/*
 * pps_parport.c -- kernel parallel port PPS client
 *
 *
 * 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:
 * 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 <lasaine@lvk.cs.msu.su>");
MODULE_DESCRIPTION(DRVDESC);
MODULE_LICENSE("GPL");