1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * pps_parport.c -- kernel parallel port PPS client
4 *
5 * Copyright (C) 2009   Alexander Gordeev <lasaine@lvk.cs.msu.su>
6 */
7
8
9/*
10 * TODO:
11 * implement echo over SEL pin
12 */
13
14#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
15
16#include <linux/kernel.h>
17#include <linux/module.h>
18#include <linux/init.h>
19#include <linux/irqnr.h>
20#include <linux/time.h>
21#include <linux/slab.h>
22#include <linux/parport.h>
23#include <linux/pps_kernel.h>
24
25#define DRVDESC "parallel port PPS client"
26
27/* module parameters */
28
29#define CLEAR_WAIT_MAX		100
30#define CLEAR_WAIT_MAX_ERRORS	5
31
32static unsigned int clear_wait = 100;
33MODULE_PARM_DESC(clear_wait,
34	"Maximum number of port reads when polling for signal clear,"
35	" zero turns clear edge capture off entirely");
36module_param(clear_wait, uint, 0);
37
38static DEFINE_IDA(pps_client_index);
39
40/* internal per port structure */
41struct pps_client_pp {
42	struct pardevice *pardev;	/* parport device */
43	struct pps_device *pps;		/* PPS device */
44	unsigned int cw;		/* port clear timeout */
45	unsigned int cw_err;		/* number of timeouts */
46	int index;			/* device number */
47};
48
49static inline int signal_is_set(struct parport *port)
50{
51	return (port->ops->read_status(port) & PARPORT_STATUS_ACK) != 0;
52}
53
54/* parport interrupt handler */
55static void parport_irq(void *handle)
56{
57	struct pps_event_time ts_assert, ts_clear;
58	struct pps_client_pp *dev = handle;
59	struct parport *port = dev->pardev->port;
60	unsigned int i;
61	unsigned long flags;
62
63	/* first of all we get the time stamp... */
64	pps_get_ts(&ts_assert);
65
66	if (dev->cw == 0)
67		/* clear edge capture disabled */
68		goto out_assert;
69
70	/* try capture the clear edge */
71
72	/* We have to disable interrupts here. The idea is to prevent
73	 * other interrupts on the same processor to introduce random
74	 * lags while polling the port. Reading from IO port is known
75	 * to take approximately 1us while other interrupt handlers can
76	 * take much more potentially.
77	 *
78	 * Interrupts won't be disabled for a long time because the
79	 * number of polls is limited by clear_wait parameter which is
80	 * kept rather low. So it should never be an issue.
81	 */
82	local_irq_save(flags);
83	/* check the signal (no signal means the pulse is lost this time) */
84	if (!signal_is_set(port)) {
85		local_irq_restore(flags);
86		dev_err(dev->pps->dev, "lost the signal\n");
87		goto out_assert;
88	}
89
90	/* poll the port until the signal is unset */
91	for (i = dev->cw; i; i--)
92		if (!signal_is_set(port)) {
93			pps_get_ts(&ts_clear);
94			local_irq_restore(flags);
95			dev->cw_err = 0;
96			goto out_both;
97		}
98	local_irq_restore(flags);
99
100	/* timeout */
101	dev->cw_err++;
102	if (dev->cw_err >= CLEAR_WAIT_MAX_ERRORS) {
103		dev_err(dev->pps->dev, "disabled clear edge capture after %d"
104				" timeouts\n", dev->cw_err);
105		dev->cw = 0;
106		dev->cw_err = 0;
107	}
108
109out_assert:
110	/* fire assert event */
111	pps_event(dev->pps, &ts_assert,
112			PPS_CAPTUREASSERT, NULL);
113	return;
114
115out_both:
116	/* fire assert event */
117	pps_event(dev->pps, &ts_assert,
118			PPS_CAPTUREASSERT, NULL);
119	/* fire clear event */
120	pps_event(dev->pps, &ts_clear,
121			PPS_CAPTURECLEAR, NULL);
122	return;
123}
124
125static void parport_attach(struct parport *port)
126{
127	struct pardev_cb pps_client_cb;
128	int index;
129	struct pps_client_pp *device;
130	struct pps_source_info info = {
131		.name		= KBUILD_MODNAME,
132		.path		= "",
133		.mode		= PPS_CAPTUREBOTH | \
134				  PPS_OFFSETASSERT | PPS_OFFSETCLEAR | \
135				  PPS_ECHOASSERT | PPS_ECHOCLEAR | \
136				  PPS_CANWAIT | PPS_TSFMT_TSPEC,
137		.owner		= THIS_MODULE,
138		.dev		= NULL
139	};
140
141	device = kzalloc(sizeof(struct pps_client_pp), GFP_KERNEL);
142	if (!device) {
143		pr_err("memory allocation failed, not attaching\n");
144		return;
145	}
146
147	index = ida_simple_get(&pps_client_index, 0, 0, GFP_KERNEL);
148	memset(&pps_client_cb, 0, sizeof(pps_client_cb));
149	pps_client_cb.private = device;
150	pps_client_cb.irq_func = parport_irq;
151	pps_client_cb.flags = PARPORT_FLAG_EXCL;
152	device->pardev = parport_register_dev_model(port,
153						    KBUILD_MODNAME,
154						    &pps_client_cb,
155						    index);
156	if (!device->pardev) {
157		pr_err("couldn't register with %s\n", port->name);
158		goto err_free;
159	}
160
161	if (parport_claim_or_block(device->pardev) < 0) {
162		pr_err("couldn't claim %s\n", port->name);
163		goto err_unregister_dev;
164	}
165
166	device->pps = pps_register_source(&info,
167			PPS_CAPTUREBOTH | PPS_OFFSETASSERT | PPS_OFFSETCLEAR);
168	if (IS_ERR(device->pps)) {
169		pr_err("couldn't register PPS source\n");
170		goto err_release_dev;
171	}
172
173	device->cw = clear_wait;
174
175	port->ops->enable_irq(port);
176	device->index = index;
177
178	pr_info("attached to %s\n", port->name);
179
180	return;
181
182err_release_dev:
183	parport_release(device->pardev);
184err_unregister_dev:
185	parport_unregister_device(device->pardev);
186err_free:
187	ida_simple_remove(&pps_client_index, index);
188	kfree(device);
189}
190
191static void parport_detach(struct parport *port)
192{
193	struct pardevice *pardev = port->cad;
194	struct pps_client_pp *device;
195
196	/* FIXME: oooh, this is ugly! */
197	if (!pardev || strcmp(pardev->name, KBUILD_MODNAME))
198		/* not our port */
199		return;
200
201	device = pardev->private;
202
203	port->ops->disable_irq(port);
204	pps_unregister_source(device->pps);
205	parport_release(pardev);
206	parport_unregister_device(pardev);
207	ida_simple_remove(&pps_client_index, device->index);
208	kfree(device);
209}
210
211static struct parport_driver pps_parport_driver = {
212	.name = KBUILD_MODNAME,
213	.match_port = parport_attach,
214	.detach = parport_detach,
215	.devmodel = true,
216};
217
218/* module staff */
219
220static int __init pps_parport_init(void)
221{
222	int ret;
223
224	pr_info(DRVDESC "\n");
225
226	if (clear_wait > CLEAR_WAIT_MAX) {
227		pr_err("clear_wait value should be not greater"
228				" then %d\n", CLEAR_WAIT_MAX);
229		return -EINVAL;
230	}
231
232	ret = parport_register_driver(&pps_parport_driver);
233	if (ret) {
234		pr_err("unable to register with parport\n");
235		return ret;
236	}
237
238	return  0;
239}
240
241static void __exit pps_parport_exit(void)
242{
243	parport_unregister_driver(&pps_parport_driver);
244}
245
246module_init(pps_parport_init);
247module_exit(pps_parport_exit);
248
249MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
250MODULE_DESCRIPTION(DRVDESC);
251MODULE_LICENSE("GPL");
252