// SPDX-License-Identifier: GPL-2.0-only
/* rtc-max6916.c
 *
 * Driver for MAXIM  max6916 Low Current, SPI Compatible
 * Real Time Clock
 *
 * Author : Venkat Prashanth B U <venkat.prashanth2498@gmail.com>
 */

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

/* Registers in max6916 rtc */

#define MAX6916_SECONDS_REG     0x01
#define MAX6916_MINUTES_REG     0x02
#define MAX6916_HOURS_REG       0x03
#define MAX6916_DATE_REG        0x04
#define MAX6916_MONTH_REG       0x05
#define MAX6916_DAY_REG 0x06
#define MAX6916_YEAR_REG        0x07
#define MAX6916_CONTROL_REG     0x08
#define MAX6916_STATUS_REG      0x0C
#define MAX6916_CLOCK_BURST     0x3F

static int max6916_read_reg(struct device *dev, unsigned char address,
                            unsigned char *data)
{
        struct spi_device *spi = to_spi_device(dev);

        *data = address | 0x80;

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

static int max6916_write_reg(struct device *dev, unsigned char address,
                             unsigned char data)
{
        struct spi_device *spi = to_spi_device(dev);
        unsigned char buf[2];

        buf[0] = address & 0x7F;
        buf[1] = data;

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

static int max6916_read_time(struct device *dev, struct rtc_time *dt)
{
        struct spi_device *spi = to_spi_device(dev);
        int err;
        unsigned char buf[8];

        buf[0] = MAX6916_CLOCK_BURST | 0x80;

        err = spi_write_then_read(spi, buf, 1, buf, 8);

        if (err)
                return err;

        dt->tm_sec = bcd2bin(buf[0]);
        dt->tm_min = bcd2bin(buf[1]);
        dt->tm_hour = bcd2bin(buf[2] & 0x3F);
        dt->tm_mday = bcd2bin(buf[3]);
        dt->tm_mon = bcd2bin(buf[4]) - 1;
        dt->tm_wday = bcd2bin(buf[5]) - 1;
        dt->tm_year = bcd2bin(buf[6]) + 100;

        return 0;
}

static int max6916_set_time(struct device *dev, struct rtc_time *dt)
{
        struct spi_device *spi = to_spi_device(dev);
        unsigned char buf[9];

        if (dt->tm_year < 100 || dt->tm_year > 199) {
                dev_err(&spi->dev, "Year must be between 2000 and 2099. It's %d.\n",
                        dt->tm_year + 1900);
                return -EINVAL;
        }

        buf[0] = MAX6916_CLOCK_BURST & 0x7F;
        buf[1] = bin2bcd(dt->tm_sec);
        buf[2] = bin2bcd(dt->tm_min);
        buf[3] = (bin2bcd(dt->tm_hour) & 0X3F);
        buf[4] = bin2bcd(dt->tm_mday);
        buf[5] = bin2bcd(dt->tm_mon + 1);
        buf[6] = bin2bcd(dt->tm_wday + 1);
        buf[7] = bin2bcd(dt->tm_year % 100);
        buf[8] = bin2bcd(0x00);

        /* write the rtc settings */
        return spi_write_then_read(spi, buf, 9, NULL, 0);
}

static const struct rtc_class_ops max6916_rtc_ops = {
        .read_time = max6916_read_time,
        .set_time = max6916_set_time,
};

static int max6916_probe(struct spi_device *spi)
{
        struct rtc_device *rtc;
        unsigned char data;
        int res;

        /* spi setup with max6916 in mode 3 and bits per word as 8 */
        spi->mode = SPI_MODE_3;
        spi->bits_per_word = 8;
        spi_setup(spi);

        /* RTC Settings */
        res = max6916_read_reg(&spi->dev, MAX6916_SECONDS_REG, &data);
        if (res)
                return res;

        /* Disable the write protect of rtc */
        max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data);
        data = data & ~(1 << 7);
        max6916_write_reg(&spi->dev, MAX6916_CONTROL_REG, data);

        /*Enable oscillator,disable oscillator stop flag, glitch filter*/
        max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data);
        data = data & 0x1B;
        max6916_write_reg(&spi->dev, MAX6916_STATUS_REG, data);

        /* display the settings */
        max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data);
        dev_info(&spi->dev, "MAX6916 RTC CTRL Reg = 0x%02x\n", data);

        max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data);
        dev_info(&spi->dev, "MAX6916 RTC Status Reg = 0x%02x\n", data);

        rtc = devm_rtc_device_register(&spi->dev, "max6916",
                                       &max6916_rtc_ops, THIS_MODULE);
        if (IS_ERR(rtc))
                return PTR_ERR(rtc);

        spi_set_drvdata(spi, rtc);

        return 0;
}

static struct spi_driver max6916_driver = {
        .driver = {
                .name = "max6916",
        },
        .probe = max6916_probe,
};
module_spi_driver(max6916_driver);

MODULE_DESCRIPTION("MAX6916 SPI RTC DRIVER");
MODULE_AUTHOR("Venkat Prashanth B U <venkat.prashanth2498@gmail.com>");
MODULE_LICENSE("GPL v2");