/*
 * Copyright 2008  by Andreas Eversberg <andreas@eversberg.eu>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * 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.
 *
 * Quick API description:
 *
 * A clock source registers using mISDN_register_clock:
 *      name = text string to name clock source
 *      priority = value to priorize clock sources (0 = default)
 *      ctl = callback function to enable/disable clock source
 *      priv = private pointer of clock source
 *      return = pointer to clock source structure;
 *
 * Note: Callback 'ctl' can be called before mISDN_register_clock returns!
 *       Also it can be called during mISDN_unregister_clock.
 *
 * A clock source calls mISDN_clock_update with given samples elapsed, if
 * enabled. If function call is delayed, tv must be set with the timestamp
 * of the actual event.
 *
 * A clock source unregisters using mISDN_unregister_clock.
 *
 * To get current clock, call mISDN_clock_get. The signed short value
 * counts the number of samples since. Time since last clock event is added.
 *
 */

#include <linux/slab.h>
#include <linux/types.h>
#include <linux/stddef.h>
#include <linux/spinlock.h>
#include <linux/ktime.h>
#include <linux/mISDNif.h>
#include <linux/export.h>
#include "core.h"

static u_int *debug;
static LIST_HEAD(iclock_list);
static DEFINE_RWLOCK(iclock_lock);
static u16 iclock_count;                /* counter of last clock */
static ktime_t iclock_timestamp;        /* time stamp of last clock */
static int iclock_timestamp_valid;      /* already received one timestamp */
static struct mISDNclock *iclock_current;

void
mISDN_init_clock(u_int *dp)
{
        debug = dp;
        iclock_timestamp = ktime_get();
}

static void
select_iclock(void)
{
        struct mISDNclock *iclock, *bestclock = NULL, *lastclock = NULL;
        int pri = -128;

        list_for_each_entry(iclock, &iclock_list, list) {
                if (iclock->pri > pri) {
                        pri = iclock->pri;
                        bestclock = iclock;
                }
                if (iclock_current == iclock)
                        lastclock = iclock;
        }
        if (lastclock && bestclock != lastclock) {
                /* last used clock source still exists but changes, disable */
                if (*debug & DEBUG_CLOCK)
                        printk(KERN_DEBUG "Old clock source '%s' disable.\n",
                               lastclock->name);
                lastclock->ctl(lastclock->priv, 0);
        }
        if (bestclock && bestclock != iclock_current) {
                /* new clock source selected, enable */
                if (*debug & DEBUG_CLOCK)
                        printk(KERN_DEBUG "New clock source '%s' enable.\n",
                               bestclock->name);
                bestclock->ctl(bestclock->priv, 1);
        }
        if (bestclock != iclock_current) {
                /* no clock received yet */
                iclock_timestamp_valid = 0;
        }
        iclock_current = bestclock;
}

struct mISDNclock
*mISDN_register_clock(char *name, int pri, clockctl_func_t *ctl, void *priv)
{
        u_long                  flags;
        struct mISDNclock       *iclock;

        if (*debug & (DEBUG_CORE | DEBUG_CLOCK))
                printk(KERN_DEBUG "%s: %s %d\n", __func__, name, pri);
        iclock = kzalloc(sizeof(struct mISDNclock), GFP_ATOMIC);
        if (!iclock) {
                printk(KERN_ERR "%s: No memory for clock entry.\n", __func__);
                return NULL;
        }
        strncpy(iclock->name, name, sizeof(iclock->name) - 1);
        iclock->pri = pri;
        iclock->priv = priv;
        iclock->ctl = ctl;
        write_lock_irqsave(&iclock_lock, flags);
        list_add_tail(&iclock->list, &iclock_list);
        select_iclock();
        write_unlock_irqrestore(&iclock_lock, flags);
        return iclock;
}
EXPORT_SYMBOL(mISDN_register_clock);

void
mISDN_unregister_clock(struct mISDNclock *iclock)
{
        u_long  flags;

        if (*debug & (DEBUG_CORE | DEBUG_CLOCK))
                printk(KERN_DEBUG "%s: %s %d\n", __func__, iclock->name,
                       iclock->pri);
        write_lock_irqsave(&iclock_lock, flags);
        if (iclock_current == iclock) {
                if (*debug & DEBUG_CLOCK)
                        printk(KERN_DEBUG
                               "Current clock source '%s' unregisters.\n",
                               iclock->name);
                iclock->ctl(iclock->priv, 0);
        }
        list_del(&iclock->list);
        select_iclock();
        write_unlock_irqrestore(&iclock_lock, flags);
}
EXPORT_SYMBOL(mISDN_unregister_clock);

void
mISDN_clock_update(struct mISDNclock *iclock, int samples, ktime_t *timestamp)
{
        u_long          flags;
        ktime_t         timestamp_now;
        u16             delta;

        write_lock_irqsave(&iclock_lock, flags);
        if (iclock_current != iclock) {
                printk(KERN_ERR "%s: '%s' sends us clock updates, but we do "
                       "listen to '%s'. This is a bug!\n", __func__,
                       iclock->name,
                       iclock_current ? iclock_current->name : "nothing");
                iclock->ctl(iclock->priv, 0);
                write_unlock_irqrestore(&iclock_lock, flags);
                return;
        }
        if (iclock_timestamp_valid) {
                /* increment sample counter by given samples */
                iclock_count += samples;
                if (timestamp) { /* timestamp must be set, if function call is delayed */
                        iclock_timestamp = *timestamp;
                } else  {
                        iclock_timestamp = ktime_get();
                }
        } else {
                /* calc elapsed time by system clock */
                if (timestamp) { /* timestamp must be set, if function call is delayed */
                        timestamp_now = *timestamp;
                } else {
                        timestamp_now = ktime_get();
                }
                delta = ktime_divns(ktime_sub(timestamp_now, iclock_timestamp),
                                (NSEC_PER_SEC / 8000));
                /* add elapsed time to counter and set new timestamp */
                iclock_count += delta;
                iclock_timestamp = timestamp_now;
                iclock_timestamp_valid = 1;
                if (*debug & DEBUG_CLOCK)
                        printk("Received first clock from source '%s'.\n",
                               iclock_current ? iclock_current->name : "nothing");
        }
        write_unlock_irqrestore(&iclock_lock, flags);
}
EXPORT_SYMBOL(mISDN_clock_update);

unsigned short
mISDN_clock_get(void)
{
        u_long          flags;
        ktime_t         timestamp_now;
        u16             delta;
        u16             count;

        read_lock_irqsave(&iclock_lock, flags);
        /* calc elapsed time by system clock */
        timestamp_now = ktime_get();
        delta = ktime_divns(ktime_sub(timestamp_now, iclock_timestamp),
                        (NSEC_PER_SEC / 8000));
        /* add elapsed time to counter */
        count = iclock_count + delta;
        read_unlock_irqrestore(&iclock_lock, flags);
        return count;
}
EXPORT_SYMBOL(mISDN_clock_get);