pps_parport.c

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/*
 * pps_parport.c -- kernel parallel port PPS client
 *
 *
 * Copyright (C) 2009   Alexander Gordeev <[email protected]>
 *
 * 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:
 * implement echo over SEL pin
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/irqnr.h>
#include <linux/time.h>
#include <linux/parport.h>
#include <linux/pps_kernel.h>

#define DRVDESC "parallel port PPS client"

/* module parameters */

#define CLEAR_WAIT_MAX      100
#define CLEAR_WAIT_MAX_ERRORS   5

static unsigned int clear_wait = 100;
MODULE_PARM_DESC(clear_wait,
    "Maximum number of port reads when polling for signal clear,"
    " zero turns clear edge capture off entirely");
module_param(clear_wait, uint, 0);


/* internal per port structure */
struct pps_client_pp {
    struct pardevice *pardev;   /* parport device */
    struct pps_device *pps;     /* PPS device */
    unsigned int cw;        /* port clear timeout */
    unsigned int cw_err;        /* number of timeouts */
};

static inline int signal_is_set(struct parport *port)
{
    return (port->ops->read_status(port) & PARPORT_STATUS_ACK) != 0;
}

/* parport interrupt handler */
static void parport_irq(void *handle)
{
    struct pps_event_time ts_assert, ts_clear;
    struct pps_client_pp *dev = handle;
    struct parport *port = dev->pardev->port;
    unsigned int i;
    unsigned long flags;

    /* first of all we get the time stamp... */
    pps_get_ts(&ts_assert);

    if (dev->cw == 0)
        /* clear edge capture disabled */
        goto out_assert;

    /* try capture the clear edge */

    /* We have to disable interrupts here. The idea is to prevent
     * other interrupts on the same processor to introduce random
     * lags while polling the port. Reading from IO port is known
     * to take approximately 1us while other interrupt handlers can
     * take much more potentially.
     *
     * Interrupts won't be disabled for a long time because the
     * number of polls is limited by clear_wait parameter which is
     * kept rather low. So it should never be an issue.
     */
    local_irq_save(flags);
    /* check the signal (no signal means the pulse is lost this time) */
    if (!signal_is_set(port)) {
        local_irq_restore(flags);
        dev_err(dev->pps->dev, "lost the signal\n");
        goto out_assert;
    }

    /* poll the port until the signal is unset */
    for (i = dev->cw; i; i--)
        if (!signal_is_set(port)) {
            pps_get_ts(&ts_clear);
            local_irq_restore(flags);
            dev->cw_err = 0;
            goto out_both;
        }
    local_irq_restore(flags);

    /* timeout */
    dev->cw_err++;
    if (dev->cw_err >= CLEAR_WAIT_MAX_ERRORS) {
        dev_err(dev->pps->dev, "disabled clear edge capture after %d"
                " timeouts\n", dev->cw_err);
        dev->cw = 0;
        dev->cw_err = 0;
    }

out_assert:
    /* fire assert event */
    pps_event(dev->pps, &ts_assert,
            PPS_CAPTUREASSERT, NULL);
    return;

out_both:
    /* fire assert event */
    pps_event(dev->pps, &ts_assert,
            PPS_CAPTUREASSERT, NULL);
    /* fire clear event */
    pps_event(dev->pps, &ts_clear,
            PPS_CAPTURECLEAR, NULL);
    return;
}

static void parport_attach(struct parport *port)
{
    struct pps_client_pp *device;
    struct pps_source_info info = {
        .name       = KBUILD_MODNAME,
        .path       = "",
        .mode       = PPS_CAPTUREBOTH | \
                  PPS_OFFSETASSERT | PPS_OFFSETCLEAR | \
                  PPS_ECHOASSERT | PPS_ECHOCLEAR | \
                  PPS_CANWAIT | PPS_TSFMT_TSPEC,
        .owner      = THIS_MODULE,
        .dev        = NULL
    };

    device = kzalloc(sizeof(struct pps_client_pp), GFP_KERNEL);
    if (!device) {
        pr_err("memory allocation failed, not attaching\n");
        return;
    }

    device->pardev = parport_register_device(port, KBUILD_MODNAME,
            NULL, NULL, parport_irq, PARPORT_FLAG_EXCL, device);
    if (!device->pardev) {
        pr_err("couldn't register with %s\n", port->name);
        goto err_free;
    }

    if (parport_claim_or_block(device->pardev) < 0) {
        pr_err("couldn't claim %s\n", port->name);
        goto err_unregister_dev;
    }

    device->pps = pps_register_source(&info,
            PPS_CAPTUREBOTH | PPS_OFFSETASSERT | PPS_OFFSETCLEAR);
    if (device->pps == NULL) {
        pr_err("couldn't register PPS source\n");
        goto err_release_dev;
    }

    device->cw = clear_wait;

    port->ops->enable_irq(port);

    pr_info("attached to %s\n", port->name);

    return;

err_release_dev:
    parport_release(device->pardev);
err_unregister_dev:
    parport_unregister_device(device->pardev);
err_free:
    kfree(device);
}

static void parport_detach(struct parport *port)
{
    struct pardevice *pardev = port->cad;
    struct pps_client_pp *device;

    /* FIXME: oooh, this is ugly! */
    if (strcmp(pardev->name, KBUILD_MODNAME))
        /* not our port */
        return;

    device = pardev->private;

    port->ops->disable_irq(port);
    pps_unregister_source(device->pps);
    parport_release(pardev);
    parport_unregister_device(pardev);
    kfree(device);
}

static struct parport_driver pps_parport_driver = {
    .name = KBUILD_MODNAME,
    .attach = parport_attach,
    .detach = parport_detach,
};

/* module staff */

static int __init pps_parport_init(void)
{
    int ret;

    pr_info(DRVDESC "\n");

    if (clear_wait > CLEAR_WAIT_MAX) {
        pr_err("clear_wait value should be not greater"
                " then %d\n", CLEAR_WAIT_MAX);
        return -EINVAL;
    }

    ret = parport_register_driver(&pps_parport_driver);
    if (ret) {
        pr_err("unable to register with parport\n");
        return ret;
    }

    return  0;
}

static void __exit pps_parport_exit(void)
{
    parport_unregister_driver(&pps_parport_driver);
}

module_init(pps_parport_init);
module_exit(pps_parport_exit);

MODULE_AUTHOR("Alexander Gordeev <[email protected]>");
MODULE_DESCRIPTION(DRVDESC);
MODULE_LICENSE("GPL");