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, 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
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.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
130static void __exit pps_tty_cleanup(void)
131{
132	tty_unregister_ldisc(&pps_ldisc_ops);
133}
134
135module_init(pps_tty_init);
136module_exit(pps_tty_cleanup);
137
138MODULE_ALIAS_LDISC(N_PPS);
139MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
140MODULE_DESCRIPTION("PPS TTY device driver");
141MODULE_LICENSE("GPL");
142