/*
 *
 * Driver for ST M41T93 SPI RTC
 *
 * (c) 2010 Nikolaus Voss, Weinmann Medical GmbH
 *
 * 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.
 */

#include <linux/bcd.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/rtc.h>
#include <linux/spi/spi.h>

#define M41T93_REG_SSEC                 0
#define M41T93_REG_ST_SEC               1
#define M41T93_REG_MIN                  2
#define M41T93_REG_CENT_HOUR            3
#define M41T93_REG_WDAY                 4
#define M41T93_REG_DAY                  5
#define M41T93_REG_MON                  6
#define M41T93_REG_YEAR                 7


#define M41T93_REG_ALM_HOUR_HT          0xc
#define M41T93_REG_FLAGS                0xf

#define M41T93_FLAG_ST                  (1 << 7)
#define M41T93_FLAG_OF                  (1 << 2)
#define M41T93_FLAG_BL                  (1 << 4)
#define M41T93_FLAG_HT                  (1 << 6)

static inline int m41t93_set_reg(struct spi_device *spi, u8 addr, u8 data)
{
        u8 buf[2];

        /* MSB must be '1' to write */
        buf[0] = addr | 0x80;
        buf[1] = data;

        return spi_write(spi, buf, sizeof(buf));
}

static int m41t93_set_time(struct device *dev, struct rtc_time *tm)
{
        struct spi_device *spi = to_spi_device(dev);
        u8 buf[9] = {0x80};        /* write cmd + 8 data bytes */
        u8 * const data = &buf[1]; /* ptr to first data byte */

        dev_dbg(dev, "%s secs=%d, mins=%d, "
                "hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
                "write", tm->tm_sec, tm->tm_min,
                tm->tm_hour, tm->tm_mday,
                tm->tm_mon, tm->tm_year, tm->tm_wday);

        if (tm->tm_year < 100) {
                dev_warn(&spi->dev, "unsupported date (before 2000-01-01).\n");
                return -EINVAL;
        }

        data[M41T93_REG_SSEC]           = 0;
        data[M41T93_REG_ST_SEC]         = bin2bcd(tm->tm_sec);
        data[M41T93_REG_MIN]            = bin2bcd(tm->tm_min);
        data[M41T93_REG_CENT_HOUR]      = bin2bcd(tm->tm_hour) |
                                                ((tm->tm_year/100-1) << 6);
        data[M41T93_REG_DAY]            = bin2bcd(tm->tm_mday);
        data[M41T93_REG_WDAY]           = bin2bcd(tm->tm_wday + 1);
        data[M41T93_REG_MON]            = bin2bcd(tm->tm_mon + 1);
        data[M41T93_REG_YEAR]           = bin2bcd(tm->tm_year % 100);

        return spi_write(spi, buf, sizeof(buf));
}


static int m41t93_get_time(struct device *dev, struct rtc_time *tm)
{
        struct spi_device *spi = to_spi_device(dev);
        const u8 start_addr = 0;
        u8 buf[8];
        int century_after_1900;
        int tmp;
        int ret = 0;

        /* Check status of clock. Two states must be considered:
           1. halt bit (HT) is set: the clock is running but update of readout
              registers has been disabled due to power failure. This is normal
              case after poweron. Time is valid after resetting HT bit.
           2. oscillator fail bit (OF) is set. Oscillator has be stopped and
              time is invalid:
              a) OF can be immeditely reset.
              b) OF cannot be immediately reset: oscillator has to be restarted.
        */
        tmp = spi_w8r8(spi, M41T93_REG_ALM_HOUR_HT);
        if (tmp < 0)
                return tmp;

        if (tmp & M41T93_FLAG_HT) {
                dev_dbg(&spi->dev, "HT bit is set, reenable clock update.\n");
                m41t93_set_reg(spi, M41T93_REG_ALM_HOUR_HT,
                               tmp & ~M41T93_FLAG_HT);
        }

        tmp = spi_w8r8(spi, M41T93_REG_FLAGS);
        if (tmp < 0)
                return tmp;

        if (tmp & M41T93_FLAG_OF) {
                ret = -EINVAL;
                dev_warn(&spi->dev, "OF bit is set, resetting.\n");
                m41t93_set_reg(spi, M41T93_REG_FLAGS, tmp & ~M41T93_FLAG_OF);

                tmp = spi_w8r8(spi, M41T93_REG_FLAGS);
                if (tmp < 0)
                        return tmp;
                else if (tmp & M41T93_FLAG_OF) {
                        u8 reset_osc = buf[M41T93_REG_ST_SEC] | M41T93_FLAG_ST;

                        dev_warn(&spi->dev,
                                 "OF bit is still set, kickstarting clock.\n");
                        m41t93_set_reg(spi, M41T93_REG_ST_SEC, reset_osc);
                        reset_osc &= ~M41T93_FLAG_ST;
                        m41t93_set_reg(spi, M41T93_REG_ST_SEC, reset_osc);
                }
        }

        if (tmp & M41T93_FLAG_BL)
                dev_warn(&spi->dev, "BL bit is set, replace battery.\n");

        /* read actual time/date */
        tmp = spi_write_then_read(spi, &start_addr, 1, buf, sizeof(buf));
        if (tmp < 0)
                return tmp;

        tm->tm_sec      = bcd2bin(buf[M41T93_REG_ST_SEC]);
        tm->tm_min      = bcd2bin(buf[M41T93_REG_MIN]);
        tm->tm_hour     = bcd2bin(buf[M41T93_REG_CENT_HOUR] & 0x3f);
        tm->tm_mday     = bcd2bin(buf[M41T93_REG_DAY]);
        tm->tm_mon      = bcd2bin(buf[M41T93_REG_MON]) - 1;
        tm->tm_wday     = bcd2bin(buf[M41T93_REG_WDAY] & 0x0f) - 1;

        century_after_1900 = (buf[M41T93_REG_CENT_HOUR] >> 6) + 1;
        tm->tm_year = bcd2bin(buf[M41T93_REG_YEAR]) + century_after_1900 * 100;

        dev_dbg(dev, "%s secs=%d, mins=%d, "
                "hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
                "read", tm->tm_sec, tm->tm_min,
                tm->tm_hour, tm->tm_mday,
                tm->tm_mon, tm->tm_year, tm->tm_wday);

        return ret < 0 ? ret : rtc_valid_tm(tm);
}


static const struct rtc_class_ops m41t93_rtc_ops = {
        .read_time      = m41t93_get_time,
        .set_time       = m41t93_set_time,
};

static struct spi_driver m41t93_driver;

static int __devinit m41t93_probe(struct spi_device *spi)
{
        struct rtc_device *rtc;
        int res;

        spi->bits_per_word = 8;
        spi_setup(spi);

        res = spi_w8r8(spi, M41T93_REG_WDAY);
        if (res < 0 || (res & 0xf8) != 0) {
                dev_err(&spi->dev, "not found 0x%x.\n", res);
                return -ENODEV;
        }

        rtc = rtc_device_register(m41t93_driver.driver.name,
                &spi->dev, &m41t93_rtc_ops, THIS_MODULE);
        if (IS_ERR(rtc))
                return PTR_ERR(rtc);

        dev_set_drvdata(&spi->dev, rtc);

        return 0;
}


static int __devexit m41t93_remove(struct spi_device *spi)
{
        struct rtc_device *rtc = spi_get_drvdata(spi);

        if (rtc)
                rtc_device_unregister(rtc);

        return 0;
}

static struct spi_driver m41t93_driver = {
        .driver = {
                .name   = "rtc-m41t93",
                .owner  = THIS_MODULE,
        },
        .probe  = m41t93_probe,
        .remove = __devexit_p(m41t93_remove),
};

module_spi_driver(m41t93_driver);

MODULE_AUTHOR("Nikolaus Voss <n.voss@weinmann.de>");
MODULE_DESCRIPTION("Driver for ST M41T93 SPI RTC");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:rtc-m41t93");