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 | |
30 | static unsigned int send_delay = 30000; |
31 | MODULE_PARM_DESC(delay, |
32 | "Delay between setting and dropping the signal (ns)" ); |
33 | module_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 */ |
39 | struct 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 | |
45 | static struct pps_generator_pp device = { |
46 | .pardev = NULL, |
47 | }; |
48 | |
49 | static int attached; |
50 | |
51 | /* calibrated time between a hrtimer event and the reaction */ |
52 | static long hrtimer_error = SAFETY_INTERVAL; |
53 | |
54 | /* the kernel hrtimer event */ |
55 | static 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(tv: &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(tv: &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(tv: &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(tv: &ts3); |
107 | |
108 | local_irq_restore(flags); |
109 | |
110 | /* update calibrated port write time */ |
111 | dts = timespec64_sub(lhs: ts3, rhs: ts2); |
112 | dev->port_write_time = |
113 | (dev->port_write_time + timespec64_to_ns(ts: &dts)) >> 1; |
114 | |
115 | done: |
116 | /* update calibrated hrtimer error */ |
117 | dts = timespec64_sub(lhs: ts1, rhs: expire_time); |
118 | delta = timespec64_to_ns(ts: &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 | time: ktime_set(secs: 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 |
141 | static 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(tv: &a); |
153 | port->ops->write_control(port, NO_SIGNAL); |
154 | ktime_get_real_ts64(tv: &b); |
155 | local_irq_restore(irq_flags); |
156 | |
157 | b = timespec64_sub(lhs: b, rhs: a); |
158 | acc += timespec64_to_ns(ts: &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 | |
165 | static inline ktime_t next_intr_time(struct pps_generator_pp *dev) |
166 | { |
167 | struct timespec64 ts; |
168 | |
169 | ktime_get_real_ts64(tv: &ts); |
170 | |
171 | return ktime_set(secs: 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 | |
177 | static 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 | par_dev_cb: &pps_cb, cnt: 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(dev: 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(dev: &device); |
210 | |
211 | hrtimer_init(timer: &device.timer, CLOCK_REALTIME, mode: HRTIMER_MODE_ABS); |
212 | device.timer.function = hrtimer_event; |
213 | hrtimer_start(timer: &device.timer, tim: next_intr_time(dev: &device), mode: HRTIMER_MODE_ABS); |
214 | |
215 | return; |
216 | |
217 | err_unregister_dev: |
218 | parport_unregister_device(dev: device.pardev); |
219 | } |
220 | |
221 | static void parport_detach(struct parport *port) |
222 | { |
223 | if (port->cad != device.pardev) |
224 | return; /* not our port */ |
225 | |
226 | hrtimer_cancel(timer: &device.timer); |
227 | parport_release(dev: device.pardev); |
228 | parport_unregister_device(dev: device.pardev); |
229 | } |
230 | |
231 | static struct parport_driver pps_gen_parport_driver = { |
232 | .name = KBUILD_MODNAME, |
233 | .match_port = parport_attach, |
234 | .detach = parport_detach, |
235 | .devmodel = true, |
236 | }; |
237 | module_parport_driver(pps_gen_parport_driver); |
238 | |
239 | MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>" ); |
240 | MODULE_DESCRIPTION("parallel port PPS signal generator" ); |
241 | MODULE_LICENSE("GPL" ); |
242 | |