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Message-ID: <fa113af6-95a1-4bc9-9234-79d0d8d7e650@enneenne.com>
Date: Fri, 19 Dec 2025 14:49:00 +0100
From: Rodolfo Giometti <giometti@...eenne.com>
To: Ethan Nelson-Moore <enelsonmoore@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pps: generators: remove broken pps_gen_parport driver
On 19/12/25 04:16, Ethan Nelson-Moore wrote:
> This driver was introduced in January 2011 and has been marked
> BROKEN for almost its entire existence (since commit
> 95b90afec301f050f72740e8696f7cce8a37db5a in March 2011).
> It is unlikely anyone will fix the driver at this point.
>
> Signed-off-by: Ethan Nelson-Moore <enelsonmoore@...il.com>
Acked-by: Rodolfo Giometti <giometti@...eenne.com>
> ---
> drivers/pps/generators/Kconfig | 8 -
> drivers/pps/generators/Makefile | 1 -
> drivers/pps/generators/pps_gen_parport.c | 238 -----------------------
> 3 files changed, 247 deletions(-)
> delete mode 100644 drivers/pps/generators/pps_gen_parport.c
>
> diff --git a/drivers/pps/generators/Kconfig b/drivers/pps/generators/Kconfig
> index b3f340ed3163..4ef02b3f2576 100644
> --- a/drivers/pps/generators/Kconfig
> +++ b/drivers/pps/generators/Kconfig
> @@ -23,14 +23,6 @@ config PPS_GENERATOR_DUMMY
> This driver can also be built as a module. If so, the module
> will be called pps_gen-dummy.
>
> -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.
> -
> config PPS_GENERATOR_TIO
> tristate "TIO PPS signal generator"
> depends on X86 && CPU_SUP_INTEL
> diff --git a/drivers/pps/generators/Makefile b/drivers/pps/generators/Makefile
> index e109920e8a2d..5d38774b4a56 100644
> --- a/drivers/pps/generators/Makefile
> +++ b/drivers/pps/generators/Makefile
> @@ -7,7 +7,6 @@ pps_gen_core-y := pps_gen.o sysfs.o
> obj-$(CONFIG_PPS_GENERATOR) := pps_gen_core.o
>
> obj-$(CONFIG_PPS_GENERATOR_DUMMY) += pps_gen-dummy.o
> -obj-$(CONFIG_PPS_GENERATOR_PARPORT) += pps_gen_parport.o
> obj-$(CONFIG_PPS_GENERATOR_TIO) += pps_gen_tio.o
>
> ccflags-$(CONFIG_PPS_DEBUG) := -DDEBUG
> diff --git a/drivers/pps/generators/pps_gen_parport.c b/drivers/pps/generators/pps_gen_parport.c
> deleted file mode 100644
> index 05bbf8d30ef1..000000000000
> --- a/drivers/pps/generators/pps_gen_parport.c
> +++ /dev/null
> @@ -1,238 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0-or-later
> -/*
> - * pps_gen_parport.c -- kernel parallel port PPS signal generator
> - *
> - * Copyright (C) 2009 Alexander Gordeev <lasaine@....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 %ptSp\n", &ts1);
> - 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_setup(&device.timer, hrtimer_event, CLOCK_REALTIME, HRTIMER_MODE_ABS);
> - 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@....cs.msu.su>");
> -MODULE_DESCRIPTION("parallel port PPS signal generator");
> -MODULE_LICENSE("GPL");
--
GNU/Linux Solutions e-mail: giometti@...eenne.com
Linux Device Driver giometti@...ux.it
Embedded Systems phone: +39 349 2432127
UNIX programming
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