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1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * pps_gen_parport.c -- kernel parallel port PPS signal generator
4 *
5 * Copyright (C) 2009 Alexander Gordeev <lasaine@lvk.cs.msu.su>
6 */
7
8
9/*
10 * TODO:
11 * fix issues when realtime clock is adjusted in a leap
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/time.h>
20#include <linux/hrtimer.h>
21#include <linux/parport.h>
22
23#define SIGNAL 0
24#define NO_SIGNAL PARPORT_CONTROL_STROBE
25
26/* module parameters */
27
28#define SEND_DELAY_MAX 100000
29
30static unsigned int send_delay = 30000;
31MODULE_PARM_DESC(delay,
32 "Delay between setting and dropping the signal (ns)");
33module_param_named(delay, send_delay, uint, 0);
34
35
36#define SAFETY_INTERVAL 3000 /* set the hrtimer earlier for safety (ns) */
37
38/* internal per port structure */
39struct pps_generator_pp {
40 struct pardevice *pardev; /* parport device */
41 struct hrtimer timer;
42 long port_write_time; /* calibrated port write time (ns) */
43};
44
45static struct pps_generator_pp device = {
46 .pardev = NULL,
47};
48
49static int attached;
50
51/* calibrated time between a hrtimer event and the reaction */
52static long hrtimer_error = SAFETY_INTERVAL;
53
54/* the kernel hrtimer event */
55static enum hrtimer_restart hrtimer_event(struct hrtimer *timer)
56{
57 struct timespec64 expire_time, ts1, ts2, ts3, dts;
58 struct pps_generator_pp *dev;
59 struct parport *port;
60 long lim, delta;
61 unsigned long flags;
62
63 /* We have to disable interrupts here. The idea is to prevent
64 * other interrupts on the same processor to introduce random
65 * lags while polling the clock. ktime_get_real_ts64() takes <1us on
66 * most machines while other interrupt handlers can take much
67 * more potentially.
68 *
69 * NB: approx time with blocked interrupts =
70 * send_delay + 3 * SAFETY_INTERVAL
71 */
72 local_irq_save(flags);
73
74 /* first of all we get the time stamp... */
75 ktime_get_real_ts64(&ts1);
76 expire_time = ktime_to_timespec64(hrtimer_get_softexpires(timer));
77 dev = container_of(timer, struct pps_generator_pp, timer);
78 lim = NSEC_PER_SEC - send_delay - dev->port_write_time;
79
80 /* check if we are late */
81 if (expire_time.tv_sec != ts1.tv_sec || ts1.tv_nsec > lim) {
82 local_irq_restore(flags);
83 pr_err("we are late this time %lld.%09ld\n",
84 (s64)ts1.tv_sec, ts1.tv_nsec);
85 goto done;
86 }
87
88 /* busy loop until the time is right for an assert edge */
89 do {
90 ktime_get_real_ts64(&ts2);
91 } while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
92
93 /* set the signal */
94 port = dev->pardev->port;
95 port->ops->write_control(port, SIGNAL);
96
97 /* busy loop until the time is right for a clear edge */
98 lim = NSEC_PER_SEC - dev->port_write_time;
99 do {
100 ktime_get_real_ts64(&ts2);
101 } while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
102
103 /* unset the signal */
104 port->ops->write_control(port, NO_SIGNAL);
105
106 ktime_get_real_ts64(&ts3);
107
108 local_irq_restore(flags);
109
110 /* update calibrated port write time */
111 dts = timespec64_sub(ts3, ts2);
112 dev->port_write_time =
113 (dev->port_write_time + timespec64_to_ns(&dts)) >> 1;
114
115done:
116 /* update calibrated hrtimer error */
117 dts = timespec64_sub(ts1, expire_time);
118 delta = timespec64_to_ns(&dts);
119 /* If the new error value is bigger then the old, use the new
120 * value, if not then slowly move towards the new value. This
121 * way it should be safe in bad conditions and efficient in
122 * good conditions.
123 */
124 if (delta >= hrtimer_error)
125 hrtimer_error = delta;
126 else
127 hrtimer_error = (3 * hrtimer_error + delta) >> 2;
128
129 /* update the hrtimer expire time */
130 hrtimer_set_expires(timer,
131 ktime_set(expire_time.tv_sec + 1,
132 NSEC_PER_SEC - (send_delay +
133 dev->port_write_time + SAFETY_INTERVAL +
134 2 * hrtimer_error)));
135
136 return HRTIMER_RESTART;
137}
138
139/* calibrate port write time */
140#define PORT_NTESTS_SHIFT 5
141static void calibrate_port(struct pps_generator_pp *dev)
142{
143 struct parport *port = dev->pardev->port;
144 int i;
145 long acc = 0;
146
147 for (i = 0; i < (1 << PORT_NTESTS_SHIFT); i++) {
148 struct timespec64 a, b;
149 unsigned long irq_flags;
150
151 local_irq_save(irq_flags);
152 ktime_get_real_ts64(&a);
153 port->ops->write_control(port, NO_SIGNAL);
154 ktime_get_real_ts64(&b);
155 local_irq_restore(irq_flags);
156
157 b = timespec64_sub(b, a);
158 acc += timespec64_to_ns(&b);
159 }
160
161 dev->port_write_time = acc >> PORT_NTESTS_SHIFT;
162 pr_info("port write takes %ldns\n", dev->port_write_time);
163}
164
165static inline ktime_t next_intr_time(struct pps_generator_pp *dev)
166{
167 struct timespec64 ts;
168
169 ktime_get_real_ts64(&ts);
170
171 return ktime_set(ts.tv_sec +
172 ((ts.tv_nsec > 990 * NSEC_PER_MSEC) ? 1 : 0),
173 NSEC_PER_SEC - (send_delay +
174 dev->port_write_time + 3 * SAFETY_INTERVAL));
175}
176
177static void parport_attach(struct parport *port)
178{
179 struct pardev_cb pps_cb;
180
181 if (send_delay > SEND_DELAY_MAX) {
182 pr_err("delay value should be not greater then %d\n", SEND_DELAY_MAX);
183 return;
184 }
185
186 if (attached) {
187 /* we already have a port */
188 return;
189 }
190
191 memset(&pps_cb, 0, sizeof(pps_cb));
192 pps_cb.private = &device;
193 pps_cb.flags = PARPORT_FLAG_EXCL;
194 device.pardev = parport_register_dev_model(port, KBUILD_MODNAME,
195 &pps_cb, 0);
196 if (!device.pardev) {
197 pr_err("couldn't register with %s\n", port->name);
198 return;
199 }
200
201 if (parport_claim_or_block(device.pardev) < 0) {
202 pr_err("couldn't claim %s\n", port->name);
203 goto err_unregister_dev;
204 }
205
206 pr_info("attached to %s\n", port->name);
207 attached = 1;
208
209 calibrate_port(&device);
210
211 hrtimer_init(&device.timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
212 device.timer.function = hrtimer_event;
213 hrtimer_start(&device.timer, next_intr_time(&device), HRTIMER_MODE_ABS);
214
215 return;
216
217err_unregister_dev:
218 parport_unregister_device(device.pardev);
219}
220
221static void parport_detach(struct parport *port)
222{
223 if (port->cad != device.pardev)
224 return; /* not our port */
225
226 hrtimer_cancel(&device.timer);
227 parport_release(device.pardev);
228 parport_unregister_device(device.pardev);
229}
230
231static struct parport_driver pps_gen_parport_driver = {
232 .name = KBUILD_MODNAME,
233 .match_port = parport_attach,
234 .detach = parport_detach,
235 .devmodel = true,
236};
237module_parport_driver(pps_gen_parport_driver);
238
239MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
240MODULE_DESCRIPTION("parallel port PPS signal generator");
241MODULE_LICENSE("GPL");
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * pps_gen_parport.c -- kernel parallel port PPS signal generator
4 *
5 * Copyright (C) 2009 Alexander Gordeev <lasaine@lvk.cs.msu.su>
6 */
7
8
9/*
10 * TODO:
11 * fix issues when realtime clock is adjusted in a leap
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/time.h>
20#include <linux/hrtimer.h>
21#include <linux/parport.h>
22
23#define SIGNAL 0
24#define NO_SIGNAL PARPORT_CONTROL_STROBE
25
26/* module parameters */
27
28#define SEND_DELAY_MAX 100000
29
30static unsigned int send_delay = 30000;
31MODULE_PARM_DESC(delay,
32 "Delay between setting and dropping the signal (ns)");
33module_param_named(delay, send_delay, uint, 0);
34
35
36#define SAFETY_INTERVAL 3000 /* set the hrtimer earlier for safety (ns) */
37
38/* internal per port structure */
39struct pps_generator_pp {
40 struct pardevice *pardev; /* parport device */
41 struct hrtimer timer;
42 long port_write_time; /* calibrated port write time (ns) */
43};
44
45static struct pps_generator_pp device = {
46 .pardev = NULL,
47};
48
49static int attached;
50
51/* calibrated time between a hrtimer event and the reaction */
52static long hrtimer_error = SAFETY_INTERVAL;
53
54/* the kernel hrtimer event */
55static enum hrtimer_restart hrtimer_event(struct hrtimer *timer)
56{
57 struct timespec64 expire_time, ts1, ts2, ts3, dts;
58 struct pps_generator_pp *dev;
59 struct parport *port;
60 long lim, delta;
61 unsigned long flags;
62
63 /* We have to disable interrupts here. The idea is to prevent
64 * other interrupts on the same processor to introduce random
65 * lags while polling the clock. ktime_get_real_ts64() takes <1us on
66 * most machines while other interrupt handlers can take much
67 * more potentially.
68 *
69 * NB: approx time with blocked interrupts =
70 * send_delay + 3 * SAFETY_INTERVAL
71 */
72 local_irq_save(flags);
73
74 /* first of all we get the time stamp... */
75 ktime_get_real_ts64(&ts1);
76 expire_time = ktime_to_timespec64(hrtimer_get_softexpires(timer));
77 dev = container_of(timer, struct pps_generator_pp, timer);
78 lim = NSEC_PER_SEC - send_delay - dev->port_write_time;
79
80 /* check if we are late */
81 if (expire_time.tv_sec != ts1.tv_sec || ts1.tv_nsec > lim) {
82 local_irq_restore(flags);
83 pr_err("we are late this time %lld.%09ld\n",
84 (s64)ts1.tv_sec, ts1.tv_nsec);
85 goto done;
86 }
87
88 /* busy loop until the time is right for an assert edge */
89 do {
90 ktime_get_real_ts64(&ts2);
91 } while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
92
93 /* set the signal */
94 port = dev->pardev->port;
95 port->ops->write_control(port, SIGNAL);
96
97 /* busy loop until the time is right for a clear edge */
98 lim = NSEC_PER_SEC - dev->port_write_time;
99 do {
100 ktime_get_real_ts64(&ts2);
101 } while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
102
103 /* unset the signal */
104 port->ops->write_control(port, NO_SIGNAL);
105
106 ktime_get_real_ts64(&ts3);
107
108 local_irq_restore(flags);
109
110 /* update calibrated port write time */
111 dts = timespec64_sub(ts3, ts2);
112 dev->port_write_time =
113 (dev->port_write_time + timespec64_to_ns(&dts)) >> 1;
114
115done:
116 /* update calibrated hrtimer error */
117 dts = timespec64_sub(ts1, expire_time);
118 delta = timespec64_to_ns(&dts);
119 /* If the new error value is bigger then the old, use the new
120 * value, if not then slowly move towards the new value. This
121 * way it should be safe in bad conditions and efficient in
122 * good conditions.
123 */
124 if (delta >= hrtimer_error)
125 hrtimer_error = delta;
126 else
127 hrtimer_error = (3 * hrtimer_error + delta) >> 2;
128
129 /* update the hrtimer expire time */
130 hrtimer_set_expires(timer,
131 ktime_set(expire_time.tv_sec + 1,
132 NSEC_PER_SEC - (send_delay +
133 dev->port_write_time + SAFETY_INTERVAL +
134 2 * hrtimer_error)));
135
136 return HRTIMER_RESTART;
137}
138
139/* calibrate port write time */
140#define PORT_NTESTS_SHIFT 5
141static void calibrate_port(struct pps_generator_pp *dev)
142{
143 struct parport *port = dev->pardev->port;
144 int i;
145 long acc = 0;
146
147 for (i = 0; i < (1 << PORT_NTESTS_SHIFT); i++) {
148 struct timespec64 a, b;
149 unsigned long irq_flags;
150
151 local_irq_save(irq_flags);
152 ktime_get_real_ts64(&a);
153 port->ops->write_control(port, NO_SIGNAL);
154 ktime_get_real_ts64(&b);
155 local_irq_restore(irq_flags);
156
157 b = timespec64_sub(b, a);
158 acc += timespec64_to_ns(&b);
159 }
160
161 dev->port_write_time = acc >> PORT_NTESTS_SHIFT;
162 pr_info("port write takes %ldns\n", dev->port_write_time);
163}
164
165static inline ktime_t next_intr_time(struct pps_generator_pp *dev)
166{
167 struct timespec64 ts;
168
169 ktime_get_real_ts64(&ts);
170
171 return ktime_set(ts.tv_sec +
172 ((ts.tv_nsec > 990 * NSEC_PER_MSEC) ? 1 : 0),
173 NSEC_PER_SEC - (send_delay +
174 dev->port_write_time + 3 * SAFETY_INTERVAL));
175}
176
177static void parport_attach(struct parport *port)
178{
179 struct pardev_cb pps_cb;
180
181 if (send_delay > SEND_DELAY_MAX) {
182 pr_err("delay value should be not greater then %d\n", SEND_DELAY_MAX);
183 return;
184 }
185
186 if (attached) {
187 /* we already have a port */
188 return;
189 }
190
191 memset(&pps_cb, 0, sizeof(pps_cb));
192 pps_cb.private = &device;
193 pps_cb.flags = PARPORT_FLAG_EXCL;
194 device.pardev = parport_register_dev_model(port, KBUILD_MODNAME,
195 &pps_cb, 0);
196 if (!device.pardev) {
197 pr_err("couldn't register with %s\n", port->name);
198 return;
199 }
200
201 if (parport_claim_or_block(device.pardev) < 0) {
202 pr_err("couldn't claim %s\n", port->name);
203 goto err_unregister_dev;
204 }
205
206 pr_info("attached to %s\n", port->name);
207 attached = 1;
208
209 calibrate_port(&device);
210
211 hrtimer_init(&device.timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
212 device.timer.function = hrtimer_event;
213 hrtimer_start(&device.timer, next_intr_time(&device), HRTIMER_MODE_ABS);
214
215 return;
216
217err_unregister_dev:
218 parport_unregister_device(device.pardev);
219}
220
221static void parport_detach(struct parport *port)
222{
223 if (port->cad != device.pardev)
224 return; /* not our port */
225
226 hrtimer_cancel(&device.timer);
227 parport_release(device.pardev);
228 parport_unregister_device(device.pardev);
229}
230
231static struct parport_driver pps_gen_parport_driver = {
232 .name = KBUILD_MODNAME,
233 .match_port = parport_attach,
234 .detach = parport_detach,
235};
236module_parport_driver(pps_gen_parport_driver);
237
238MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
239MODULE_DESCRIPTION("parallel port PPS signal generator");
240MODULE_LICENSE("GPL");