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 DRVDESC "parallel port PPS signal generator"
24
25 #define SIGNAL 0
26 #define NO_SIGNAL PARPORT_CONTROL_STROBE
27
28 /* module parameters */
29
30 #define SEND_DELAY_MAX 100000
31
32 static unsigned int send_delay = 30000;
33 MODULE_PARM_DESC(delay,
34 "Delay between setting and dropping the signal (ns)");
35 module_param_named(delay, send_delay, uint, 0);
36
37
38 #define SAFETY_INTERVAL 3000 /* set the hrtimer earlier for safety (ns) */
39
40 /* internal per port structure */
41 struct pps_generator_pp {
42 struct pardevice *pardev; /* parport device */
43 struct hrtimer timer;
44 long port_write_time; /* calibrated port write time (ns) */
45 };
46
47 static struct pps_generator_pp device = {
48 .pardev = NULL,
49 };
50
51 static int attached;
52
53 /* calibrated time between a hrtimer event and the reaction */
54 static long hrtimer_error = SAFETY_INTERVAL;
55
56 /* the kernel hrtimer event */
hrtimer_event(struct hrtimer * timer)57 static enum hrtimer_restart hrtimer_event(struct hrtimer *timer)
58 {
59 struct timespec64 expire_time, ts1, ts2, ts3, dts;
60 struct pps_generator_pp *dev;
61 struct parport *port;
62 long lim, delta;
63 unsigned long flags;
64
65 /* We have to disable interrupts here. The idea is to prevent
66 * other interrupts on the same processor to introduce random
67 * lags while polling the clock. ktime_get_real_ts64() takes <1us on
68 * most machines while other interrupt handlers can take much
69 * more potentially.
70 *
71 * NB: approx time with blocked interrupts =
72 * send_delay + 3 * SAFETY_INTERVAL
73 */
74 local_irq_save(flags);
75
76 /* first of all we get the time stamp... */
77 ktime_get_real_ts64(&ts1);
78 expire_time = ktime_to_timespec64(hrtimer_get_softexpires(timer));
79 dev = container_of(timer, struct pps_generator_pp, timer);
80 lim = NSEC_PER_SEC - send_delay - dev->port_write_time;
81
82 /* check if we are late */
83 if (expire_time.tv_sec != ts1.tv_sec || ts1.tv_nsec > lim) {
84 local_irq_restore(flags);
85 pr_err("we are late this time %lld.%09ld\n",
86 (s64)ts1.tv_sec, ts1.tv_nsec);
87 goto done;
88 }
89
90 /* busy loop until the time is right for an assert edge */
91 do {
92 ktime_get_real_ts64(&ts2);
93 } while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
94
95 /* set the signal */
96 port = dev->pardev->port;
97 port->ops->write_control(port, SIGNAL);
98
99 /* busy loop until the time is right for a clear edge */
100 lim = NSEC_PER_SEC - dev->port_write_time;
101 do {
102 ktime_get_real_ts64(&ts2);
103 } while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
104
105 /* unset the signal */
106 port->ops->write_control(port, NO_SIGNAL);
107
108 ktime_get_real_ts64(&ts3);
109
110 local_irq_restore(flags);
111
112 /* update calibrated port write time */
113 dts = timespec64_sub(ts3, ts2);
114 dev->port_write_time =
115 (dev->port_write_time + timespec64_to_ns(&dts)) >> 1;
116
117 done:
118 /* update calibrated hrtimer error */
119 dts = timespec64_sub(ts1, expire_time);
120 delta = timespec64_to_ns(&dts);
121 /* If the new error value is bigger then the old, use the new
122 * value, if not then slowly move towards the new value. This
123 * way it should be safe in bad conditions and efficient in
124 * good conditions.
125 */
126 if (delta >= hrtimer_error)
127 hrtimer_error = delta;
128 else
129 hrtimer_error = (3 * hrtimer_error + delta) >> 2;
130
131 /* update the hrtimer expire time */
132 hrtimer_set_expires(timer,
133 ktime_set(expire_time.tv_sec + 1,
134 NSEC_PER_SEC - (send_delay +
135 dev->port_write_time + SAFETY_INTERVAL +
136 2 * hrtimer_error)));
137
138 return HRTIMER_RESTART;
139 }
140
141 /* calibrate port write time */
142 #define PORT_NTESTS_SHIFT 5
calibrate_port(struct pps_generator_pp * dev)143 static void calibrate_port(struct pps_generator_pp *dev)
144 {
145 struct parport *port = dev->pardev->port;
146 int i;
147 long acc = 0;
148
149 for (i = 0; i < (1 << PORT_NTESTS_SHIFT); i++) {
150 struct timespec64 a, b;
151 unsigned long irq_flags;
152
153 local_irq_save(irq_flags);
154 ktime_get_real_ts64(&a);
155 port->ops->write_control(port, NO_SIGNAL);
156 ktime_get_real_ts64(&b);
157 local_irq_restore(irq_flags);
158
159 b = timespec64_sub(b, a);
160 acc += timespec64_to_ns(&b);
161 }
162
163 dev->port_write_time = acc >> PORT_NTESTS_SHIFT;
164 pr_info("port write takes %ldns\n", dev->port_write_time);
165 }
166
next_intr_time(struct pps_generator_pp * dev)167 static inline ktime_t next_intr_time(struct pps_generator_pp *dev)
168 {
169 struct timespec64 ts;
170
171 ktime_get_real_ts64(&ts);
172
173 return ktime_set(ts.tv_sec +
174 ((ts.tv_nsec > 990 * NSEC_PER_MSEC) ? 1 : 0),
175 NSEC_PER_SEC - (send_delay +
176 dev->port_write_time + 3 * SAFETY_INTERVAL));
177 }
178
parport_attach(struct parport * port)179 static void parport_attach(struct parport *port)
180 {
181 struct pardev_cb pps_cb;
182
183 if (attached) {
184 /* we already have a port */
185 return;
186 }
187
188 memset(&pps_cb, 0, sizeof(pps_cb));
189 pps_cb.private = &device;
190 pps_cb.flags = PARPORT_FLAG_EXCL;
191 device.pardev = parport_register_dev_model(port, KBUILD_MODNAME,
192 &pps_cb, 0);
193 if (!device.pardev) {
194 pr_err("couldn't register with %s\n", port->name);
195 return;
196 }
197
198 if (parport_claim_or_block(device.pardev) < 0) {
199 pr_err("couldn't claim %s\n", port->name);
200 goto err_unregister_dev;
201 }
202
203 pr_info("attached to %s\n", port->name);
204 attached = 1;
205
206 calibrate_port(&device);
207
208 hrtimer_init(&device.timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
209 device.timer.function = hrtimer_event;
210 hrtimer_start(&device.timer, next_intr_time(&device), HRTIMER_MODE_ABS);
211
212 return;
213
214 err_unregister_dev:
215 parport_unregister_device(device.pardev);
216 }
217
parport_detach(struct parport * port)218 static void parport_detach(struct parport *port)
219 {
220 if (port->cad != device.pardev)
221 return; /* not our port */
222
223 hrtimer_cancel(&device.timer);
224 parport_release(device.pardev);
225 parport_unregister_device(device.pardev);
226 }
227
228 static struct parport_driver pps_gen_parport_driver = {
229 .name = KBUILD_MODNAME,
230 .match_port = parport_attach,
231 .detach = parport_detach,
232 .devmodel = true,
233 };
234
235 /* module staff */
236
pps_gen_parport_init(void)237 static int __init pps_gen_parport_init(void)
238 {
239 int ret;
240
241 pr_info(DRVDESC "\n");
242
243 if (send_delay > SEND_DELAY_MAX) {
244 pr_err("delay value should be not greater"
245 " then %d\n", SEND_DELAY_MAX);
246 return -EINVAL;
247 }
248
249 ret = parport_register_driver(&pps_gen_parport_driver);
250 if (ret) {
251 pr_err("unable to register with parport\n");
252 return ret;
253 }
254
255 return 0;
256 }
257
pps_gen_parport_exit(void)258 static void __exit pps_gen_parport_exit(void)
259 {
260 parport_unregister_driver(&pps_gen_parport_driver);
261 pr_info("hrtimer avg error is %ldns\n", hrtimer_error);
262 }
263
264 module_init(pps_gen_parport_init);
265 module_exit(pps_gen_parport_exit);
266
267 MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
268 MODULE_DESCRIPTION(DRVDESC);
269 MODULE_LICENSE("GPL");
270