pps_gen_parport.c revision 46b402a0e5e4b4d81b11c32dfb2312bf5828ecb5 
1/*
2 * pps_gen_parport.c -- kernel parallel port PPS signal generator
3 *
4 *
5 * Copyright (C) 2009   Alexander Gordeev <lasaine@lvk.cs.msu.su>
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
20 */
21
22
23/*
24 * TODO:
25 * fix issues when realtime clock is adjusted in a leap
26 */
27
28#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
29
30#include <linux/kernel.h>
31#include <linux/module.h>
32#include <linux/init.h>
33#include <linux/time.h>
34#include <linux/hrtimer.h>
35#include <linux/parport.h>
36
37#define DRVDESC "parallel port PPS signal generator"
38
39#define SIGNAL		0
40#define NO_SIGNAL	PARPORT_CONTROL_STROBE
41
42/* module parameters */
43
44#define SEND_DELAY_MAX		100000
45
46static unsigned int send_delay = 30000;
47MODULE_PARM_DESC(delay,
48	"Delay between setting and dropping the signal (ns)");
49module_param_named(delay, send_delay, uint, 0);
50
51
52#define SAFETY_INTERVAL	3000	/* set the hrtimer earlier for safety (ns) */
53
54/* internal per port structure */
55struct pps_generator_pp {
56	struct pardevice *pardev;	/* parport device */
57	struct hrtimer timer;
58	long port_write_time;		/* calibrated port write time (ns) */
59};
60
61static struct pps_generator_pp device = {
62	.pardev = NULL,
63};
64
65static int attached;
66
67/* calibrated time between a hrtimer event and the reaction */
68static long hrtimer_error = SAFETY_INTERVAL;
69
70/* the kernel hrtimer event */
71static enum hrtimer_restart hrtimer_event(struct hrtimer *timer)
72{
73	struct timespec expire_time, ts1, ts2, ts3, dts;
74	struct pps_generator_pp *dev;
75	struct parport *port;
76	long lim, delta;
77	unsigned long flags;
78
79	/* NB: approx time with blocked interrupts =
80	   send_delay + 3 * SAFETY_INTERVAL */
81	local_irq_save(flags);
82
83	/* first of all we get the time stamp... */
84	getnstimeofday(&ts1);
85	expire_time = ktime_to_timespec(hrtimer_get_softexpires(timer));
86	dev = container_of(timer, struct pps_generator_pp, timer);
87	lim = NSEC_PER_SEC - send_delay - dev->port_write_time;
88
89	/* check if we are late */
90	if (expire_time.tv_sec != ts1.tv_sec || ts1.tv_nsec > lim) {
91		local_irq_restore(flags);
92		pr_err("we are late this time %ld.%09ld\n",
93				ts1.tv_sec, ts1.tv_nsec);
94		goto done;
95	}
96
97	/* busy loop until the time is right for an assert edge */
98	do {
99		getnstimeofday(&ts2);
100	} while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
101
102	/* set the signal */
103	port = dev->pardev->port;
104	port->ops->write_control(port, SIGNAL);
105
106	/* busy loop until the time is right for a clear edge */
107	lim = NSEC_PER_SEC - dev->port_write_time;
108	do {
109		getnstimeofday(&ts2);
110	} while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
111
112	/* unset the signal */
113	port->ops->write_control(port, NO_SIGNAL);
114
115	getnstimeofday(&ts3);
116
117	local_irq_restore(flags);
118
119	/* update calibrated port write time */
120	dts = timespec_sub(ts3, ts2);
121	dev->port_write_time =
122		(dev->port_write_time + timespec_to_ns(&dts)) >> 1;
123
124done:
125	/* update calibrated hrtimer error */
126	dts = timespec_sub(ts1, expire_time);
127	delta = timespec_to_ns(&dts);
128	/* If the new error value is bigger then the old, use the new
129	 * value, if not then slowly move towards the new value. This
130	 * way it should be safe in bad conditions and efficient in
131	 * good conditions.
132	 */
133	if (delta >= hrtimer_error)
134		hrtimer_error = delta;
135	else
136		hrtimer_error = (3 * hrtimer_error + delta) >> 2;
137
138	/* update the hrtimer expire time */
139	hrtimer_set_expires(timer,
140			ktime_set(expire_time.tv_sec + 1,
141				NSEC_PER_SEC - (send_delay +
142				dev->port_write_time + SAFETY_INTERVAL +
143				2 * hrtimer_error)));
144
145	return HRTIMER_RESTART;
146}
147
148/* calibrate port write time */
149#define PORT_NTESTS_SHIFT	5
150static void calibrate_port(struct pps_generator_pp *dev)
151{
152	struct parport *port = dev->pardev->port;
153	int i;
154	long acc = 0;
155
156	for (i = 0; i < (1 << PORT_NTESTS_SHIFT); i++) {
157		struct timespec a, b;
158		unsigned long irq_flags;
159
160		local_irq_save(irq_flags);
161		getnstimeofday(&a);
162		port->ops->write_control(port, NO_SIGNAL);
163		getnstimeofday(&b);
164		local_irq_restore(irq_flags);
165
166		b = timespec_sub(b, a);
167		acc += timespec_to_ns(&b);
168	}
169
170	dev->port_write_time = acc >> PORT_NTESTS_SHIFT;
171	pr_info("port write takes %ldns\n", dev->port_write_time);
172}
173
174static inline ktime_t next_intr_time(struct pps_generator_pp *dev)
175{
176	struct timespec ts;
177
178	getnstimeofday(&ts);
179
180	return ktime_set(ts.tv_sec +
181			((ts.tv_nsec > 990 * NSEC_PER_MSEC) ? 1 : 0),
182			NSEC_PER_SEC - (send_delay +
183			dev->port_write_time + 3 * SAFETY_INTERVAL));
184}
185
186static void parport_attach(struct parport *port)
187{
188	if (attached) {
189		/* we already have a port */
190		return;
191	}
192
193	device.pardev = parport_register_device(port, KBUILD_MODNAME,
194			NULL, NULL, NULL, 0, &device);
195	if (!device.pardev) {
196		pr_err("couldn't register with %s\n", port->name);
197		return;
198	}
199
200	if (parport_claim_or_block(device.pardev) < 0) {
201		pr_err("couldn't claim %s\n", port->name);
202		goto err_unregister_dev;
203	}
204
205	pr_info("attached to %s\n", port->name);
206	attached = 1;
207
208	calibrate_port(&device);
209
210	hrtimer_init(&device.timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
211	device.timer.function = hrtimer_event;
212#ifdef CONFIG_PREEMPT_RT
213	/* hrtimer interrupt will run in the interrupt context with this */
214	device.timer.irqsafe = 1;
215#endif
216
217	hrtimer_start(&device.timer, next_intr_time(&device), HRTIMER_MODE_ABS);
218
219	return;
220
221err_unregister_dev:
222	parport_unregister_device(device.pardev);
223}
224
225static void parport_detach(struct parport *port)
226{
227	if (port->cad != device.pardev)
228		return;	/* not our port */
229
230	hrtimer_cancel(&device.timer);
231	parport_release(device.pardev);
232	parport_unregister_device(device.pardev);
233}
234
235static struct parport_driver pps_gen_parport_driver = {
236	.name = KBUILD_MODNAME,
237	.attach = parport_attach,
238	.detach = parport_detach,
239};
240
241/* module staff */
242
243static int __init pps_gen_parport_init(void)
244{
245	int ret;
246
247	pr_info(DRVDESC "\n");
248
249	if (send_delay > SEND_DELAY_MAX) {
250		pr_err("delay value should be not greater"
251				" then %d\n", SEND_DELAY_MAX);
252		return -EINVAL;
253	}
254
255	ret = parport_register_driver(&pps_gen_parport_driver);
256	if (ret) {
257		pr_err("unable to register with parport\n");
258		return ret;
259	}
260
261	return  0;
262}
263
264static void __exit pps_gen_parport_exit(void)
265{
266	parport_unregister_driver(&pps_gen_parport_driver);
267	pr_info("hrtimer avg error is %ldns\n", hrtimer_error);
268}
269
270module_init(pps_gen_parport_init);
271module_exit(pps_gen_parport_exit);
272
273MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
274MODULE_DESCRIPTION(DRVDESC);
275MODULE_LICENSE("GPL");
276