// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2012 Sven Schnelle <svens@stackframe.org>

#include <linux/platform_device.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/rtc.h>
#include <linux/types.h>
#include <linux/bcd.h>
#include <linux/delay.h>
#include <linux/gpio/consumer.h>
#include <linux/slab.h>

#include <linux/io.h>

#define DS2404_STATUS_REG 0x200
#define DS2404_CONTROL_REG 0x201
#define DS2404_RTC_REG 0x202

#define DS2404_WRITE_SCRATCHPAD_CMD 0x0f
#define DS2404_READ_SCRATCHPAD_CMD 0xaa
#define DS2404_COPY_SCRATCHPAD_CMD 0x55
#define DS2404_READ_MEMORY_CMD 0xf0

#define DS2404_RST      0
#define DS2404_CLK      1
#define DS2404_DQ       2

struct ds2404 {
        struct device *dev;
        struct gpio_desc *rst_gpiod;
        struct gpio_desc *clk_gpiod;
        struct gpio_desc *dq_gpiod;
};

static int ds2404_gpio_map(struct ds2404 *chip, struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;

        /* This will de-assert RESET, declare this GPIO as GPIOD_ACTIVE_LOW */
        chip->rst_gpiod = devm_gpiod_get(dev, "rst", GPIOD_OUT_LOW);
        if (IS_ERR(chip->rst_gpiod))
                return PTR_ERR(chip->rst_gpiod);

        chip->clk_gpiod = devm_gpiod_get(dev, "clk", GPIOD_OUT_HIGH);
        if (IS_ERR(chip->clk_gpiod))
                return PTR_ERR(chip->clk_gpiod);

        chip->dq_gpiod = devm_gpiod_get(dev, "dq", GPIOD_ASIS);
        if (IS_ERR(chip->dq_gpiod))
                return PTR_ERR(chip->dq_gpiod);

        return 0;
}

static void ds2404_reset(struct ds2404 *chip)
{
        gpiod_set_value(chip->rst_gpiod, 1);
        udelay(1000);
        gpiod_set_value(chip->rst_gpiod, 0);
        gpiod_set_value(chip->clk_gpiod, 0);
        gpiod_direction_output(chip->dq_gpiod, 0);
        udelay(10);
}

static void ds2404_write_byte(struct ds2404 *chip, u8 byte)
{
        int i;

        gpiod_direction_output(chip->dq_gpiod, 1);
        for (i = 0; i < 8; i++) {
                gpiod_set_value(chip->dq_gpiod, byte & (1 << i));
                udelay(10);
                gpiod_set_value(chip->clk_gpiod, 1);
                udelay(10);
                gpiod_set_value(chip->clk_gpiod, 0);
                udelay(10);
        }
}

static u8 ds2404_read_byte(struct ds2404 *chip)
{
        int i;
        u8 ret = 0;

        gpiod_direction_input(chip->dq_gpiod);

        for (i = 0; i < 8; i++) {
                gpiod_set_value(chip->clk_gpiod, 0);
                udelay(10);
                if (gpiod_get_value(chip->dq_gpiod))
                        ret |= 1 << i;
                gpiod_set_value(chip->clk_gpiod, 1);
                udelay(10);
        }
        return ret;
}

static void ds2404_read_memory(struct ds2404 *chip, u16 offset,
                               int length, u8 *out)
{
        ds2404_reset(chip);
        ds2404_write_byte(chip, DS2404_READ_MEMORY_CMD);
        ds2404_write_byte(chip, offset & 0xff);
        ds2404_write_byte(chip, (offset >> 8) & 0xff);
        while (length--)
                *out++ = ds2404_read_byte(chip);
}

static void ds2404_write_memory(struct ds2404 *chip, u16 offset,
                                int length, u8 *out)
{
        int i;
        u8 ta01, ta02, es;

        ds2404_reset(chip);
        ds2404_write_byte(chip, DS2404_WRITE_SCRATCHPAD_CMD);
        ds2404_write_byte(chip, offset & 0xff);
        ds2404_write_byte(chip, (offset >> 8) & 0xff);

        for (i = 0; i < length; i++)
                ds2404_write_byte(chip, out[i]);

        ds2404_reset(chip);
        ds2404_write_byte(chip, DS2404_READ_SCRATCHPAD_CMD);

        ta01 = ds2404_read_byte(chip);
        ta02 = ds2404_read_byte(chip);
        es = ds2404_read_byte(chip);

        for (i = 0; i < length; i++) {
                if (out[i] != ds2404_read_byte(chip)) {
                        dev_err(chip->dev, "read invalid data\n");
                        return;
                }
        }

        ds2404_reset(chip);
        ds2404_write_byte(chip, DS2404_COPY_SCRATCHPAD_CMD);
        ds2404_write_byte(chip, ta01);
        ds2404_write_byte(chip, ta02);
        ds2404_write_byte(chip, es);

        while (gpiod_get_value(chip->dq_gpiod))
                ;
}

static void ds2404_enable_osc(struct ds2404 *chip)
{
        u8 in[1] = { 0x10 }; /* enable oscillator */

        ds2404_write_memory(chip, 0x201, 1, in);
}

static int ds2404_read_time(struct device *dev, struct rtc_time *dt)
{
        struct ds2404 *chip = dev_get_drvdata(dev);
        unsigned long time = 0;
        __le32 hw_time = 0;

        ds2404_read_memory(chip, 0x203, 4, (u8 *)&hw_time);
        time = le32_to_cpu(hw_time);

        rtc_time64_to_tm(time, dt);
        return 0;
}

static int ds2404_set_time(struct device *dev, struct rtc_time *dt)
{
        struct ds2404 *chip = dev_get_drvdata(dev);
        u32 time = cpu_to_le32(rtc_tm_to_time64(dt));
        ds2404_write_memory(chip, 0x203, 4, (u8 *)&time);
        return 0;
}

static const struct rtc_class_ops ds2404_rtc_ops = {
        .read_time      = ds2404_read_time,
        .set_time       = ds2404_set_time,
};

static int rtc_probe(struct platform_device *pdev)
{
        struct ds2404 *chip;
        struct rtc_device *rtc;
        int retval = -EBUSY;

        chip = devm_kzalloc(&pdev->dev, sizeof(struct ds2404), GFP_KERNEL);
        if (!chip)
                return -ENOMEM;

        chip->dev = &pdev->dev;

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

        retval = ds2404_gpio_map(chip, pdev);
        if (retval)
                return retval;

        platform_set_drvdata(pdev, chip);

        rtc->ops = &ds2404_rtc_ops;
        rtc->range_max = U32_MAX;

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

        ds2404_enable_osc(chip);
        return 0;
}

static struct platform_driver rtc_device_driver = {
        .probe  = rtc_probe,
        .driver = {
                .name   = "ds2404",
        },
};
module_platform_driver(rtc_device_driver);

MODULE_DESCRIPTION("DS2404 RTC");
MODULE_AUTHOR("Sven Schnelle");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:ds2404");