto err_free_dev;

        INIT_WORK(&dev->del_work, wwan_hwsim_dev_del_work);

        err = wwan_register_ops(&dev->dev, &wwan_hwsim_wwan_rtnl_ops, dev, 1);
        if (err)
                goto err_unreg_dev;

        dev->debugfs_topdir = debugfs_create_dir(dev_name(&dev->dev),
                                                 wwan_hwsim_debugfs_topdir);
        debugfs_create_file("destroy", 0200, dev->debugfs_topdir, dev,
                            &wwan_hwsim_debugfs_devdestroy_fops);
        dev->debugfs_portcreate =
                debugfs_create_file("portcreate", 0200,
                                    dev->debugfs_topdir, dev,
                                    &wwan_hwsim_debugfs_portcreate_fops);

        return dev;

err_unreg_dev:
        device_unregister(&dev->dev);
        /* Memory will be freed in the device release callback */

        return ERR_PTR(err);

err_free_dev:
        kfree(dev);

        return ERR_PTR(err);
}

static void wwan_hwsim_dev_del(struct wwan_hwsim_dev *dev)
{
        debugfs_remove(dev->debugfs_portcreate);        /* Avoid new ports */

        spin_lock(&dev->ports_lock);
        while (!list_empty(&dev->ports)) {
                struct wwan_hwsim_port *port;

                port = list_first_entry(&dev->ports, struct wwan_hwsim_port,
                                        list);
                list_del_init(&port->list);
                spin_unlock(&dev->ports_lock);
                wwan_hwsim_port_del(port);
                spin_lock(&dev->ports_lock);
        }
        spin_unlock(&dev->ports_lock);

        debugfs_remove(dev->debugfs_topdir);

        /* This will remove all child netdev(s) */
        wwan_unregister_ops(&dev->dev);

        /* Make sure that there is no pending deletion work */
        if (current_work() != &dev->del_work)
                cancel_work_sync(&dev->del_work);

        device_unregister(&dev->dev);
        /* Memory will be freed in the device release callback */
}

static void wwan_hwsim_dev_del_work(struct work_struct *work)
{
        struct wwan_hwsim_dev *dev = container_of(work, typeof(*dev), del_work);

        spin_lock(&wwan_hwsim_devs_lock);
        if (list_empty(&dev->list)) {
                /* Someone else deleting device at the moment */
                spin_unlock(&wwan_hwsim_devs_lock);
                return;
        }
        list_del_init(&dev->list);
        spin_unlock(&wwan_hwsim_devs_lock);

        wwan_hwsim_dev_del(dev);
}

static ssize_t wwan_hwsim_debugfs_portdestroy_write(struct file *file,
                                                    const char __user *usrbuf,
                                                    size_t count, loff_t *ppos)
{
        struct wwan_hwsim_port *port = file->private_data;

        /* We can not delete port here since it will cause a deadlock due to
         * waiting this callback to finish in the debugfs_remove() call. So,
         * use workqueue.
         */
        schedule_work(&port->del_work);

        return count;
}

static const struct file_operations wwan_hwsim_debugfs_portdestroy_fops = {
        .write = wwan_hwsim_debugfs_portdestroy_write,
        .open = simple_open,
        .llseek = noop_llseek,
};

static ssize_t wwan_hwsim_debugfs_portcreate_write(struct file *file,
                                                   const char __user *usrbuf,
                                                   size_t count, loff_t *ppos)
{
        struct wwan_hwsim_dev *dev = file->private_data;
        struct wwan_hwsim_port *port;

        port = wwan_hwsim_port_new(dev);
        if (IS_ERR(port))
                return PTR_ERR(port);

        spin_lock(&dev->ports_lock);
        list_add_tail(&port->list, &dev->ports);
        spin_unlock(&dev->ports_lock);

        return count;
}

static const struct file_operations wwan_hwsim_debugfs_portcreate_fops = {
        .write = wwan_hwsim_debugfs_portcreate_write,
        .open = simple_open,
        .llseek = noop_llseek,
};

static ssize_t wwan_hwsim_debugfs_devdestroy_write(struct file *file,
                                                   const char __user *usrbuf,
                                                   size_t count, loff_t *ppos)
{
        struct wwan_hwsim_dev *dev = file->private_data;

        /* We can not delete device here since it will cause a deadlock due to
         * waiting this callback to finish in the debugfs_remove() call. So,
         * use workqueue.
         */
        schedule_work(&dev->del_work);

        return count;
}

static const struct file_operations wwan_hwsim_debugfs_devdestroy_fops = {
        .write = wwan_hwsim_debugfs_devdestroy_write,
        .open = simple_open,
        .llseek = noop_llseek,
};

static ssize_t wwan_hwsim_debugfs_devcreate_write(struct file *file,
                                                  const char __user *usrbuf,
                                                  size_t count, loff_t *ppos)
{
        struct wwan_hwsim_dev *dev;

        dev = wwan_hwsim_dev_new();
        if (IS_ERR(dev))
                return PTR_ERR(dev);

        spin_lock(&wwan_hwsim_devs_lock);
        list_add_tail(&dev->list, &wwan_hwsim_devs);
        spin_unlock(&wwan_hwsim_devs_lock);

        return count;
}

static const struct file_operations wwan_hwsim_debugfs_devcreate_fops = {
        .write = wwan_hwsim_debugfs_devcreate_write,
        .open = simple_open,
        .llseek = noop_llseek,
};

static int __init wwan_hwsim_init_devs(void)
{
        struct wwan_hwsim_dev *dev;
        int i, j;

        for (i = 0; i < wwan_hwsim_devsnum; ++i) {
                dev = wwan_hwsim_dev_new();
                if (IS_ERR(dev))
                        return PTR_ERR(dev);

                spin_lock(&wwan_hwsim_devs_lock);
                list_add_tail(&dev->list, &wwan_hwsim_devs);
                spin_unlock(&wwan_hwsim_devs_lock);

                /* Create a couple of ports per each device to accelerate
                 * the simulator readiness time.
                 */
                for (j = 0; j < 2; ++j) {
                        struct wwan_hwsim_port *port;

                        port = wwan_hwsim_port_new(dev);
                        if (IS_ERR(port))
                                return PTR_ERR(port);

                        spin_lock(&dev->ports_lock);
                        list_add_tail(&port->list, &dev->ports);
                        spin_unlock(&dev->ports_lock);
                }
        }

        return 0;
}

static void wwan_hwsim_free_devs(void)
{
        struct wwan_hwsim_dev *dev;

        spin_lock(&wwan_hwsim_devs_lock);
        while (!list_empty(&wwan_hwsim_devs)) {
                dev = list_first_entry(&wwan_hwsim_devs, struct wwan_hwsim_dev,
                                       list);
                list_del_init(&dev->list);
                spin_unlock(&wwan_hwsim_devs_lock);
                wwan_hwsim_dev_del(dev);
                spin_lock(&wwan_hwsim_devs_lock);
        }
        spin_unlock(&wwan_hwsim_devs_lock);
}

static int __init wwan_hwsim_init(void)
{
        int err;

        if (wwan_hwsim_devsnum < 0 || wwan_hwsim_devsnum > 128)
                return -EINVAL;

        wwan_hwsim_class = class_create(THIS_MODULE, "wwan_hwsim");
        if (IS_ERR(wwan_hwsim_class))
                return PTR_ERR(wwan_hwsim_class);

        wwan_hwsim_debugfs_topdir = debugfs_create_dir("wwan_hwsim", NULL);
        wwan_hwsim_debugfs_devcreate =
                        debugfs_create_file("devcreate", 0200,
                                            wwan_hwsim_debugfs_topdir, NULL,
                                            &wwan_hwsim_debugfs_devcreate_fops);

        err = wwan_hwsim_init_devs();
        if (err)
                goto err_clean_devs;

        return 0;

err_clean_devs:
        wwan_hwsim_free_devs();
        debugfs_remove(wwan_hwsim_debugfs_topdir);
        class_destroy(wwan_hwsim_class);

        return err;
}

static void __exit wwan_hwsim_exit(void)
{
        debugfs_remove(wwan_hwsim_debugfs_devcreate);   /* Avoid new devs */
        wwan_hwsim_free_devs();
        flush_scheduled_work();         /* Wait deletion works completion */
        debugfs_remove(wwan_hwsim_debugfs_topdir);
        class_destroy(wwan_hwsim_class);
}

module_init(wwan_hwsim_init);
module_exit(wwan_hwsim_exit);

MODULE_AUTHOR("Sergey Ryazanov");
MODULE_DESCRIPTION("Device simulator for WWAN framework");
MODULE_LICENSE("GPL");