diff options
Diffstat (limited to 'drivers/pps/generators/pps_gen_parport.c')
| -rw-r--r-- | drivers/pps/generators/pps_gen_parport.c | 241 |
1 files changed, 241 insertions, 0 deletions
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"); |