270 строки
6.6 KiB
C
270 строки
6.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* pps_gen_parport.c -- kernel parallel port PPS signal generator
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*
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* Copyright (C) 2009 Alexander Gordeev <lasaine@lvk.cs.msu.su>
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*/
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/*
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* TODO:
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* fix issues when realtime clock is adjusted in a leap
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/time.h>
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#include <linux/hrtimer.h>
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#include <linux/parport.h>
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#define DRVDESC "parallel port PPS signal generator"
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#define SIGNAL 0
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#define NO_SIGNAL PARPORT_CONTROL_STROBE
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/* module parameters */
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#define SEND_DELAY_MAX 100000
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static unsigned int send_delay = 30000;
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MODULE_PARM_DESC(delay,
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"Delay between setting and dropping the signal (ns)");
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module_param_named(delay, send_delay, uint, 0);
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#define SAFETY_INTERVAL 3000 /* set the hrtimer earlier for safety (ns) */
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/* internal per port structure */
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struct pps_generator_pp {
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struct pardevice *pardev; /* parport device */
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struct hrtimer timer;
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long port_write_time; /* calibrated port write time (ns) */
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};
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static struct pps_generator_pp device = {
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.pardev = NULL,
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};
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static int attached;
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/* calibrated time between a hrtimer event and the reaction */
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static long hrtimer_error = SAFETY_INTERVAL;
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/* the kernel hrtimer event */
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static enum hrtimer_restart hrtimer_event(struct hrtimer *timer)
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{
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struct timespec64 expire_time, ts1, ts2, ts3, dts;
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struct pps_generator_pp *dev;
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struct parport *port;
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long lim, delta;
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unsigned long flags;
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/* We have to disable interrupts here. The idea is to prevent
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* other interrupts on the same processor to introduce random
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* lags while polling the clock. ktime_get_real_ts64() takes <1us on
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* most machines while other interrupt handlers can take much
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* more potentially.
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*
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* NB: approx time with blocked interrupts =
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* send_delay + 3 * SAFETY_INTERVAL
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*/
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local_irq_save(flags);
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/* first of all we get the time stamp... */
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ktime_get_real_ts64(&ts1);
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expire_time = ktime_to_timespec64(hrtimer_get_softexpires(timer));
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dev = container_of(timer, struct pps_generator_pp, timer);
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lim = NSEC_PER_SEC - send_delay - dev->port_write_time;
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/* check if we are late */
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if (expire_time.tv_sec != ts1.tv_sec || ts1.tv_nsec > lim) {
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local_irq_restore(flags);
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pr_err("we are late this time %lld.%09ld\n",
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(s64)ts1.tv_sec, ts1.tv_nsec);
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goto done;
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}
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/* busy loop until the time is right for an assert edge */
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do {
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ktime_get_real_ts64(&ts2);
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} while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
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/* set the signal */
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port = dev->pardev->port;
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port->ops->write_control(port, SIGNAL);
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/* busy loop until the time is right for a clear edge */
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lim = NSEC_PER_SEC - dev->port_write_time;
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do {
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ktime_get_real_ts64(&ts2);
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} while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
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/* unset the signal */
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port->ops->write_control(port, NO_SIGNAL);
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ktime_get_real_ts64(&ts3);
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local_irq_restore(flags);
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/* update calibrated port write time */
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dts = timespec64_sub(ts3, ts2);
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dev->port_write_time =
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(dev->port_write_time + timespec64_to_ns(&dts)) >> 1;
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done:
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/* update calibrated hrtimer error */
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dts = timespec64_sub(ts1, expire_time);
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delta = timespec64_to_ns(&dts);
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/* If the new error value is bigger then the old, use the new
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* value, if not then slowly move towards the new value. This
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* way it should be safe in bad conditions and efficient in
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* good conditions.
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*/
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if (delta >= hrtimer_error)
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hrtimer_error = delta;
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else
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hrtimer_error = (3 * hrtimer_error + delta) >> 2;
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/* update the hrtimer expire time */
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hrtimer_set_expires(timer,
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ktime_set(expire_time.tv_sec + 1,
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NSEC_PER_SEC - (send_delay +
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dev->port_write_time + SAFETY_INTERVAL +
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2 * hrtimer_error)));
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return HRTIMER_RESTART;
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}
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/* calibrate port write time */
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#define PORT_NTESTS_SHIFT 5
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static void calibrate_port(struct pps_generator_pp *dev)
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{
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struct parport *port = dev->pardev->port;
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int i;
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long acc = 0;
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for (i = 0; i < (1 << PORT_NTESTS_SHIFT); i++) {
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struct timespec64 a, b;
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unsigned long irq_flags;
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local_irq_save(irq_flags);
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ktime_get_real_ts64(&a);
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port->ops->write_control(port, NO_SIGNAL);
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ktime_get_real_ts64(&b);
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local_irq_restore(irq_flags);
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b = timespec64_sub(b, a);
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acc += timespec64_to_ns(&b);
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}
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dev->port_write_time = acc >> PORT_NTESTS_SHIFT;
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pr_info("port write takes %ldns\n", dev->port_write_time);
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}
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static inline ktime_t next_intr_time(struct pps_generator_pp *dev)
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{
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struct timespec64 ts;
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ktime_get_real_ts64(&ts);
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return ktime_set(ts.tv_sec +
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((ts.tv_nsec > 990 * NSEC_PER_MSEC) ? 1 : 0),
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NSEC_PER_SEC - (send_delay +
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dev->port_write_time + 3 * SAFETY_INTERVAL));
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}
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static void parport_attach(struct parport *port)
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{
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struct pardev_cb pps_cb;
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if (attached) {
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/* we already have a port */
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return;
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}
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memset(&pps_cb, 0, sizeof(pps_cb));
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pps_cb.private = &device;
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pps_cb.flags = PARPORT_FLAG_EXCL;
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device.pardev = parport_register_dev_model(port, KBUILD_MODNAME,
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&pps_cb, 0);
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if (!device.pardev) {
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pr_err("couldn't register with %s\n", port->name);
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return;
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}
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if (parport_claim_or_block(device.pardev) < 0) {
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pr_err("couldn't claim %s\n", port->name);
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goto err_unregister_dev;
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}
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pr_info("attached to %s\n", port->name);
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attached = 1;
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calibrate_port(&device);
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hrtimer_init(&device.timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
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device.timer.function = hrtimer_event;
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hrtimer_start(&device.timer, next_intr_time(&device), HRTIMER_MODE_ABS);
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return;
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err_unregister_dev:
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parport_unregister_device(device.pardev);
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}
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static void parport_detach(struct parport *port)
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{
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if (port->cad != device.pardev)
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return; /* not our port */
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hrtimer_cancel(&device.timer);
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parport_release(device.pardev);
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parport_unregister_device(device.pardev);
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}
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static struct parport_driver pps_gen_parport_driver = {
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.name = KBUILD_MODNAME,
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.match_port = parport_attach,
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.detach = parport_detach,
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.devmodel = true,
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};
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/* module staff */
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static int __init pps_gen_parport_init(void)
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{
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int ret;
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pr_info(DRVDESC "\n");
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if (send_delay > SEND_DELAY_MAX) {
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pr_err("delay value should be not greater"
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" then %d\n", SEND_DELAY_MAX);
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return -EINVAL;
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}
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ret = parport_register_driver(&pps_gen_parport_driver);
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if (ret) {
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pr_err("unable to register with parport\n");
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return ret;
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}
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return 0;
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}
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static void __exit pps_gen_parport_exit(void)
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{
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parport_unregister_driver(&pps_gen_parport_driver);
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pr_info("hrtimer avg error is %ldns\n", hrtimer_error);
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}
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module_init(pps_gen_parport_init);
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module_exit(pps_gen_parport_exit);
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MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
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MODULE_DESCRIPTION(DRVDESC);
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MODULE_LICENSE("GPL");
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