// SPDX-License-Identifier: GPL-2.0-only
/*
 * ST M48T86 / Dallas DS12887 RTC driver
 * Copyright (c) 2006 Tower Technologies
 *
 * Author: Alessandro Zummo <a.zummo@towertech.it>
 *
 * This drivers only supports the clock running in BCD and 24H mode.
 * If it will be ever adapted to binary and 12H mode, care must be taken
 * to not introduce bugs.
 */

#include <linux/module.h>
#include <linux/mod_devicetable.h>
#include <linux/rtc.h>
#include <linux/platform_device.h>
#include <linux/bcd.h>
#include <linux/io.h>

#define M48T86_SEC              0x00
#define M48T86_SECALRM          0x01
#define M48T86_MIN              0x02
#define M48T86_MINALRM          0x03
#define M48T86_HOUR             0x04
#define M48T86_HOURALRM         0x05
#define M48T86_DOW              0x06 /* 1 = sunday */
#define M48T86_DOM              0x07
#define M48T86_MONTH            0x08 /* 1 - 12 */
#define M48T86_YEAR             0x09 /* 0 - 99 */
#define M48T86_A                0x0a
#define M48T86_B                0x0b
#define M48T86_B_SET            BIT(7)
#define M48T86_B_DM             BIT(2)
#define M48T86_B_H24            BIT(1)
#define M48T86_C                0x0c
#define M48T86_D                0x0d
#define M48T86_D_VRT            BIT(7)
#define M48T86_NVRAM(x)         (0x0e + (x))
#define M48T86_NVRAM_LEN        114

struct m48t86_rtc_info {
        void __iomem *index_reg;
        void __iomem *data_reg;
};

static unsigned char m48t86_readb(struct device *dev, unsigned long addr)
{
        struct m48t86_rtc_info *info = dev_get_drvdata(dev);
        unsigned char value;

        writeb(addr, info->index_reg);
        value = readb(info->data_reg);

        return value;
}

static void m48t86_writeb(struct device *dev,
                          unsigned char value, unsigned long addr)
{
        struct m48t86_rtc_info *info = dev_get_drvdata(dev);

        writeb(addr, info->index_reg);
        writeb(value, info->data_reg);
}

static int m48t86_rtc_read_time(struct device *dev, struct rtc_time *tm)
{
        unsigned char reg;

        reg = m48t86_readb(dev, M48T86_B);

        if (reg & M48T86_B_DM) {
                /* data (binary) mode */
                tm->tm_sec      = m48t86_readb(dev, M48T86_SEC);
                tm->tm_min      = m48t86_readb(dev, M48T86_MIN);
                tm->tm_hour     = m48t86_readb(dev, M48T86_HOUR) & 0x3f;
                tm->tm_mday     = m48t86_readb(dev, M48T86_DOM);
                /* tm_mon is 0-11 */
                tm->tm_mon      = m48t86_readb(dev, M48T86_MONTH) - 1;
                tm->tm_year     = m48t86_readb(dev, M48T86_YEAR) + 100;
                tm->tm_wday     = m48t86_readb(dev, M48T86_DOW);
        } else {
                /* bcd mode */
                tm->tm_sec      = bcd2bin(m48t86_readb(dev, M48T86_SEC));
                tm->tm_min      = bcd2bin(m48t86_readb(dev, M48T86_MIN));
                tm->tm_hour     = bcd2bin(m48t86_readb(dev, M48T86_HOUR) &
                                          0x3f);
                tm->tm_mday     = bcd2bin(m48t86_readb(dev, M48T86_DOM));
                /* tm_mon is 0-11 */
                tm->tm_mon      = bcd2bin(m48t86_readb(dev, M48T86_MONTH)) - 1;
                tm->tm_year     = bcd2bin(m48t86_readb(dev, M48T86_YEAR)) + 100;
                tm->tm_wday     = bcd2bin(m48t86_readb(dev, M48T86_DOW));
        }

        /* correct the hour if the clock is in 12h mode */
        if (!(reg & M48T86_B_H24))
                if (m48t86_readb(dev, M48T86_HOUR) & 0x80)
                        tm->tm_hour += 12;

        return 0;
}

static int m48t86_rtc_set_time(struct device *dev, struct rtc_time *tm)
{
        unsigned char reg;

        reg = m48t86_readb(dev, M48T86_B);

        /* update flag and 24h mode */
        reg |= M48T86_B_SET | M48T86_B_H24;
        m48t86_writeb(dev, reg, M48T86_B);

        if (reg & M48T86_B_DM) {
                /* data (binary) mode */
                m48t86_writeb(dev, tm->tm_sec, M48T86_SEC);
                m48t86_writeb(dev, tm->tm_min, M48T86_MIN);
                m48t86_writeb(dev, tm->tm_hour, M48T86_HOUR);
                m48t86_writeb(dev, tm->tm_mday, M48T86_DOM);
                m48t86_writeb(dev, tm->tm_mon + 1, M48T86_MONTH);
                m48t86_writeb(dev, tm->tm_year % 100, M48T86_YEAR);
                m48t86_writeb(dev, tm->tm_wday, M48T86_DOW);
        } else {
                /* bcd mode */
                m48t86_writeb(dev, bin2bcd(tm->tm_sec), M48T86_SEC);
                m48t86_writeb(dev, bin2bcd(tm->tm_min), M48T86_MIN);
                m48t86_writeb(dev, bin2bcd(tm->tm_hour), M48T86_HOUR);
                m48t86_writeb(dev, bin2bcd(tm->tm_mday), M48T86_DOM);
                m48t86_writeb(dev, bin2bcd(tm->tm_mon + 1), M48T86_MONTH);
                m48t86_writeb(dev, bin2bcd(tm->tm_year % 100), M48T86_YEAR);
                m48t86_writeb(dev, bin2bcd(tm->tm_wday), M48T86_DOW);
        }

        /* update ended */
        reg &= ~M48T86_B_SET;
        m48t86_writeb(dev, reg, M48T86_B);

        return 0;
}

static int m48t86_rtc_proc(struct device *dev, struct seq_file *seq)
{
        unsigned char reg;

        reg = m48t86_readb(dev, M48T86_B);

        seq_printf(seq, "mode\t\t: %s\n",
                   (reg & M48T86_B_DM) ? "binary" : "bcd");

        reg = m48t86_readb(dev, M48T86_D);

        seq_printf(seq, "battery\t\t: %s\n",
                   (reg & M48T86_D_VRT) ? "ok" : "exhausted");

        return 0;
}

static const struct rtc_class_ops m48t86_rtc_ops = {
        .read_time      = m48t86_rtc_read_time,
        .set_time       = m48t86_rtc_set_time,
        .proc           = m48t86_rtc_proc,
};

static int m48t86_nvram_read(void *priv, unsigned int off, void *buf,
                             size_t count)
{
        struct device *dev = priv;
        unsigned int i;

        for (i = 0; i < count; i++)
                ((u8 *)buf)[i] = m48t86_readb(dev, M48T86_NVRAM(off + i));

        return 0;
}

static int m48t86_nvram_write(void *priv, unsigned int off, void *buf,
                              size_t count)
{
        struct device *dev = priv;
        unsigned int i;

        for (i = 0; i < count; i++)
                m48t86_writeb(dev, ((u8 *)buf)[i], M48T86_NVRAM(off + i));

        return 0;
}

/*
 * The RTC is an optional feature at purchase time on some Technologic Systems
 * boards. Verify that it actually exists by checking if the last two bytes
 * of the NVRAM can be changed.
 *
 * This is based on the method used in their rtc7800.c example.
 */
static bool m48t86_verify_chip(struct platform_device *pdev)
{
        unsigned int offset0 = M48T86_NVRAM(M48T86_NVRAM_LEN - 2);
        unsigned int offset1 = M48T86_NVRAM(M48T86_NVRAM_LEN - 1);
        unsigned char tmp0, tmp1;

        tmp0 = m48t86_readb(&pdev->dev, offset0);
        tmp1 = m48t86_readb(&pdev->dev, offset1);

        m48t86_writeb(&pdev->dev, 0x00, offset0);
        m48t86_writeb(&pdev->dev, 0x55, offset1);
        if (m48t86_readb(&pdev->dev, offset1) == 0x55) {
                m48t86_writeb(&pdev->dev, 0xaa, offset1);
                if (m48t86_readb(&pdev->dev, offset1) == 0xaa &&
                    m48t86_readb(&pdev->dev, offset0) == 0x00) {
                        m48t86_writeb(&pdev->dev, tmp0, offset0);
                        m48t86_writeb(&pdev->dev, tmp1, offset1);

                        return true;
                }
        }
        return false;
}

static int m48t86_rtc_probe(struct platform_device *pdev)
{
        struct m48t86_rtc_info *info;
        struct rtc_device *rtc;
        unsigned char reg;
        int err;
        struct nvmem_config m48t86_nvmem_cfg = {
                .name = "m48t86_nvram",
                .word_size = 1,
                .stride = 1,
                .size = M48T86_NVRAM_LEN,
                .reg_read = m48t86_nvram_read,
                .reg_write = m48t86_nvram_write,
                .priv = &pdev->dev,
        };

        info = devm_kzalloc(&pdev->dev, sizeof(*info), GFP_KERNEL);
        if (!info)
                return -ENOMEM;

        info->index_reg = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(info->index_reg))
                return PTR_ERR(info->index_reg);

        info->data_reg = devm_platform_ioremap_resource(pdev, 1);
        if (IS_ERR(info->data_reg))
                return PTR_ERR(info->data_reg);

        dev_set_drvdata(&pdev->dev, info);

        if (!m48t86_verify_chip(pdev)) {
                dev_info(&pdev->dev, "RTC not present\n");
                return -ENODEV;
        }

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

        rtc->ops = &m48t86_rtc_ops;

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

        devm_rtc_nvmem_register(rtc, &m48t86_nvmem_cfg);

        /* read battery status */
        reg = m48t86_readb(&pdev->dev, M48T86_D);
        dev_info(&pdev->dev, "battery %s\n",
                 (reg & M48T86_D_VRT) ? "ok" : "exhausted");

        return 0;
}

static const struct of_device_id m48t86_rtc_of_ids[] = {
        { .compatible = "st,m48t86" },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, m48t86_rtc_of_ids);

static struct platform_driver m48t86_rtc_platform_driver = {
        .driver         = {
                .name   = "rtc-m48t86",
                .of_match_table = m48t86_rtc_of_ids,
        },
        .probe          = m48t86_rtc_probe,
};

module_platform_driver(m48t86_rtc_platform_driver);

MODULE_AUTHOR("Alessandro Zummo <a.zummo@towertech.it>");
MODULE_DESCRIPTION("M48T86 RTC driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:rtc-m48t86");