// SPDX-License-Identifier: GPL-2.0
/*
 * An rtc/i2c driver for the Dallas DS1672
 * Copyright 2005-06 Tower Technologies
 *
 * Author: Alessandro Zummo <a.zummo@towertech.it>
 */

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

/* Registers */

#define DS1672_REG_CNT_BASE     0
#define DS1672_REG_CONTROL      4
#define DS1672_REG_TRICKLE      5

#define DS1672_REG_CONTROL_EOSC 0x80

/*
 * In the routines that deal directly with the ds1672 hardware, we use
 * rtc_time -- month 0-11, hour 0-23, yr = calendar year-epoch
 * Time is set to UTC.
 */
static int ds1672_read_time(struct device *dev, struct rtc_time *tm)
{
        struct i2c_client *client = to_i2c_client(dev);
        unsigned long time;
        unsigned char addr = DS1672_REG_CONTROL;
        unsigned char buf[4];

        struct i2c_msg msgs[] = {
                {/* setup read ptr */
                        .addr = client->addr,
                        .len = 1,
                        .buf = &addr
                },
                {/* read date */
                        .addr = client->addr,
                        .flags = I2C_M_RD,
                        .len = 1,
                        .buf = buf
                },
        };

        /* read control register */
        if ((i2c_transfer(client->adapter, &msgs[0], 2)) != 2) {
                dev_warn(&client->dev, "Unable to read the control register\n");
                return -EIO;
        }

        if (buf[0] & DS1672_REG_CONTROL_EOSC) {
                dev_warn(&client->dev, "Oscillator not enabled. Set time to enable.\n");
                return -EINVAL;
        }

        addr = DS1672_REG_CNT_BASE;
        msgs[1].len = 4;

        /* read date registers */
        if ((i2c_transfer(client->adapter, &msgs[0], 2)) != 2) {
                dev_err(&client->dev, "%s: read error\n", __func__);
                return -EIO;
        }

        dev_dbg(&client->dev,
                "%s: raw read data - counters=%02x,%02x,%02x,%02x\n",
                __func__, buf[0], buf[1], buf[2], buf[3]);

        time = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
               (buf[1] << 8) | buf[0];

        rtc_time64_to_tm(time, tm);

        dev_dbg(&client->dev, "%s: tm is %ptR\n", __func__, tm);

        return 0;
}

static int ds1672_set_time(struct device *dev, struct rtc_time *tm)
{
        struct i2c_client *client = to_i2c_client(dev);
        int xfer;
        unsigned char buf[6];
        unsigned long secs = rtc_tm_to_time64(tm);

        buf[0] = DS1672_REG_CNT_BASE;
        buf[1] = secs & 0x000000FF;
        buf[2] = (secs & 0x0000FF00) >> 8;
        buf[3] = (secs & 0x00FF0000) >> 16;
        buf[4] = (secs & 0xFF000000) >> 24;
        buf[5] = 0;             /* set control reg to enable counting */

        xfer = i2c_master_send(client, buf, 6);
        if (xfer != 6) {
                dev_err(&client->dev, "%s: send: %d\n", __func__, xfer);
                return -EIO;
        }

        return 0;
}

static const struct rtc_class_ops ds1672_rtc_ops = {
        .read_time = ds1672_read_time,
        .set_time = ds1672_set_time,
};

static int ds1672_probe(struct i2c_client *client)
{
        int err = 0;
        struct rtc_device *rtc;

        dev_dbg(&client->dev, "%s\n", __func__);

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

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

        rtc->ops = &ds1672_rtc_ops;
        rtc->range_max = U32_MAX;

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

        i2c_set_clientdata(client, rtc);

        return 0;
}

static const struct i2c_device_id ds1672_id[] = {
        { "ds1672" },
        { }
};
MODULE_DEVICE_TABLE(i2c, ds1672_id);

static const __maybe_unused struct of_device_id ds1672_of_match[] = {
        { .compatible = "dallas,ds1672" },
        { }
};
MODULE_DEVICE_TABLE(of, ds1672_of_match);

static struct i2c_driver ds1672_driver = {
        .driver = {
                   .name = "rtc-ds1672",
                   .of_match_table = of_match_ptr(ds1672_of_match),
        },
        .probe = ds1672_probe,
        .id_table = ds1672_id,
};

module_i2c_driver(ds1672_driver);

MODULE_AUTHOR("Alessandro Zummo <a.zummo@towertech.it>");
MODULE_DESCRIPTION("Dallas/Maxim DS1672 timekeeper driver");
MODULE_LICENSE("GPL");