3 files changed, 265 insertions, 0 deletions

diff --git a/drivers/pps/generators/Kconfig b/drivers/pps/generators/Kconfig
new file mode 100644
index 000000000..d615e640f
--- /dev/null
+++ b/drivers/pps/generators/Kconfig
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# PPS generators configuration
+#
+
+comment "PPS generators support"
+
+config PPS_GENERATOR_PARPORT
+	tristate "Parallel port PPS signal generator"
+	depends on PARPORT && BROKEN
+	help
+	  If you say yes here you get support for a PPS signal generator which
+	  utilizes STROBE pin of a parallel port to send PPS signals. It uses
+	  parport abstraction layer and hrtimers to precisely control the signal.
diff --git a/drivers/pps/generators/Makefile b/drivers/pps/generators/Makefile
new file mode 100644
index 000000000..2d56dd049
--- /dev/null
+++ b/drivers/pps/generators/Makefile
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Makefile for PPS generators.
+#
+
+obj-$(CONFIG_PPS_GENERATOR_PARPORT) += pps_gen_parport.o
+
+ifeq ($(CONFIG_PPS_DEBUG),y)
+EXTRA_CFLAGS += -DDEBUG
+endif
diff --git a/drivers/pps/generators/pps_gen_parport.c b/drivers/pps/generators/pps_gen_parport.c
new file mode 100644
index 000000000..b3e084b75
--- /dev/null
+++ b/drivers/pps/generators/pps_gen_parport.c
@@ -0,0 +1,241 @@
+// 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");