linux/drivers/pps/clients/pps-ldisc.c
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   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * pps-ldisc.c -- PPS line discipline
   4 *
   5 * Copyright (C) 2008   Rodolfo Giometti <giometti@linux.it>
   6 */
   7
   8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   9
  10#include <linux/module.h>
  11#include <linux/serial_core.h>
  12#include <linux/tty.h>
  13#include <linux/pps_kernel.h>
  14#include <linux/bug.h>
  15
  16static void pps_tty_dcd_change(struct tty_struct *tty, unsigned int status)
  17{
  18        struct pps_device *pps;
  19        struct pps_event_time ts;
  20
  21        pps_get_ts(&ts);
  22
  23        pps = pps_lookup_dev(tty);
  24        /*
  25         * This should never fail, but the ldisc locking is very
  26         * convoluted, so don't crash just in case.
  27         */
  28        if (WARN_ON_ONCE(pps == NULL))
  29                return;
  30
  31        /* Now do the PPS event report */
  32        pps_event(pps, &ts, status ? PPS_CAPTUREASSERT :
  33                        PPS_CAPTURECLEAR, NULL);
  34
  35        dev_dbg(pps->dev, "PPS %s at %lu\n",
  36                        status ? "assert" : "clear", jiffies);
  37}
  38
  39static int (*alias_n_tty_open)(struct tty_struct *tty);
  40
  41static int pps_tty_open(struct tty_struct *tty)
  42{
  43        struct pps_source_info info;
  44        struct tty_driver *drv = tty->driver;
  45        int index = tty->index + drv->name_base;
  46        struct pps_device *pps;
  47        int ret;
  48
  49        info.owner = THIS_MODULE;
  50        info.dev = NULL;
  51        snprintf(info.name, PPS_MAX_NAME_LEN, "%s%d", drv->driver_name, index);
  52        snprintf(info.path, PPS_MAX_NAME_LEN, "/dev/%s%d", drv->name, index);
  53        info.mode = PPS_CAPTUREBOTH | \
  54                        PPS_OFFSETASSERT | PPS_OFFSETCLEAR | \
  55                        PPS_CANWAIT | PPS_TSFMT_TSPEC;
  56
  57        pps = pps_register_source(&info, PPS_CAPTUREBOTH | \
  58                                PPS_OFFSETASSERT | PPS_OFFSETCLEAR);
  59        if (IS_ERR(pps)) {
  60                pr_err("cannot register PPS source \"%s\"\n", info.path);
  61                return PTR_ERR(pps);
  62        }
  63        pps->lookup_cookie = tty;
  64
  65        /* Now open the base class N_TTY ldisc */
  66        ret = alias_n_tty_open(tty);
  67        if (ret < 0) {
  68                pr_err("cannot open tty ldisc \"%s\"\n", info.path);
  69                goto err_unregister;
  70        }
  71
  72        dev_info(pps->dev, "source \"%s\" added\n", info.path);
  73
  74        return 0;
  75
  76err_unregister:
  77        pps_unregister_source(pps);
  78        return ret;
  79}
  80
  81static void (*alias_n_tty_close)(struct tty_struct *tty);
  82
  83static void pps_tty_close(struct tty_struct *tty)
  84{
  85        struct pps_device *pps = pps_lookup_dev(tty);
  86
  87        alias_n_tty_close(tty);
  88
  89        if (WARN_ON(!pps))
  90                return;
  91
  92        dev_info(pps->dev, "removed\n");
  93        pps_unregister_source(pps);
  94}
  95
  96static struct tty_ldisc_ops pps_ldisc_ops;
  97
  98/*
  99 * Module stuff
 100 */
 101
 102static int __init pps_tty_init(void)
 103{
 104        int err;
 105
 106        /* Inherit the N_TTY's ops */
 107        n_tty_inherit_ops(&pps_ldisc_ops);
 108
 109        /* Save N_TTY's open()/close() methods */
 110        alias_n_tty_open = pps_ldisc_ops.open;
 111        alias_n_tty_close = pps_ldisc_ops.close;
 112
 113        /* Init PPS_TTY data */
 114        pps_ldisc_ops.owner = THIS_MODULE;
 115        pps_ldisc_ops.name = "pps_tty";
 116        pps_ldisc_ops.dcd_change = pps_tty_dcd_change;
 117        pps_ldisc_ops.open = pps_tty_open;
 118        pps_ldisc_ops.close = pps_tty_close;
 119
 120        err = tty_register_ldisc(N_PPS, &pps_ldisc_ops);
 121        if (err)
 122                pr_err("can't register PPS line discipline\n");
 123        else
 124                pr_info("PPS line discipline registered\n");
 125
 126        return err;
 127}
 128
 129static void __exit pps_tty_cleanup(void)
 130{
 131        int err;
 132
 133        err = tty_unregister_ldisc(N_PPS);
 134        if (err)
 135                pr_err("can't unregister PPS line discipline\n");
 136        else
 137                pr_info("PPS line discipline removed\n");
 138}
 139
 140module_init(pps_tty_init);
 141module_exit(pps_tty_cleanup);
 142
 143MODULE_ALIAS_LDISC(N_PPS);
 144MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
 145MODULE_DESCRIPTION("PPS TTY device driver");
 146MODULE_LICENSE("GPL");
 147