// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2021 STMicroelectronics - All Rights Reserved
 *
 * The rpmsg tty driver implements serial communication on the RPMsg bus to makes
 * possible for user-space programs to send and receive rpmsg messages as a standard
 * tty protocol.
 *
 * The remote processor can instantiate a new tty by requesting a "rpmsg-tty" RPMsg service.
 * The "rpmsg-tty" service is directly used for data exchange. No flow control is implemented yet.
 */

#define pr_fmt(fmt)             KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/rpmsg.h>
#include <linux/slab.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>

#define RPMSG_TTY_NAME  "ttyRPMSG"
#define MAX_TTY_RPMSG   32

static DEFINE_IDR(tty_idr);     /* tty instance id */
static DEFINE_MUTEX(idr_lock);  /* protects tty_idr */

static struct tty_driver *rpmsg_tty_driver;

struct rpmsg_tty_port {
        struct tty_port         port;    /* TTY port data */
        int                     id;      /* TTY rpmsg index */
        struct rpmsg_device     *rpdev;  /* rpmsg device */
};

static int rpmsg_tty_cb(struct rpmsg_device *rpdev, void *data, int len, void *priv, u32 src)
{
        struct rpmsg_tty_port *cport = dev_get_drvdata(&rpdev->dev);
        int copied;

        if (!len)
                return -EINVAL;
        copied = tty_insert_flip_string(&cport->port, data, len);
        if (copied != len)
                dev_err_ratelimited(&rpdev->dev, "Trunc buffer: available space is %d\n", copied);
        tty_flip_buffer_push(&cport->port);

        return 0;
}

static int rpmsg_tty_install(struct tty_driver *driver, struct tty_struct *tty)
{
        struct rpmsg_tty_port *cport = idr_find(&tty_idr, tty->index);
        struct tty_port *port;

        tty->driver_data = cport;

        port = tty_port_get(&cport->port);
        return tty_port_install(port, driver, tty);
}

static void rpmsg_tty_cleanup(struct tty_struct *tty)
{
        tty_port_put(tty->port);
}

static int rpmsg_tty_open(struct tty_struct *tty, struct file *filp)
{
        return tty_port_open(tty->port, tty, filp);
}

static void rpmsg_tty_close(struct tty_struct *tty, struct file *filp)
{
        return tty_port_close(tty->port, tty, filp);
}

static ssize_t rpmsg_tty_write(struct tty_struct *tty, const u8 *buf,
                               size_t len)
{
        struct rpmsg_tty_port *cport = tty->driver_data;
        struct rpmsg_device *rpdev;
        int msg_max_size, msg_size;
        int ret;

        rpdev = cport->rpdev;

        msg_max_size = rpmsg_get_mtu(rpdev->ept);
        if (msg_max_size < 0)
                return msg_max_size;

        msg_size = min_t(unsigned int, len, msg_max_size);

        /*
         * Use rpmsg_trysend instead of rpmsg_send to send the message so the caller is not
         * hung until a rpmsg buffer is available. In such case rpmsg_trysend returns -ENOMEM.
         */
        ret = rpmsg_trysend(rpdev->ept, (void *)buf, msg_size);
        if (ret) {
                dev_dbg_ratelimited(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
                return ret;
        }

        return msg_size;
}

static unsigned int rpmsg_tty_write_room(struct tty_struct *tty)
{
        struct rpmsg_tty_port *cport = tty->driver_data;
        int size;

        size = rpmsg_get_mtu(cport->rpdev->ept);
        if (size < 0)
                return 0;

        return size;
}

static void rpmsg_tty_hangup(struct tty_struct *tty)
{
        tty_port_hangup(tty->port);
}

static const struct tty_operations rpmsg_tty_ops = {
        .install        = rpmsg_tty_install,
        .open           = rpmsg_tty_open,
        .close          = rpmsg_tty_close,
        .write          = rpmsg_tty_write,
        .write_room     = rpmsg_tty_write_room,
        .hangup         = rpmsg_tty_hangup,
        .cleanup        = rpmsg_tty_cleanup,
};

static struct rpmsg_tty_port *rpmsg_tty_alloc_cport(void)
{
        struct rpmsg_tty_port *cport;
        int ret;

        cport = kzalloc_obj(*cport);
        if (!cport)
                return ERR_PTR(-ENOMEM);

        mutex_lock(&idr_lock);
        ret = idr_alloc(&tty_idr, cport, 0, MAX_TTY_RPMSG, GFP_KERNEL);
        mutex_unlock(&idr_lock);

        if (ret < 0) {
                kfree(cport);
                return ERR_PTR(ret);
        }

        cport->id = ret;

        return cport;
}

static void rpmsg_tty_destruct_port(struct tty_port *port)
{
        struct rpmsg_tty_port *cport = container_of(port, struct rpmsg_tty_port, port);

        mutex_lock(&idr_lock);
        idr_remove(&tty_idr, cport->id);
        mutex_unlock(&idr_lock);

        kfree(cport);
}

static const struct tty_port_operations rpmsg_tty_port_ops = {
        .destruct = rpmsg_tty_destruct_port,
};


static int rpmsg_tty_probe(struct rpmsg_device *rpdev)
{
        struct rpmsg_tty_port *cport;
        struct device *dev = &rpdev->dev;
        struct device *tty_dev;
        int ret;

        cport = rpmsg_tty_alloc_cport();
        if (IS_ERR(cport))
                return dev_err_probe(dev, PTR_ERR(cport), "Failed to alloc tty port\n");

        tty_port_init(&cport->port);
        cport->port.ops = &rpmsg_tty_port_ops;

        tty_dev = tty_port_register_device(&cport->port, rpmsg_tty_driver,
                                           cport->id, dev);
        if (IS_ERR(tty_dev)) {
                ret = dev_err_probe(dev, PTR_ERR(tty_dev), "Failed to register tty port\n");
                tty_port_put(&cport->port);
                return ret;
        }

        cport->rpdev = rpdev;

        dev_set_drvdata(dev, cport);

        dev_dbg(dev, "New channel: 0x%x -> 0x%x: " RPMSG_TTY_NAME "%d\n",
                rpdev->src, rpdev->dst, cport->id);

        return 0;
}

static void rpmsg_tty_remove(struct rpmsg_device *rpdev)
{
        struct rpmsg_tty_port *cport = dev_get_drvdata(&rpdev->dev);

        dev_dbg(&rpdev->dev, "Removing rpmsg tty device %d\n", cport->id);

        /* User hang up to release the tty */
        tty_port_tty_hangup(&cport->port, false);

        tty_unregister_device(rpmsg_tty_driver, cport->id);

        tty_port_put(&cport->port);
}

static struct rpmsg_device_id rpmsg_driver_tty_id_table[] = {
        { .name = "rpmsg-tty" },
        { },
};
MODULE_DEVICE_TABLE(rpmsg, rpmsg_driver_tty_id_table);

static struct rpmsg_driver rpmsg_tty_rpmsg_drv = {
        .drv.name       = KBUILD_MODNAME,
        .id_table       = rpmsg_driver_tty_id_table,
        .probe          = rpmsg_tty_probe,
        .callback       = rpmsg_tty_cb,
        .remove         = rpmsg_tty_remove,
};

static int __init rpmsg_tty_init(void)
{
        int ret;

        rpmsg_tty_driver = tty_alloc_driver(MAX_TTY_RPMSG, TTY_DRIVER_REAL_RAW |
                                            TTY_DRIVER_DYNAMIC_DEV);
        if (IS_ERR(rpmsg_tty_driver))
                return PTR_ERR(rpmsg_tty_driver);

        rpmsg_tty_driver->driver_name = "rpmsg_tty";
        rpmsg_tty_driver->name = RPMSG_TTY_NAME;
        rpmsg_tty_driver->major = 0;
        rpmsg_tty_driver->type = TTY_DRIVER_TYPE_CONSOLE;

        /* Disable unused mode by default */
        rpmsg_tty_driver->init_termios = tty_std_termios;
        rpmsg_tty_driver->init_termios.c_lflag &= ~(ECHO | ICANON);
        rpmsg_tty_driver->init_termios.c_oflag &= ~(OPOST | ONLCR);

        tty_set_operations(rpmsg_tty_driver, &rpmsg_tty_ops);

        ret = tty_register_driver(rpmsg_tty_driver);
        if (ret < 0) {
                pr_err("Couldn't install driver: %d\n", ret);
                goto error_put;
        }

        ret = register_rpmsg_driver(&rpmsg_tty_rpmsg_drv);
        if (ret < 0) {
                pr_err("Couldn't register driver: %d\n", ret);
                goto error_unregister;
        }

        return 0;

error_unregister:
        tty_unregister_driver(rpmsg_tty_driver);

error_put:
        tty_driver_kref_put(rpmsg_tty_driver);

        return ret;
}

static void __exit rpmsg_tty_exit(void)
{
        unregister_rpmsg_driver(&rpmsg_tty_rpmsg_drv);
        tty_unregister_driver(rpmsg_tty_driver);
        tty_driver_kref_put(rpmsg_tty_driver);
        idr_destroy(&tty_idr);
}

module_init(rpmsg_tty_init);
module_exit(rpmsg_tty_exit);

MODULE_AUTHOR("Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>");
MODULE_DESCRIPTION("remote processor messaging tty driver");
MODULE_LICENSE("GPL v2");