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 #define PPS_TTY_MAGIC           0x0001
  17
  18 static void pps_tty_dcd_change(struct tty_struct *tty, unsigned int status)
  19 {
  20         struct pps_device *pps;
  21         struct pps_event_time ts;
  22
  23         pps_get_ts(&ts);
  24
  25         pps = pps_lookup_dev(tty);
  26         /*
  27          * This should never fail, but the ldisc locking is very
  28          * convoluted, so don't crash just in case.
  29          */
  30         if (WARN_ON_ONCE(pps == NULL))
  31                 return;
  32
  33         /* Now do the PPS event report */
  34         pps_event(pps, &ts, status ? PPS_CAPTUREASSERT :
  35                         PPS_CAPTURECLEAR, NULL);
  36
  37         dev_dbg(pps->dev, "PPS %s at %lu\n",
  38                         status ? "assert" : "clear", jiffies);
  39 }
  40
  41 static int (*alias_n_tty_open)(struct tty_struct *tty);
  42
  43 static int pps_tty_open(struct tty_struct *tty)
  44 {
  45         struct pps_source_info info;
  46         struct tty_driver *drv = tty->driver;
  47         int index = tty->index + drv->name_base;
  48         struct pps_device *pps;
  49         int ret;
  50
  51         info.owner = THIS_MODULE;
  52         info.dev = NULL;
  53         snprintf(info.name, PPS_MAX_NAME_LEN, "%s%d", drv->driver_name, index);
  54         snprintf(info.path, PPS_MAX_NAME_LEN, "/dev/%s%d", drv->name, index);
  55         info.mode = PPS_CAPTUREBOTH | \
  56                         PPS_OFFSETASSERT | PPS_OFFSETCLEAR | \
  57                         PPS_CANWAIT | PPS_TSFMT_TSPEC;
  58
  59         pps = pps_register_source(&info, PPS_CAPTUREBOTH | \
  60                                 PPS_OFFSETASSERT | PPS_OFFSETCLEAR);
  61         if (IS_ERR(pps)) {
  62                 pr_err("cannot register PPS source \"%s\"\n", info.path);
  63                 return PTR_ERR(pps);
  64         }
  65         pps->lookup_cookie = tty;
  66
  67         /* Now open the base class N_TTY ldisc */
  68         ret = alias_n_tty_open(tty);
  69         if (ret < 0) {
  70                 pr_err("cannot open tty ldisc \"%s\"\n", info.path);
  71                 goto err_unregister;
  72         }
  73
  74         dev_info(pps->dev, "source \"%s\" added\n", info.path);
  75
  76         return 0;
  77
  78 err_unregister:
  79         pps_unregister_source(pps);
  80         return ret;
  81 }
  82
  83 static void (*alias_n_tty_close)(struct tty_struct *tty);
  84
  85 static void pps_tty_close(struct tty_struct *tty)
  86 {
  87         struct pps_device *pps = pps_lookup_dev(tty);
  88
  89         alias_n_tty_close(tty);
  90
  91         if (WARN_ON(!pps))
  92                 return;
  93
  94         dev_info(pps->dev, "removed\n");
  95         pps_unregister_source(pps);
  96 }
  97
  98 static struct tty_ldisc_ops pps_ldisc_ops;
  99
 100 /*
 101  * Module stuff
 102  */
 103
 104 static int __init pps_tty_init(void)
 105 {
 106         int err;
 107
 108         /* Inherit the N_TTY's ops */
 109         n_tty_inherit_ops(&pps_ldisc_ops);
 110
 111         /* Save N_TTY's open()/close() methods */
 112         alias_n_tty_open = pps_ldisc_ops.open;
 113         alias_n_tty_close = pps_ldisc_ops.close;
 114
 115         /* Init PPS_TTY data */
 116         pps_ldisc_ops.owner = THIS_MODULE;
 117         pps_ldisc_ops.magic = PPS_TTY_MAGIC;
 118         pps_ldisc_ops.name = "pps_tty";
 119         pps_ldisc_ops.dcd_change = pps_tty_dcd_change;
 120         pps_ldisc_ops.open = pps_tty_open;
 121         pps_ldisc_ops.close = pps_tty_close;
 122
 123         err = tty_register_ldisc(N_PPS, &pps_ldisc_ops);
 124         if (err)
 125                 pr_err("can't register PPS line discipline\n");
 126         else
 127                 pr_info("PPS line discipline registered\n");
 128
 129         return err;
 130 }
 131
 132 static void __exit pps_tty_cleanup(void)
 133 {
 134         int err;
 135
 136         err = tty_unregister_ldisc(N_PPS);
 137         if (err)
 138                 pr_err("can't unregister PPS line discipline\n");
 139         else
 140                 pr_info("PPS line discipline removed\n");
 141 }
 142
 143 module_init(pps_tty_init);
 144 module_exit(pps_tty_cleanup);
 145
 146 MODULE_ALIAS_LDISC(N_PPS);
 147 MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
 148 MODULE_DESCRIPTION("PPS TTY device driver");
 149 MODULE_LICENSE("GPL");