// SPDX-License-Identifier: GPL-2.0-only
/*
 * Driver for ST M41T94 SPI RTC
 *
 * Copyright (C) 2008 Kim B. Heino
 */

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

#define M41T94_REG_SECONDS      0x01
#define M41T94_REG_MINUTES      0x02
#define M41T94_REG_HOURS        0x03
#define M41T94_REG_WDAY         0x04
#define M41T94_REG_DAY          0x05
#define M41T94_REG_MONTH        0x06
#define M41T94_REG_YEAR         0x07
#define M41T94_REG_HT           0x0c

#define M41T94_BIT_HALT         0x40
#define M41T94_BIT_STOP         0x80
#define M41T94_BIT_CB           0x40
#define M41T94_BIT_CEB          0x80

static int m41t94_set_time(struct device *dev, struct rtc_time *tm)
{
        struct spi_device *spi = to_spi_device(dev);
        u8 buf[8]; /* write cmd + 7 registers */

        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);

        buf[0] = 0x80 | M41T94_REG_SECONDS; /* write time + date */
        buf[M41T94_REG_SECONDS] = bin2bcd(tm->tm_sec);
        buf[M41T94_REG_MINUTES] = bin2bcd(tm->tm_min);
        buf[M41T94_REG_HOURS]   = bin2bcd(tm->tm_hour);
        buf[M41T94_REG_WDAY]    = bin2bcd(tm->tm_wday + 1);
        buf[M41T94_REG_DAY]     = bin2bcd(tm->tm_mday);
        buf[M41T94_REG_MONTH]   = bin2bcd(tm->tm_mon + 1);

        buf[M41T94_REG_HOURS] |= M41T94_BIT_CEB;
        if (tm->tm_year >= 100)
                buf[M41T94_REG_HOURS] |= M41T94_BIT_CB;
        buf[M41T94_REG_YEAR] = bin2bcd(tm->tm_year % 100);

        return spi_write(spi, buf, 8);
}

static int m41t94_read_time(struct device *dev, struct rtc_time *tm)
{
        struct spi_device *spi = to_spi_device(dev);
        u8 buf[2];
        int ret, hour;

        /* clear halt update bit */
        ret = spi_w8r8(spi, M41T94_REG_HT);
        if (ret < 0)
                return ret;
        if (ret & M41T94_BIT_HALT) {
                buf[0] = 0x80 | M41T94_REG_HT;
                buf[1] = ret & ~M41T94_BIT_HALT;
                spi_write(spi, buf, 2);
        }

        /* clear stop bit */
        ret = spi_w8r8(spi, M41T94_REG_SECONDS);
        if (ret < 0)
                return ret;
        if (ret & M41T94_BIT_STOP) {
                buf[0] = 0x80 | M41T94_REG_SECONDS;
                buf[1] = ret & ~M41T94_BIT_STOP;
                spi_write(spi, buf, 2);
        }

        tm->tm_sec  = bcd2bin(spi_w8r8(spi, M41T94_REG_SECONDS));
        tm->tm_min  = bcd2bin(spi_w8r8(spi, M41T94_REG_MINUTES));
        hour = spi_w8r8(spi, M41T94_REG_HOURS);
        tm->tm_hour = bcd2bin(hour & 0x3f);
        tm->tm_wday = bcd2bin(spi_w8r8(spi, M41T94_REG_WDAY)) - 1;
        tm->tm_mday = bcd2bin(spi_w8r8(spi, M41T94_REG_DAY));
        tm->tm_mon  = bcd2bin(spi_w8r8(spi, M41T94_REG_MONTH)) - 1;
        tm->tm_year = bcd2bin(spi_w8r8(spi, M41T94_REG_YEAR));
        if ((hour & M41T94_BIT_CB) || !(hour & M41T94_BIT_CEB))
                tm->tm_year += 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 0;
}

static const struct rtc_class_ops m41t94_rtc_ops = {
        .read_time      = m41t94_read_time,
        .set_time       = m41t94_set_time,
};

static struct spi_driver m41t94_driver;

static int m41t94_probe(struct spi_device *spi)
{
        struct rtc_device *rtc;
        int res;

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

        res = spi_w8r8(spi, M41T94_REG_SECONDS);
        if (res < 0) {
                dev_err(&spi->dev, "not found.\n");
                return res;
        }

        rtc = devm_rtc_device_register(&spi->dev, m41t94_driver.driver.name,
                                        &m41t94_rtc_ops, THIS_MODULE);
        if (IS_ERR(rtc))
                return PTR_ERR(rtc);

        spi_set_drvdata(spi, rtc);

        return 0;
}

static struct spi_driver m41t94_driver = {
        .driver = {
                .name   = "rtc-m41t94",
        },
        .probe  = m41t94_probe,
};

module_spi_driver(m41t94_driver);

MODULE_AUTHOR("Kim B. Heino <Kim.Heino@bluegiga.com>");
MODULE_DESCRIPTION("Driver for ST M41T94 SPI RTC");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:rtc-m41t94");