// SPDX-License-Identifier: GPL-2.0
/*
 * Real Time Clock (RTC) Driver for sd3078
 * Copyright (C) 2018 Zoro Li
 */

#include <linux/bcd.h>
#include <linux/i2c.h>
#include <linux/module.h>
#include <linux/regmap.h>
#include <linux/rtc.h>
#include <linux/slab.h>

#define SD3078_REG_SC                   0x00
#define SD3078_REG_MN                   0x01
#define SD3078_REG_HR                   0x02
#define SD3078_REG_DW                   0x03
#define SD3078_REG_DM                   0x04
#define SD3078_REG_MO                   0x05
#define SD3078_REG_YR                   0x06

#define SD3078_REG_CTRL1                0x0f
#define SD3078_REG_CTRL2                0x10
#define SD3078_REG_CTRL3                0x11

#define KEY_WRITE1              0x80
#define KEY_WRITE2              0x04
#define KEY_WRITE3              0x80

#define NUM_TIME_REGS   (SD3078_REG_YR - SD3078_REG_SC + 1)

/*
 * The sd3078 has write protection
 * and we can choose whether or not to use it.
 * Write protection is turned off by default.
 */
#define WRITE_PROTECT_EN        0

/*
 * In order to prevent arbitrary modification of the time register,
 * when modification of the register,
 * the "write" bit needs to be written in a certain order.
 * 1. set WRITE1 bit
 * 2. set WRITE2 bit
 * 3. set WRITE3 bit
 */
static void sd3078_enable_reg_write(struct regmap *regmap)
{
        regmap_update_bits(regmap, SD3078_REG_CTRL2, KEY_WRITE1, KEY_WRITE1);
        regmap_update_bits(regmap, SD3078_REG_CTRL1, KEY_WRITE2, KEY_WRITE2);
        regmap_update_bits(regmap, SD3078_REG_CTRL1, KEY_WRITE3, KEY_WRITE3);
}

#if WRITE_PROTECT_EN
/*
 * In order to prevent arbitrary modification of the time register,
 * we should disable the write function.
 * when disable write,
 * the "write" bit needs to be clear in a certain order.
 * 1. clear WRITE2 bit
 * 2. clear WRITE3 bit
 * 3. clear WRITE1 bit
 */
static void sd3078_disable_reg_write(struct regmap *regmap)
{
        regmap_update_bits(regmap, SD3078_REG_CTRL1, KEY_WRITE2, 0);
        regmap_update_bits(regmap, SD3078_REG_CTRL1, KEY_WRITE3, 0);
        regmap_update_bits(regmap, SD3078_REG_CTRL2, KEY_WRITE1, 0);
}
#endif

static int sd3078_rtc_read_time(struct device *dev, struct rtc_time *tm)
{
        unsigned char hour;
        unsigned char rtc_data[NUM_TIME_REGS] = {0};
        struct i2c_client *client = to_i2c_client(dev);
        struct regmap *regmap = i2c_get_clientdata(client);
        int ret;

        ret = regmap_bulk_read(regmap, SD3078_REG_SC, rtc_data, NUM_TIME_REGS);
        if (ret < 0) {
                dev_err(dev, "reading from RTC failed with err:%d\n", ret);
                return ret;
        }

        tm->tm_sec      = bcd2bin(rtc_data[SD3078_REG_SC] & 0x7F);
        tm->tm_min      = bcd2bin(rtc_data[SD3078_REG_MN] & 0x7F);

        /*
         * The sd3078 supports 12/24 hour mode.
         * When getting time,
         * we need to convert the 12 hour mode to the 24 hour mode.
         */
        hour = rtc_data[SD3078_REG_HR];
        if (hour & 0x80) /* 24H MODE */
                tm->tm_hour = bcd2bin(rtc_data[SD3078_REG_HR] & 0x3F);
        else if (hour & 0x20) /* 12H MODE PM */
                tm->tm_hour = bcd2bin(rtc_data[SD3078_REG_HR] & 0x1F) + 12;
        else /* 12H MODE AM */
                tm->tm_hour = bcd2bin(rtc_data[SD3078_REG_HR] & 0x1F);

        tm->tm_mday = bcd2bin(rtc_data[SD3078_REG_DM] & 0x3F);
        tm->tm_wday = rtc_data[SD3078_REG_DW] & 0x07;
        tm->tm_mon      = bcd2bin(rtc_data[SD3078_REG_MO] & 0x1F) - 1;
        tm->tm_year = bcd2bin(rtc_data[SD3078_REG_YR]) + 100;

        return 0;
}

static int sd3078_rtc_set_time(struct device *dev, struct rtc_time *tm)
{
        unsigned char rtc_data[NUM_TIME_REGS];
        struct i2c_client *client = to_i2c_client(dev);
        struct regmap *regmap = i2c_get_clientdata(client);
        int ret;

        rtc_data[SD3078_REG_SC] = bin2bcd(tm->tm_sec);
        rtc_data[SD3078_REG_MN] = bin2bcd(tm->tm_min);
        rtc_data[SD3078_REG_HR] = bin2bcd(tm->tm_hour) | 0x80;
        rtc_data[SD3078_REG_DM] = bin2bcd(tm->tm_mday);
        rtc_data[SD3078_REG_DW] = tm->tm_wday & 0x07;
        rtc_data[SD3078_REG_MO] = bin2bcd(tm->tm_mon) + 1;
        rtc_data[SD3078_REG_YR] = bin2bcd(tm->tm_year - 100);

#if WRITE_PROTECT_EN
        sd3078_enable_reg_write(regmap);
#endif

        ret = regmap_bulk_write(regmap, SD3078_REG_SC, rtc_data,
                                NUM_TIME_REGS);
        if (ret < 0) {
                dev_err(dev, "writing to RTC failed with err:%d\n", ret);
                return ret;
        }

#if WRITE_PROTECT_EN
        sd3078_disable_reg_write(regmap);
#endif

        return 0;
}

static const struct rtc_class_ops sd3078_rtc_ops = {
        .read_time      = sd3078_rtc_read_time,
        .set_time       = sd3078_rtc_set_time,
};

static const struct regmap_config regmap_config = {
        .reg_bits = 8,
        .val_bits = 8,
        .max_register = 0x11,
};

static int sd3078_probe(struct i2c_client *client)
{
        int ret;
        struct regmap *regmap;
        struct rtc_device *rtc;

        if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
                return -ENODEV;

        regmap = devm_regmap_init_i2c(client, &regmap_config);
        if (IS_ERR(regmap)) {
                dev_err(&client->dev, "regmap allocation failed\n");
                return PTR_ERR(regmap);
        }

        i2c_set_clientdata(client, regmap);

        rtc = devm_rtc_allocate_device(&client->dev);
        if (IS_ERR(rtc))
                return PTR_ERR(rtc);

        rtc->ops = &sd3078_rtc_ops;
        rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
        rtc->range_max = RTC_TIMESTAMP_END_2099;

        ret = devm_rtc_register_device(rtc);
        if (ret)
                return ret;

        sd3078_enable_reg_write(regmap);

        return 0;
}

static const struct i2c_device_id sd3078_id[] = {
        { "sd3078" },
        { }
};
MODULE_DEVICE_TABLE(i2c, sd3078_id);

static const __maybe_unused struct of_device_id rtc_dt_match[] = {
        { .compatible = "whwave,sd3078" },
        {},
};
MODULE_DEVICE_TABLE(of, rtc_dt_match);

static struct i2c_driver sd3078_driver = {
        .driver     = {
                .name   = "sd3078",
                .of_match_table = of_match_ptr(rtc_dt_match),
        },
        .probe      = sd3078_probe,
        .id_table   = sd3078_id,
};

module_i2c_driver(sd3078_driver);

MODULE_AUTHOR("Dianlong Li <long17.cool@163.com>");
MODULE_DESCRIPTION("SD3078 RTC driver");
MODULE_LICENSE("GPL v2");