// SPDX-License-Identifier: GPL-2.0-only
/* drivers/rtc/rtc-max6902.c
 *
 * Copyright (C) 2006 8D Technologies inc.
 * Copyright (C) 2004 Compulab Ltd.
 *
 * Driver for MAX6902 spi RTC
 */

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

#define MAX6902_REG_SECONDS             0x01
#define MAX6902_REG_MINUTES             0x03
#define MAX6902_REG_HOURS               0x05
#define MAX6902_REG_DATE                0x07
#define MAX6902_REG_MONTH               0x09
#define MAX6902_REG_DAY                 0x0B
#define MAX6902_REG_YEAR                0x0D
#define MAX6902_REG_CONTROL             0x0F
#define MAX6902_REG_CENTURY             0x13

static int max6902_set_reg(struct device *dev, unsigned char address,
                                unsigned char data)
{
        struct spi_device *spi = to_spi_device(dev);
        unsigned char buf[2];

        /* MSB must be '0' to write */
        buf[0] = address & 0x7f;
        buf[1] = data;

        return spi_write_then_read(spi, buf, 2, NULL, 0);
}

static int max6902_get_reg(struct device *dev, unsigned char address,
                                unsigned char *data)
{
        struct spi_device *spi = to_spi_device(dev);

        /* Set MSB to indicate read */
        *data = address | 0x80;

        return spi_write_then_read(spi, data, 1, data, 1);
}

static int max6902_read_time(struct device *dev, struct rtc_time *dt)
{
        int err, century;
        struct spi_device *spi = to_spi_device(dev);
        unsigned char buf[8];

        buf[0] = 0xbf;  /* Burst read */

        err = spi_write_then_read(spi, buf, 1, buf, 8);
        if (err != 0)
                return err;

        /* The chip sends data in this order:
         * Seconds, Minutes, Hours, Date, Month, Day, Year */
        dt->tm_sec      = bcd2bin(buf[0]);
        dt->tm_min      = bcd2bin(buf[1]);
        dt->tm_hour     = bcd2bin(buf[2]);
        dt->tm_mday     = bcd2bin(buf[3]);
        dt->tm_mon      = bcd2bin(buf[4]) - 1;
        dt->tm_wday     = bcd2bin(buf[5]);
        dt->tm_year     = bcd2bin(buf[6]);

        /* Read century */
        err = max6902_get_reg(dev, MAX6902_REG_CENTURY, &buf[0]);
        if (err != 0)
                return err;

        century = bcd2bin(buf[0]) * 100;

        dt->tm_year += century;
        dt->tm_year -= 1900;

        return 0;
}

static int max6902_set_time(struct device *dev, struct rtc_time *dt)
{
        dt->tm_year = dt->tm_year + 1900;

        /* Remove write protection */
        max6902_set_reg(dev, MAX6902_REG_CONTROL, 0);

        max6902_set_reg(dev, MAX6902_REG_SECONDS, bin2bcd(dt->tm_sec));
        max6902_set_reg(dev, MAX6902_REG_MINUTES, bin2bcd(dt->tm_min));
        max6902_set_reg(dev, MAX6902_REG_HOURS, bin2bcd(dt->tm_hour));

        max6902_set_reg(dev, MAX6902_REG_DATE, bin2bcd(dt->tm_mday));
        max6902_set_reg(dev, MAX6902_REG_MONTH, bin2bcd(dt->tm_mon + 1));
        max6902_set_reg(dev, MAX6902_REG_DAY, bin2bcd(dt->tm_wday));
        max6902_set_reg(dev, MAX6902_REG_YEAR, bin2bcd(dt->tm_year % 100));
        max6902_set_reg(dev, MAX6902_REG_CENTURY, bin2bcd(dt->tm_year / 100));

        /* Compulab used a delay here. However, the datasheet
         * does not mention a delay being required anywhere... */
        /* delay(2000); */

        /* Write protect */
        max6902_set_reg(dev, MAX6902_REG_CONTROL, 0x80);

        return 0;
}

static const struct rtc_class_ops max6902_rtc_ops = {
        .read_time      = max6902_read_time,
        .set_time       = max6902_set_time,
};

static int max6902_probe(struct spi_device *spi)
{
        struct rtc_device *rtc;
        unsigned char tmp;
        int res;

        spi->mode = SPI_MODE_3;
        spi->bits_per_word = 8;
        spi_setup(spi);

        res = max6902_get_reg(&spi->dev, MAX6902_REG_SECONDS, &tmp);
        if (res != 0)
                return res;

        rtc = devm_rtc_device_register(&spi->dev, "max6902",
                                &max6902_rtc_ops, THIS_MODULE);
        if (IS_ERR(rtc))
                return PTR_ERR(rtc);

        spi_set_drvdata(spi, rtc);
        return 0;
}

static struct spi_driver max6902_driver = {
        .driver = {
                .name   = "rtc-max6902",
        },
        .probe  = max6902_probe,
};

module_spi_driver(max6902_driver);

MODULE_DESCRIPTION("max6902 spi RTC driver");
MODULE_AUTHOR("Raphael Assenat");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:rtc-max6902");