// SPDX-License-Identifier: GPL-2.0-only
/*
 * Dallas DS1302 RTC Support
 *
 *  Copyright (C) 2002 David McCullough
 *  Copyright (C) 2003 - 2007 Paul Mundt
 */

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

#define RTC_CMD_READ    0x81            /* Read command */
#define RTC_CMD_WRITE   0x80            /* Write command */

#define RTC_CMD_WRITE_ENABLE    0x00            /* Write enable */
#define RTC_CMD_WRITE_DISABLE   0x80            /* Write disable */

#define RTC_ADDR_RAM0   0x20            /* Address of RAM0 */
#define RTC_ADDR_TCR    0x08            /* Address of trickle charge register */
#define RTC_CLCK_BURST  0x1F            /* Address of clock burst */
#define RTC_CLCK_LEN    0x08            /* Size of clock burst */
#define RTC_ADDR_CTRL   0x07            /* Address of control register */
#define RTC_ADDR_YEAR   0x06            /* Address of year register */
#define RTC_ADDR_DAY    0x05            /* Address of day of week register */
#define RTC_ADDR_MON    0x04            /* Address of month register */
#define RTC_ADDR_DATE   0x03            /* Address of day of month register */
#define RTC_ADDR_HOUR   0x02            /* Address of hour register */
#define RTC_ADDR_MIN    0x01            /* Address of minute register */
#define RTC_ADDR_SEC    0x00            /* Address of second register */

static int ds1302_rtc_set_time(struct device *dev, struct rtc_time *time)
{
        struct spi_device       *spi = dev_get_drvdata(dev);
        u8              buf[1 + RTC_CLCK_LEN];
        u8              *bp;
        int             status;

        /* Enable writing */
        bp = buf;
        *bp++ = RTC_ADDR_CTRL << 1 | RTC_CMD_WRITE;
        *bp++ = RTC_CMD_WRITE_ENABLE;

        status = spi_write_then_read(spi, buf, 2,
                        NULL, 0);
        if (status)
                return status;

        /* Write registers starting at the first time/date address. */
        bp = buf;
        *bp++ = RTC_CLCK_BURST << 1 | RTC_CMD_WRITE;

        *bp++ = bin2bcd(time->tm_sec);
        *bp++ = bin2bcd(time->tm_min);
        *bp++ = bin2bcd(time->tm_hour);
        *bp++ = bin2bcd(time->tm_mday);
        *bp++ = bin2bcd(time->tm_mon + 1);
        *bp++ = time->tm_wday + 1;
        *bp++ = bin2bcd(time->tm_year % 100);
        *bp++ = RTC_CMD_WRITE_DISABLE;

        /* use write-then-read since dma from stack is nonportable */
        return spi_write_then_read(spi, buf, sizeof(buf),
                        NULL, 0);
}

static int ds1302_rtc_get_time(struct device *dev, struct rtc_time *time)
{
        struct spi_device       *spi = dev_get_drvdata(dev);
        u8              addr = RTC_CLCK_BURST << 1 | RTC_CMD_READ;
        u8              buf[RTC_CLCK_LEN - 1];
        int             status;

        /* Use write-then-read to get all the date/time registers
         * since dma from stack is nonportable
         */
        status = spi_write_then_read(spi, &addr, sizeof(addr),
                        buf, sizeof(buf));
        if (status < 0)
                return status;

        /* Decode the registers */
        time->tm_sec = bcd2bin(buf[RTC_ADDR_SEC]);
        time->tm_min = bcd2bin(buf[RTC_ADDR_MIN]);
        time->tm_hour = bcd2bin(buf[RTC_ADDR_HOUR]);
        time->tm_wday = buf[RTC_ADDR_DAY] - 1;
        time->tm_mday = bcd2bin(buf[RTC_ADDR_DATE]);
        time->tm_mon = bcd2bin(buf[RTC_ADDR_MON]) - 1;
        time->tm_year = bcd2bin(buf[RTC_ADDR_YEAR]) + 100;

        return 0;
}

static const struct rtc_class_ops ds1302_rtc_ops = {
        .read_time      = ds1302_rtc_get_time,
        .set_time       = ds1302_rtc_set_time,
};

static int ds1302_probe(struct spi_device *spi)
{
        struct rtc_device       *rtc;
        u8              addr;
        u8              buf[4];
        u8              *bp;
        int             status;

        /* Sanity check board setup data.  This may be hooked up
         * in 3wire mode, but we don't care.  Note that unless
         * there's an inverter in place, this needs SPI_CS_HIGH!
         */
        if (spi->bits_per_word && (spi->bits_per_word != 8)) {
                dev_err(&spi->dev, "bad word length\n");
                return -EINVAL;
        } else if (spi->max_speed_hz > 2000000) {
                dev_err(&spi->dev, "speed is too high\n");
                return -EINVAL;
        } else if (spi->mode & SPI_CPHA) {
                dev_err(&spi->dev, "bad mode\n");
                return -EINVAL;
        }

        addr = RTC_ADDR_CTRL << 1 | RTC_CMD_READ;
        status = spi_write_then_read(spi, &addr, sizeof(addr), buf, 1);
        if (status < 0) {
                dev_err(&spi->dev, "control register read error %d\n",
                                status);
                return status;
        }

        if ((buf[0] & ~RTC_CMD_WRITE_DISABLE) != 0) {
                status = spi_write_then_read(spi, &addr, sizeof(addr), buf, 1);
                if (status < 0) {
                        dev_err(&spi->dev, "control register read error %d\n",
                                        status);
                        return status;
                }

                if ((buf[0] & ~RTC_CMD_WRITE_DISABLE) != 0) {
                        dev_err(&spi->dev, "junk in control register\n");
                        return -ENODEV;
                }
        }
        if (buf[0] == 0) {
                bp = buf;
                *bp++ = RTC_ADDR_CTRL << 1 | RTC_CMD_WRITE;
                *bp++ = RTC_CMD_WRITE_DISABLE;

                status = spi_write_then_read(spi, buf, 2, NULL, 0);
                if (status < 0) {
                        dev_err(&spi->dev, "control register write error %d\n",
                                        status);
                        return status;
                }

                addr = RTC_ADDR_CTRL << 1 | RTC_CMD_READ;
                status = spi_write_then_read(spi, &addr, sizeof(addr), buf, 1);
                if (status < 0) {
                        dev_err(&spi->dev,
                                        "error %d reading control register\n",
                                        status);
                        return status;
                }

                if (buf[0] != RTC_CMD_WRITE_DISABLE) {
                        dev_err(&spi->dev, "failed to detect chip\n");
                        return -ENODEV;
                }
        }

        spi_set_drvdata(spi, spi);

        rtc = devm_rtc_device_register(&spi->dev, "ds1302",
                        &ds1302_rtc_ops, THIS_MODULE);
        if (IS_ERR(rtc)) {
                status = PTR_ERR(rtc);
                dev_err(&spi->dev, "error %d registering rtc\n", status);
                return status;
        }

        return 0;
}

#ifdef CONFIG_OF
static const struct of_device_id ds1302_dt_ids[] = {
        { .compatible = "maxim,ds1302", },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, ds1302_dt_ids);
#endif

static const struct spi_device_id ds1302_spi_ids[] = {
        { .name = "ds1302", },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(spi, ds1302_spi_ids);

static struct spi_driver ds1302_driver = {
        .driver.name    = "rtc-ds1302",
        .driver.of_match_table = of_match_ptr(ds1302_dt_ids),
        .probe          = ds1302_probe,
        .id_table       = ds1302_spi_ids,
};

module_spi_driver(ds1302_driver);

MODULE_DESCRIPTION("Dallas DS1302 RTC driver");
MODULE_AUTHOR("Paul Mundt, David McCullough");
MODULE_LICENSE("GPL v2");