// SPDX-License-Identifier: GPL-2.0-only
/*
 * Dallas DS1216 RTC driver
 *
 * Copyright (c) 2007 Thomas Bogendoerfer
 *
 */

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

struct ds1216_regs {
        u8 tsec;
        u8 sec;
        u8 min;
        u8 hour;
        u8 wday;
        u8 mday;
        u8 month;
        u8 year;
};

#define DS1216_HOUR_1224        (1 << 7)
#define DS1216_HOUR_AMPM        (1 << 5)

struct ds1216_priv {
        struct rtc_device *rtc;
        void __iomem *ioaddr;
};

static const u8 magic[] = {
        0xc5, 0x3a, 0xa3, 0x5c, 0xc5, 0x3a, 0xa3, 0x5c
};

/*
 * Read the 64 bit we'd like to have - It a series
 * of 64 bits showing up in the LSB of the base register.
 *
 */
static void ds1216_read(u8 __iomem *ioaddr, u8 *buf)
{
        unsigned char c;
        int i, j;

        for (i = 0; i < 8; i++) {
                c = 0;
                for (j = 0; j < 8; j++)
                        c |= (readb(ioaddr) & 0x1) << j;
                buf[i] = c;
        }
}

static void ds1216_write(u8 __iomem *ioaddr, const u8 *buf)
{
        unsigned char c;
        int i, j;

        for (i = 0; i < 8; i++) {
                c = buf[i];
                for (j = 0; j < 8; j++) {
                        writeb(c, ioaddr);
                        c = c >> 1;
                }
        }
}

static void ds1216_switch_ds_to_clock(u8 __iomem *ioaddr)
{
        /* Reset magic pointer */
        readb(ioaddr);
        /* Write 64 bit magic to DS1216 */
        ds1216_write(ioaddr, magic);
}

static int ds1216_rtc_read_time(struct device *dev, struct rtc_time *tm)
{
        struct ds1216_priv *priv = dev_get_drvdata(dev);
        struct ds1216_regs regs;

        ds1216_switch_ds_to_clock(priv->ioaddr);
        ds1216_read(priv->ioaddr, (u8 *)&regs);

        tm->tm_sec = bcd2bin(regs.sec);
        tm->tm_min = bcd2bin(regs.min);
        if (regs.hour & DS1216_HOUR_1224) {
                /* AM/PM mode */
                tm->tm_hour = bcd2bin(regs.hour & 0x1f);
                if (regs.hour & DS1216_HOUR_AMPM)
                        tm->tm_hour += 12;
        } else
                tm->tm_hour = bcd2bin(regs.hour & 0x3f);
        tm->tm_wday = (regs.wday & 7) - 1;
        tm->tm_mday = bcd2bin(regs.mday & 0x3f);
        tm->tm_mon = bcd2bin(regs.month & 0x1f);
        tm->tm_year = bcd2bin(regs.year);
        if (tm->tm_year < 70)
                tm->tm_year += 100;

        return 0;
}

static int ds1216_rtc_set_time(struct device *dev, struct rtc_time *tm)
{
        struct ds1216_priv *priv = dev_get_drvdata(dev);
        struct ds1216_regs regs;

        ds1216_switch_ds_to_clock(priv->ioaddr);
        ds1216_read(priv->ioaddr, (u8 *)&regs);

        regs.tsec = 0; /* clear 0.1 and 0.01 seconds */
        regs.sec = bin2bcd(tm->tm_sec);
        regs.min = bin2bcd(tm->tm_min);
        regs.hour &= DS1216_HOUR_1224;
        if (regs.hour && tm->tm_hour > 12) {
                regs.hour |= DS1216_HOUR_AMPM;
                tm->tm_hour -= 12;
        }
        regs.hour |= bin2bcd(tm->tm_hour);
        regs.wday &= ~7;
        regs.wday |= tm->tm_wday;
        regs.mday = bin2bcd(tm->tm_mday);
        regs.month = bin2bcd(tm->tm_mon);
        regs.year = bin2bcd(tm->tm_year % 100);

        ds1216_switch_ds_to_clock(priv->ioaddr);
        ds1216_write(priv->ioaddr, (u8 *)&regs);
        return 0;
}

static const struct rtc_class_ops ds1216_rtc_ops = {
        .read_time      = ds1216_rtc_read_time,
        .set_time       = ds1216_rtc_set_time,
};

static int __init ds1216_rtc_probe(struct platform_device *pdev)
{
        struct ds1216_priv *priv;
        u8 dummy[8];

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

        platform_set_drvdata(pdev, priv);

        priv->ioaddr = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(priv->ioaddr))
                return PTR_ERR(priv->ioaddr);

        priv->rtc = devm_rtc_device_register(&pdev->dev, "ds1216",
                                        &ds1216_rtc_ops, THIS_MODULE);
        if (IS_ERR(priv->rtc))
                return PTR_ERR(priv->rtc);

        /* dummy read to get clock into a known state */
        ds1216_read(priv->ioaddr, dummy);
        return 0;
}

static struct platform_driver ds1216_rtc_platform_driver = {
        .driver         = {
                .name   = "rtc-ds1216",
        },
};

module_platform_driver_probe(ds1216_rtc_platform_driver, ds1216_rtc_probe);

MODULE_AUTHOR("Thomas Bogendoerfer <tsbogend@alpha.franken.de>");
MODULE_DESCRIPTION("DS1216 RTC driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:rtc-ds1216");