// SPDX-License-Identifier: GPL-2.0-only
/*
 * rtc class driver for the Maxim MAX6900 chip
 *
 * Copyright (c) 2007 MontaVista, Software, Inc.
 *
 * Author: Dale Farnsworth <dale@farnsworth.org>
 *
 * based on previously existing rtc class drivers
 */

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

/*
 * register indices
 */
#define MAX6900_REG_SC                  0       /* seconds      00-59 */
#define MAX6900_REG_MN                  1       /* minutes      00-59 */
#define MAX6900_REG_HR                  2       /* hours        00-23 */
#define MAX6900_REG_DT                  3       /* day of month 00-31 */
#define MAX6900_REG_MO                  4       /* month        01-12 */
#define MAX6900_REG_DW                  5       /* day of week   1-7  */
#define MAX6900_REG_YR                  6       /* year         00-99 */
#define MAX6900_REG_CT                  7       /* control */
                                                /* register 8 is undocumented */
#define MAX6900_REG_CENTURY             9       /* century */
#define MAX6900_REG_LEN                 10

#define MAX6900_BURST_LEN               8       /* can burst r/w first 8 regs */

#define MAX6900_REG_CT_WP               (1 << 7)        /* Write Protect */

/*
 * register read/write commands
 */
#define MAX6900_REG_CONTROL_WRITE       0x8e
#define MAX6900_REG_CENTURY_WRITE       0x92
#define MAX6900_REG_CENTURY_READ        0x93
#define MAX6900_REG_RESERVED_READ       0x96
#define MAX6900_REG_BURST_WRITE         0xbe
#define MAX6900_REG_BURST_READ          0xbf

#define MAX6900_IDLE_TIME_AFTER_WRITE   3       /* specification says 2.5 mS */

static struct i2c_driver max6900_driver;

static int max6900_i2c_read_regs(struct i2c_client *client, u8 *buf)
{
        u8 reg_burst_read[1] = { MAX6900_REG_BURST_READ };
        u8 reg_century_read[1] = { MAX6900_REG_CENTURY_READ };
        struct i2c_msg msgs[4] = {
                {
                 .addr = client->addr,
                 .flags = 0,    /* write */
                 .len = sizeof(reg_burst_read),
                 .buf = reg_burst_read}
                ,
                {
                 .addr = client->addr,
                 .flags = I2C_M_RD,
                 .len = MAX6900_BURST_LEN,
                 .buf = buf}
                ,
                {
                 .addr = client->addr,
                 .flags = 0,    /* write */
                 .len = sizeof(reg_century_read),
                 .buf = reg_century_read}
                ,
                {
                 .addr = client->addr,
                 .flags = I2C_M_RD,
                 .len = sizeof(buf[MAX6900_REG_CENTURY]),
                 .buf = &buf[MAX6900_REG_CENTURY]
                 }
        };
        int rc;

        rc = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
        if (rc != ARRAY_SIZE(msgs)) {
                dev_err(&client->dev, "%s: register read failed\n", __func__);
                return -EIO;
        }
        return 0;
}

static int max6900_i2c_write_regs(struct i2c_client *client, u8 const *buf)
{
        u8 i2c_century_buf[1 + 1] = { MAX6900_REG_CENTURY_WRITE };
        struct i2c_msg century_msgs[1] = {
                {
                 .addr = client->addr,
                 .flags = 0,    /* write */
                 .len = sizeof(i2c_century_buf),
                 .buf = i2c_century_buf}
        };
        u8 i2c_burst_buf[MAX6900_BURST_LEN + 1] = { MAX6900_REG_BURST_WRITE };
        struct i2c_msg burst_msgs[1] = {
                {
                 .addr = client->addr,
                 .flags = 0,    /* write */
                 .len = sizeof(i2c_burst_buf),
                 .buf = i2c_burst_buf}
        };
        int rc;

        /*
         * We have to make separate calls to i2c_transfer because of
         * the need to delay after each write to the chip.  Also,
         * we write the century byte first, since we set the write-protect
         * bit as part of the burst write.
         */
        i2c_century_buf[1] = buf[MAX6900_REG_CENTURY];

        rc = i2c_transfer(client->adapter, century_msgs,
                          ARRAY_SIZE(century_msgs));
        if (rc != ARRAY_SIZE(century_msgs))
                goto write_failed;

        msleep(MAX6900_IDLE_TIME_AFTER_WRITE);

        memcpy(&i2c_burst_buf[1], buf, MAX6900_BURST_LEN);

        rc = i2c_transfer(client->adapter, burst_msgs, ARRAY_SIZE(burst_msgs));
        if (rc != ARRAY_SIZE(burst_msgs))
                goto write_failed;
        msleep(MAX6900_IDLE_TIME_AFTER_WRITE);

        return 0;

 write_failed:
        dev_err(&client->dev, "%s: register write failed\n", __func__);
        return -EIO;
}

static int max6900_rtc_read_time(struct device *dev, struct rtc_time *tm)
{
        struct i2c_client *client = to_i2c_client(dev);
        int rc;
        u8 regs[MAX6900_REG_LEN];

        rc = max6900_i2c_read_regs(client, regs);
        if (rc < 0)
                return rc;

        tm->tm_sec = bcd2bin(regs[MAX6900_REG_SC]);
        tm->tm_min = bcd2bin(regs[MAX6900_REG_MN]);
        tm->tm_hour = bcd2bin(regs[MAX6900_REG_HR] & 0x3f);
        tm->tm_mday = bcd2bin(regs[MAX6900_REG_DT]);
        tm->tm_mon = bcd2bin(regs[MAX6900_REG_MO]) - 1;
        tm->tm_year = bcd2bin(regs[MAX6900_REG_YR]) +
                      bcd2bin(regs[MAX6900_REG_CENTURY]) * 100 - 1900;
        tm->tm_wday = bcd2bin(regs[MAX6900_REG_DW]);

        return 0;
}

static int max6900_i2c_clear_write_protect(struct i2c_client *client)
{
        return i2c_smbus_write_byte_data(client, MAX6900_REG_CONTROL_WRITE, 0);
}

static int max6900_rtc_set_time(struct device *dev, struct rtc_time *tm)
{
        struct i2c_client *client = to_i2c_client(dev);
        u8 regs[MAX6900_REG_LEN];
        int rc;

        rc = max6900_i2c_clear_write_protect(client);
        if (rc < 0)
                return rc;

        regs[MAX6900_REG_SC] = bin2bcd(tm->tm_sec);
        regs[MAX6900_REG_MN] = bin2bcd(tm->tm_min);
        regs[MAX6900_REG_HR] = bin2bcd(tm->tm_hour);
        regs[MAX6900_REG_DT] = bin2bcd(tm->tm_mday);
        regs[MAX6900_REG_MO] = bin2bcd(tm->tm_mon + 1);
        regs[MAX6900_REG_DW] = bin2bcd(tm->tm_wday);
        regs[MAX6900_REG_YR] = bin2bcd(tm->tm_year % 100);
        regs[MAX6900_REG_CENTURY] = bin2bcd((tm->tm_year + 1900) / 100);
        /* set write protect */
        regs[MAX6900_REG_CT] = MAX6900_REG_CT_WP;

        rc = max6900_i2c_write_regs(client, regs);
        if (rc < 0)
                return rc;

        return 0;
}

static const struct rtc_class_ops max6900_rtc_ops = {
        .read_time = max6900_rtc_read_time,
        .set_time = max6900_rtc_set_time,
};

static int max6900_probe(struct i2c_client *client)
{
        struct rtc_device *rtc;

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

        rtc = devm_rtc_device_register(&client->dev, max6900_driver.driver.name,
                                        &max6900_rtc_ops, THIS_MODULE);
        if (IS_ERR(rtc))
                return PTR_ERR(rtc);

        i2c_set_clientdata(client, rtc);

        return 0;
}

static const struct i2c_device_id max6900_id[] = {
        { "max6900" },
        { }
};
MODULE_DEVICE_TABLE(i2c, max6900_id);

static struct i2c_driver max6900_driver = {
        .driver = {
                   .name = "rtc-max6900",
                   },
        .probe = max6900_probe,
        .id_table = max6900_id,
};

module_i2c_driver(max6900_driver);

MODULE_DESCRIPTION("Maxim MAX6900 RTC driver");
MODULE_AUTHOR("Dale Farnsworth <dale@farnsworth.org>");
MODULE_LICENSE("GPL");