/*
 * RTC client/driver for the Maxim/Dallas DS1374 Real-Time Clock over I2C
 *
 * Based on code by Randy Vinson <rvinson@mvista.com>,
 * which was based on the m41t00.c by Mark Greer <mgreer@mvista.com>.
 *
 * Copyright (C) 2006-2007 Freescale Semiconductor
 *
 * 2005 (c) MontaVista Software, Inc. This file is licensed under
 * the terms of the GNU General Public License version 2. This program
 * is licensed "as is" without any warranty of any kind, whether express
 * or implied.
 */
/*
 * It would be more efficient to use i2c msgs/i2c_transfer directly but, as
 * recommened in .../Documentation/i2c/writing-clients section
 * "Sending and receiving", using SMBus level communication is preferred.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/i2c.h>
#include <linux/rtc.h>
#include <linux/bcd.h>
#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/pm.h>

#define DS1374_REG_TOD0         0x00 /* Time of Day */
#define DS1374_REG_TOD1         0x01
#define DS1374_REG_TOD2         0x02
#define DS1374_REG_TOD3         0x03
#define DS1374_REG_WDALM0       0x04 /* Watchdog/Alarm */
#define DS1374_REG_WDALM1       0x05
#define DS1374_REG_WDALM2       0x06
#define DS1374_REG_CR           0x07 /* Control */
#define DS1374_REG_CR_AIE       0x01 /* Alarm Int. Enable */
#define DS1374_REG_CR_WDALM     0x20 /* 1=Watchdog, 0=Alarm */
#define DS1374_REG_CR_WACE      0x40 /* WD/Alarm counter enable */
#define DS1374_REG_SR           0x08 /* Status */
#define DS1374_REG_SR_OSF       0x80 /* Oscillator Stop Flag */
#define DS1374_REG_SR_AF        0x01 /* Alarm Flag */
#define DS1374_REG_TCR          0x09 /* Trickle Charge */

static const struct i2c_device_id ds1374_id[] = {
        { "ds1374", 0 },
        { }
};
MODULE_DEVICE_TABLE(i2c, ds1374_id);

struct ds1374 {
        struct i2c_client *client;
        struct rtc_device *rtc;
        struct work_struct work;

        /* The mutex protects alarm operations, and prevents a race
         * between the enable_irq() in the workqueue and the free_irq()
         * in the remove function.
         */
        struct mutex mutex;
        int exiting;
};

static struct i2c_driver ds1374_driver;

static int ds1374_read_rtc(struct i2c_client *client, u32 *time,
                           int reg, int nbytes)
{
        u8 buf[4];
        int ret;
        int i;

        if (nbytes > 4) {
                WARN_ON(1);
                return -EINVAL;
        }

        ret = i2c_smbus_read_i2c_block_data(client, reg, nbytes, buf);

        if (ret < 0)
                return ret;
        if (ret < nbytes)
                return -EIO;

        for (i = nbytes - 1, *time = 0; i >= 0; i--)
                *time = (*time << 8) | buf[i];

        return 0;
}

static int ds1374_write_rtc(struct i2c_client *client, u32 time,
                            int reg, int nbytes)
{
        u8 buf[4];
        int i;

        if (nbytes > 4) {
                WARN_ON(1);
                return -EINVAL;
        }

        for (i = 0; i < nbytes; i++) {
                buf[i] = time & 0xff;
                time >>= 8;
        }

        return i2c_smbus_write_i2c_block_data(client, reg, nbytes, buf);
}

static int ds1374_check_rtc_status(struct i2c_client *client)
{
        int ret = 0;
        int control, stat;

        stat = i2c_smbus_read_byte_data(client, DS1374_REG_SR);
        if (stat < 0)
                return stat;

        if (stat & DS1374_REG_SR_OSF)
                dev_warn(&client->dev,
                         "oscillator discontinuity flagged, time unreliable\n");

        stat &= ~(DS1374_REG_SR_OSF | DS1374_REG_SR_AF);

        ret = i2c_smbus_write_byte_data(client, DS1374_REG_SR, stat);
        if (ret < 0)
                return ret;

        /* If the alarm is pending, clear it before requesting
         * the interrupt, so an interrupt event isn't reported
         * before everything is initialized.
         */

        control = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
        if (control < 0)
                return control;

        control &= ~(DS1374_REG_CR_WACE | DS1374_REG_CR_AIE);
        return i2c_smbus_write_byte_data(client, DS1374_REG_CR, control);
}

static int ds1374_read_time(struct device *dev, struct rtc_time *time)
{
        struct i2c_client *client = to_i2c_client(dev);
        u32 itime;
        int ret;

        ret = ds1374_read_rtc(client, &itime, DS1374_REG_TOD0, 4);
        if (!ret)
                rtc_time_to_tm(itime, time);

        return ret;
}

static int ds1374_set_time(struct device *dev, struct rtc_time *time)
{
        struct i2c_client *client = to_i2c_client(dev);
        unsigned long itime;

        rtc_tm_to_time(time, &itime);
        return ds1374_write_rtc(client, itime, DS1374_REG_TOD0, 4);
}

/* The ds1374 has a decrementer for an alarm, rather than a comparator.
 * If the time of day is changed, then the alarm will need to be
 * reset.
 */
static int ds1374_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
{
        struct i2c_client *client = to_i2c_client(dev);
        struct ds1374 *ds1374 = i2c_get_clientdata(client);
        u32 now, cur_alarm;
        int cr, sr;
        int ret = 0;

        if (client->irq <= 0)
                return -EINVAL;

        mutex_lock(&ds1374->mutex);

        cr = ret = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
        if (ret < 0)
                goto out;

        sr = ret = i2c_smbus_read_byte_data(client, DS1374_REG_SR);
        if (ret < 0)
                goto out;

        ret = ds1374_read_rtc(client, &now, DS1374_REG_TOD0, 4);
        if (ret)
                goto out;

        ret = ds1374_read_rtc(client, &cur_alarm, DS1374_REG_WDALM0, 3);
        if (ret)
                goto out;

        rtc_time_to_tm(now + cur_alarm, &alarm->time);
        alarm->enabled = !!(cr & DS1374_REG_CR_WACE);
        alarm->pending = !!(sr & DS1374_REG_SR_AF);

out:
        mutex_unlock(&ds1374->mutex);
        return ret;
}

static int ds1374_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
{
        struct i2c_client *client = to_i2c_client(dev);
        struct ds1374 *ds1374 = i2c_get_clientdata(client);
        struct rtc_time now;
        unsigned long new_alarm, itime;
        int cr;
        int ret = 0;

        if (client->irq <= 0)
                return -EINVAL;

        ret = ds1374_read_time(dev, &now);
        if (ret < 0)
                return ret;

        rtc_tm_to_time(&alarm->time, &new_alarm);
        rtc_tm_to_time(&now, &itime);

        /* This can happen due to races, in addition to dates that are
         * truly in the past.  To avoid requiring the caller to check for
         * races, dates in the past are assumed to be in the recent past
         * (i.e. not something that we'd rather the caller know about via
         * an error), and the alarm is set to go off as soon as possible.
         */
        if (time_before_eq(new_alarm, itime))
                new_alarm = 1;
        else
                new_alarm -= itime;

        mutex_lock(&ds1374->mutex);

        ret = cr = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
        if (ret < 0)
                goto out;

        /* Disable any existing alarm before setting the new one
         * (or lack thereof). */
        cr &= ~DS1374_REG_CR_WACE;

        ret = i2c_smbus_write_byte_data(client, DS1374_REG_CR, cr);
        if (ret < 0)
                goto out;

        ret = ds1374_write_rtc(client, new_alarm, DS1374_REG_WDALM0, 3);
        if (ret)
                goto out;

        if (alarm->enabled) {
                cr |= DS1374_REG_CR_WACE | DS1374_REG_CR_AIE;
                cr &= ~DS1374_REG_CR_WDALM;

                ret = i2c_smbus_write_byte_data(client, DS1374_REG_CR, cr);
        }

out:
        mutex_unlock(&ds1374->mutex);
        return ret;
}

static irqreturn_t ds1374_irq(int irq, void *dev_id)
{
        struct i2c_client *client = dev_id;
        struct ds1374 *ds1374 = i2c_get_clientdata(client);

        disable_irq_nosync(irq);
        schedule_work(&ds1374->work);
        return IRQ_HANDLED;
}

static void ds1374_work(struct work_struct *work)
{
        struct ds1374 *ds1374 = container_of(work, struct ds1374, work);
        struct i2c_client *client = ds1374->client;
        int stat, control;

        mutex_lock(&ds1374->mutex);

        stat = i2c_smbus_read_byte_data(client, DS1374_REG_SR);
        if (stat < 0)
                goto unlock;

        if (stat & DS1374_REG_SR_AF) {
                stat &= ~DS1374_REG_SR_AF;
                i2c_smbus_write_byte_data(client, DS1374_REG_SR, stat);

                control = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
                if (control < 0)
                        goto out;

                control &= ~(DS1374_REG_CR_WACE | DS1374_REG_CR_AIE);
                i2c_smbus_write_byte_data(client, DS1374_REG_CR, control);

                rtc_update_irq(ds1374->rtc, 1, RTC_AF | RTC_IRQF);
        }

out:
        if (!ds1374->exiting)
                enable_irq(client->irq);
unlock:
        mutex_unlock(&ds1374->mutex);
}

static int ds1374_alarm_irq_enable(struct device *dev, unsigned int enabled)
{
        struct i2c_client *client = to_i2c_client(dev);
        struct ds1374 *ds1374 = i2c_get_clientdata(client);
        int ret;

        mutex_lock(&ds1374->mutex);

        ret = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
        if (ret < 0)
                goto out;

        if (enabled) {
                ret |= DS1374_REG_CR_WACE | DS1374_REG_CR_AIE;
                ret &= ~DS1374_REG_CR_WDALM;
        } else {
                ret &= ~DS1374_REG_CR_WACE;
        }
        ret = i2c_smbus_write_byte_data(client, DS1374_REG_CR, ret);

out:
        mutex_unlock(&ds1374->mutex);
        return ret;
}

static const struct rtc_class_ops ds1374_rtc_ops = {
        .read_time = ds1374_read_time,
        .set_time = ds1374_set_time,
        .read_alarm = ds1374_read_alarm,
        .set_alarm = ds1374_set_alarm,
        .alarm_irq_enable = ds1374_alarm_irq_enable,
};

static int ds1374_probe(struct i2c_client *client,
                        const struct i2c_device_id *id)
{
        struct ds1374 *ds1374;
        int ret;

        ds1374 = devm_kzalloc(&client->dev, sizeof(struct ds1374), GFP_KERNEL);
        if (!ds1374)
                return -ENOMEM;

        ds1374->client = client;
        i2c_set_clientdata(client, ds1374);

        INIT_WORK(&ds1374->work, ds1374_work);
        mutex_init(&ds1374->mutex);

        ret = ds1374_check_rtc_status(client);
        if (ret)
                return ret;

        if (client->irq > 0) {
                ret = devm_request_irq(&client->dev, client->irq, ds1374_irq, 0,
                                        "ds1374", client);
                if (ret) {
                        dev_err(&client->dev, "unable to request IRQ\n");
                        return ret;
                }

                device_set_wakeup_capable(&client->dev, 1);
        }

        ds1374->rtc = devm_rtc_device_register(&client->dev, client->name,
                                                &ds1374_rtc_ops, THIS_MODULE);
        if (IS_ERR(ds1374->rtc)) {
                dev_err(&client->dev, "unable to register the class device\n");
                return PTR_ERR(ds1374->rtc);
        }

        return 0;
}

static int ds1374_remove(struct i2c_client *client)
{
        struct ds1374 *ds1374 = i2c_get_clientdata(client);

        if (client->irq > 0) {
                mutex_lock(&ds1374->mutex);
                ds1374->exiting = 1;
                mutex_unlock(&ds1374->mutex);

                devm_free_irq(&client->dev, client->irq, client);
                cancel_work_sync(&ds1374->work);
        }

        return 0;
}

#ifdef CONFIG_PM_SLEEP
static int ds1374_suspend(struct device *dev)
{
        struct i2c_client *client = to_i2c_client(dev);

        if (client->irq >= 0 && device_may_wakeup(&client->dev))
                enable_irq_wake(client->irq);
        return 0;
}

static int ds1374_resume(struct device *dev)
{
        struct i2c_client *client = to_i2c_client(dev);

        if (client->irq >= 0 && device_may_wakeup(&client->dev))
                disable_irq_wake(client->irq);
        return 0;
}
#endif

static SIMPLE_DEV_PM_OPS(ds1374_pm, ds1374_suspend, ds1374_resume);

static struct i2c_driver ds1374_driver = {
        .driver = {
                .name = "rtc-ds1374",
                .owner = THIS_MODULE,
                .pm = &ds1374_pm,
        },
        .probe = ds1374_probe,
        .remove = ds1374_remove,
        .id_table = ds1374_id,
};

module_i2c_driver(ds1374_driver);

MODULE_AUTHOR("Scott Wood <scottwood@freescale.com>");
MODULE_DESCRIPTION("Maxim/Dallas DS1374 RTC Driver");
MODULE_LICENSE("GPL");