pps: add parallel port PPS signal generator

Add 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.

[akpm@linux-foundation.org: fix build]
Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su>
Acked-by: Rodolfo Giometti <giometti@linux.it>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 301 insertions, 0 deletions

diff --git a/drivers/pps/generators/Kconfig b/drivers/pps/generators/Kconfig
new file mode 100644
index 000000000000..5fbd6148c804
--- /dev/null
+++ b/drivers/pps/generators/Kconfig
@@ -0,0 +1,17 @@
+#
+# PPS generators configuration
+#
+
+if PPS
+
+comment "PPS generators support"
+
+config PPS_GENERATOR_PARPORT
+        tristate "Parallel port PPS signal generator"
+        depends on PARPORT != n && GENERIC_TIME
+        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.
+
+endif
diff --git a/drivers/pps/generators/Makefile b/drivers/pps/generators/Makefile
new file mode 100644
index 000000000000..303304a6b8ec
--- /dev/null
+++ b/drivers/pps/generators/Makefile
@@ -0,0 +1,9 @@
+#
+# 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 000000000000..a15fe25efd55
--- /dev/null
+++ b/drivers/pps/generators/pps_gen_parport.c
@@ -0,0 +1,275 @@
+/*
+ * pps_gen_parport.c -- kernel parallel port PPS signal generator
+ *
+ *
+ * Copyright (C) 2009   Alexander Gordeev <lasaine@lvk.cs.msu.su>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+
+/*
+ * 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 DRVDESC "parallel port PPS signal generator"
+
+#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 timespec expire_time, ts1, ts2, ts3, dts;
+        struct pps_generator_pp *dev;
+        struct parport *port;
+        long lim, delta;
+        unsigned long flags;
+
+        /* NB: approx time with blocked interrupts =
+           send_delay + 3 * SAFETY_INTERVAL */
+        local_irq_save(flags);
+
+        /* first of all we get the time stamp... */
+        getnstimeofday(&ts1);
+        expire_time = ktime_to_timespec(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 %ld.%09ld\n",
+                                ts1.tv_sec, ts1.tv_nsec);
+                goto done;
+        }
+
+        /* busy loop until the time is right for an assert edge */
+        do {
+                getnstimeofday(&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 {
+                getnstimeofday(&ts2);
+        } while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
+
+        /* unset the signal */
+        port->ops->write_control(port, NO_SIGNAL);
+
+        getnstimeofday(&ts3);
+
+        local_irq_restore(flags);
+
+        /* update calibrated port write time */
+        dts = timespec_sub(ts3, ts2);
+        dev->port_write_time =
+                (dev->port_write_time + timespec_to_ns(&dts)) >> 1;
+
+done:
+        /* update calibrated hrtimer error */
+        dts = timespec_sub(ts1, expire_time);
+        delta = timespec_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 timespec a, b;
+                unsigned long irq_flags;
+
+                local_irq_save(irq_flags);
+                getnstimeofday(&a);
+                port->ops->write_control(port, NO_SIGNAL);
+                getnstimeofday(&b);
+                local_irq_restore(irq_flags);
+
+                b = timespec_sub(b, a);
+                acc += timespec_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 timespec ts;
+
+        getnstimeofday(&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)
+{
+        if (attached) {
+                /* we already have a port */
+                return;
+        }
+
+        device.pardev = parport_register_device(port, KBUILD_MODNAME,
+                        NULL, NULL, NULL, 0, &device);
+        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;
+#ifdef CONFIG_PREEMPT_RT
+        /* hrtimer interrupt will run in the interrupt context with this */
+        device.timer.irqsafe = 1;
+#endif
+
+        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,
+        .attach = parport_attach,
+        .detach = parport_detach,
+};
+
+/* module staff */
+
+static int __init pps_gen_parport_init(void)
+{
+        int ret;
+
+        pr_info(DRVDESC "\n");
+
+        if (send_delay > SEND_DELAY_MAX) {
+                pr_err("delay value should be not greater"
+                                " then %d\n", SEND_DELAY_MAX);
+                return -EINVAL;
+        }
+
+        ret = parport_register_driver(&pps_gen_parport_driver);
+        if (ret) {
+                pr_err("unable to register with parport\n");
+                return ret;
+        }
+
+        return  0;
+}
+
+static void __exit pps_gen_parport_exit(void)
+{
+        parport_unregister_driver(&pps_gen_parport_driver);
+        pr_info("hrtimer avg error is %ldns\n", hrtimer_error);
+}
+
+module_init(pps_gen_parport_init);
+module_exit(pps_gen_parport_exit);
+
+MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
+MODULE_DESCRIPTION(DRVDESC);
+MODULE_LICENSE("GPL");