// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * pps-ldisc.c -- PPS line discipline
 *
 * Copyright (C) 2008   Rodolfo Giometti <giometti@linux.it>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/serial_core.h>
#include <linux/tty.h>
#include <linux/pps_kernel.h>
#include <linux/bug.h>

static void pps_tty_dcd_change(struct tty_struct *tty, bool active)
{
        struct pps_device *pps;
        struct pps_event_time ts;

        pps_get_ts(&ts);

        pps = pps_lookup_dev(tty);
        /*
         * This should never fail, but the ldisc locking is very
         * convoluted, so don't crash just in case.
         */
        if (WARN_ON_ONCE(pps == NULL))
                return;

        /* Now do the PPS event report */
        pps_event(pps, &ts, active ? PPS_CAPTUREASSERT :
                        PPS_CAPTURECLEAR, NULL);

        dev_dbg(&pps->dev, "PPS %s at %lu\n",
                        active ? "assert" : "clear", jiffies);
}

static int (*alias_n_tty_open)(struct tty_struct *tty);

static int pps_tty_open(struct tty_struct *tty)
{
        struct pps_source_info info;
        struct tty_driver *drv = tty->driver;
        int index = tty->index + drv->name_base;
        struct pps_device *pps;
        int ret;

        info.owner = THIS_MODULE;
        info.dev = NULL;
        snprintf(info.name, PPS_MAX_NAME_LEN, "%s%d", drv->driver_name, index);
        snprintf(info.path, PPS_MAX_NAME_LEN, "/dev/%s%d", drv->name, index);
        info.mode = PPS_CAPTUREBOTH | \
                        PPS_OFFSETASSERT | PPS_OFFSETCLEAR | \
                        PPS_CANWAIT | PPS_TSFMT_TSPEC;

        pps = pps_register_source(&info, PPS_CAPTUREBOTH | \
                                PPS_OFFSETASSERT | PPS_OFFSETCLEAR);
        if (IS_ERR(pps)) {
                pr_err("cannot register PPS source \"%s\"\n", info.path);
                return PTR_ERR(pps);
        }
        pps->lookup_cookie = tty;

        /* Now open the base class N_TTY ldisc */
        ret = alias_n_tty_open(tty);
        if (ret < 0) {
                pr_err("cannot open tty ldisc \"%s\"\n", info.path);
                goto err_unregister;
        }

        dev_dbg(&pps->dev, "source \"%s\" added\n", info.path);

        return 0;

err_unregister:
        pps_unregister_source(pps);
        return ret;
}

static void (*alias_n_tty_close)(struct tty_struct *tty);

static void pps_tty_close(struct tty_struct *tty)
{
        struct pps_device *pps = pps_lookup_dev(tty);

        alias_n_tty_close(tty);

        if (WARN_ON(!pps))
                return;

        dev_info(&pps->dev, "removed\n");
        pps_unregister_source(pps);
}

static struct tty_ldisc_ops pps_ldisc_ops;

/*
 * Module stuff
 */

static int __init pps_tty_init(void)
{
        int err;

        /* Inherit the N_TTY's ops */
        n_tty_inherit_ops(&pps_ldisc_ops);

        /* Save N_TTY's open()/close() methods */
        alias_n_tty_open = pps_ldisc_ops.open;
        alias_n_tty_close = pps_ldisc_ops.close;

        /* Init PPS_TTY data */
        pps_ldisc_ops.owner = THIS_MODULE;
        pps_ldisc_ops.num = N_PPS;
        pps_ldisc_ops.name = "pps_tty";
        pps_ldisc_ops.dcd_change = pps_tty_dcd_change;
        pps_ldisc_ops.open = pps_tty_open;
        pps_ldisc_ops.close = pps_tty_close;

        err = tty_register_ldisc(&pps_ldisc_ops);
        if (err)
                pr_err("can't register PPS line discipline\n");
        else
                pr_info("PPS line discipline registered\n");

        return err;
}

static void __exit pps_tty_cleanup(void)
{
        tty_unregister_ldisc(&pps_ldisc_ops);
}

module_init(pps_tty_init);
module_exit(pps_tty_cleanup);

MODULE_ALIAS_LDISC(N_PPS);
MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
MODULE_DESCRIPTION("PPS TTY device driver");
MODULE_LICENSE("GPL");