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
18static 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
41static int (*alias_n_tty_open)(struct tty_struct *tty);
42
43static 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
78err_unregister:
79	pps_unregister_source(pps);
80	return ret;
81}
82
83static void (*alias_n_tty_close)(struct tty_struct *tty);
84
85static 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
98static struct tty_ldisc_ops pps_ldisc_ops;
99
100/*
101 * Module stuff
102 */
103
104static 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
132static 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
143module_init(pps_tty_init);
144module_exit(pps_tty_cleanup);
145
146MODULE_ALIAS_LDISC(N_PPS);
147MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
148MODULE_DESCRIPTION("PPS TTY device driver");
149MODULE_LICENSE("GPL");
150