pps-ldisc.c

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/*
 * pps-ldisc.c -- PPS line discipline
 *
 *
 * Copyright (C) 2008   Rodolfo Giometti <[email protected]>
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#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>

#define PPS_TTY_MAGIC       0x0001

static void pps_tty_dcd_change(struct tty_struct *tty, unsigned int status,
                struct pps_event_time *ts)
{
    struct pps_device *pps = (struct pps_device *)tty->disc_data;

    BUG_ON(pps == NULL);

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

    dev_dbg(pps->dev, "PPS %s at %lu\n",
            status ? "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 (pps == NULL) {
        pr_err("cannot register PPS source \"%s\"\n", info.path);
        return -ENOMEM;
    }
    tty->disc_data = pps;

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

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

    return 0;

err_unregister:
    tty->disc_data = NULL;
    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 = (struct pps_device *)tty->disc_data;

    alias_n_tty_close(tty);

    tty->disc_data = NULL;
    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.magic = PPS_TTY_MAGIC;
    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(N_PPS, &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)
{
    int err;

    err = tty_unregister_ldisc(N_PPS);
    if (err)
        pr_err("can't unregister PPS line discipline\n");
    else
        pr_info("PPS line discipline removed\n");
}

module_init(pps_tty_init);
module_exit(pps_tty_cleanup);

MODULE_ALIAS_LDISC(N_PPS);
MODULE_AUTHOR("Rodolfo Giometti <[email protected]>");
MODULE_DESCRIPTION("PPS TTY device driver");
MODULE_LICENSE("GPL");