[linux-block.git] / drivers / pps / generators / pps_gen_parport.c

// 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,
};
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");
Commit	Line	Data
74ba9207	1	// SPDX-License-Identifier: GPL-2.0-or-later
46b402a0 AG	2	/*
	3	* pps_gen_parport.c -- kernel parallel port PPS signal generator
	4	*
46b402a0	5	* Copyright (C) 2009 Alexander Gordeev <lasaine@lvk.cs.msu.su>
46b402a0 AG	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
46b402a0 AG	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	{
28f3a488	57	struct timespec64 expire_time, ts1, ts2, ts3, dts;
46b402a0 AG	58	struct pps_generator_pp *dev;
	59	struct parport *port;
	60	long lim, delta;
	61	unsigned long flags;
	62
563558b2 AG	63	/* We have to disable interrupts here. The idea is to prevent
563558b2 AG	64	* other interrupts on the same processor to introduce random
28f3a488	65	* lags while polling the clock. ktime_get_real_ts64() takes <1us on
563558b2 AG	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	*/
46b402a0 AG	72	local_irq_save(flags);
	73
	74	/* first of all we get the time stamp... */
28f3a488 AB	75	ktime_get_real_ts64(&ts1);
28f3a488 AB	76	expire_time = ktime_to_timespec64(hrtimer_get_softexpires(timer));
46b402a0 AG	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);
28f3a488 AB	83	pr_err("we are late this time %lld.%09ld\n",
28f3a488 AB	84	(s64)ts1.tv_sec, ts1.tv_nsec);
46b402a0 AG	85	goto done;
	86	}
	87
	88	/* busy loop until the time is right for an assert edge */
	89	do {
28f3a488	90	ktime_get_real_ts64(&ts2);
46b402a0 AG	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 {
28f3a488	100	ktime_get_real_ts64(&ts2);
46b402a0 AG	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
28f3a488	106	ktime_get_real_ts64(&ts3);
46b402a0 AG	107
	108	local_irq_restore(flags);
	109
	110	/* update calibrated port write time */
28f3a488	111	dts = timespec64_sub(ts3, ts2);
46b402a0	112	dev->port_write_time =
28f3a488	113	(dev->port_write_time + timespec64_to_ns(&dts)) >> 1;
46b402a0 AG	114
	115	done:
	116	/* update calibrated hrtimer error */
28f3a488 AB	117	dts = timespec64_sub(ts1, expire_time);
28f3a488 AB	118	delta = timespec64_to_ns(&dts);
46b402a0 AG	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
	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++) {
28f3a488	148	struct timespec64 a, b;
46b402a0 AG	149	unsigned long irq_flags;
	150
	151	local_irq_save(irq_flags);
28f3a488	152	ktime_get_real_ts64(&a);
46b402a0	153	port->ops->write_control(port, NO_SIGNAL);
28f3a488	154	ktime_get_real_ts64(&b);
46b402a0 AG	155	local_irq_restore(irq_flags);
46b402a0 AG	156
28f3a488 AB	157	b = timespec64_sub(b, a);
28f3a488 AB	158	acc += timespec64_to_ns(&b);
46b402a0 AG	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	{
28f3a488	167	struct timespec64 ts;
46b402a0	168
28f3a488	169	ktime_get_real_ts64(&ts);
46b402a0 AG	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
	177	static void parport_attach(struct parport *port)
	178	{
b857cacd SM	179	struct pardev_cb pps_cb;
b857cacd SM	180
e0de88dc AS	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
46b402a0 AG	186	if (attached) {
	187	/* we already have a port */
	188	return;
	189	}
	190
b857cacd SM	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);
46b402a0 AG	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;
46b402a0 AG	213	hrtimer_start(&device.timer, next_intr_time(&device), HRTIMER_MODE_ABS);
	214
	215	return;
	216
	217	err_unregister_dev:
	218	parport_unregister_device(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(&device.timer);
	227	parport_release(device.pardev);
	228	parport_unregister_device(device.pardev);
	229	}
	230
	231	static struct parport_driver pps_gen_parport_driver = {
	232	.name = KBUILD_MODNAME,
b857cacd	233	.match_port = parport_attach,
46b402a0 AG	234	.detach = parport_detach,
46b402a0 AG	235	};
e0de88dc	236	module_parport_driver(pps_gen_parport_driver);
46b402a0 AG	237
46b402a0 AG	238	MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
e0de88dc	239	MODULE_DESCRIPTION("parallel port PPS signal generator");
46b402a0	240	MODULE_LICENSE("GPL");