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