drivers/pps/clients/pps-ldisc.c

   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
  16 static void pps_tty_dcd_change(struct tty_struct *tty, bool active)
  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, active ? PPS_CAPTUREASSERT :
  33                         PPS_CAPTURECLEAR, NULL);
  34
  35         dev_dbg(pps->dev, "PPS %s at %lu\n",
  36                         active ? "assert" : "clear", jiffies);
  37 }
  38
  39 static int (*alias_n_tty_open)(struct tty_struct *tty);
  40
  41 static 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
  76 err_unregister:
  77         pps_unregister_source(pps);
  78         return ret;
  79 }
  80
  81 static void (*alias_n_tty_close)(struct tty_struct *tty);
  82
  83 static 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
  96 static struct tty_ldisc_ops pps_ldisc_ops;
  97
  98 /*
  99  * Module stuff
 100  */
 101
 102 static 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.num = N_PPS;
 116         pps_ldisc_ops.name = "pps_tty";
 117         pps_ldisc_ops.dcd_change = pps_tty_dcd_change;
 118         pps_ldisc_ops.open = pps_tty_open;
 119         pps_ldisc_ops.close = pps_tty_close;
 120
 121         err = tty_register_ldisc(&pps_ldisc_ops);
 122         if (err)
 123                 pr_err("can't register PPS line discipline\n");
 124         else
 125                 pr_info("PPS line discipline registered\n");
 126
 127         return err;
 128 }
 129
 130 static void __exit pps_tty_cleanup(void)
 131 {
 132         tty_unregister_ldisc(&pps_ldisc_ops);
 133 }
 134
 135 module_init(pps_tty_init);
 136 module_exit(pps_tty_cleanup);
 137
 138 MODULE_ALIAS_LDISC(N_PPS);
 139 MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
 140 MODULE_DESCRIPTION("PPS TTY device driver");
 141 MODULE_LICENSE("GPL");