// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Driver for the SGS-Thomson M48T35 Timekeeper RAM chip
 *
 * Copyright (C) 2000 Silicon Graphics, Inc.
 * Written by Ulf Carlsson (ulfc@engr.sgi.com)
 *
 * Copyright (C) 2008 Thomas Bogendoerfer
 *
 * Based on code written by Paul Gortmaker.
 */

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

struct m48t35_rtc {
        u8      pad[0x7ff8];    /* starts at 0x7ff8 */
        u8      control;
        u8      sec;
        u8      min;
        u8      hour;
        u8      day;
        u8      date;
        u8      month;
        u8      year;
};

#define M48T35_RTC_SET          0x80
#define M48T35_RTC_READ         0x40

struct m48t35_priv {
        struct rtc_device *rtc;
        struct m48t35_rtc __iomem *reg;
        size_t size;
        unsigned long baseaddr;
        spinlock_t lock;
};

static int m48t35_read_time(struct device *dev, struct rtc_time *tm)
{
        struct m48t35_priv *priv = dev_get_drvdata(dev);
        u8 control;

        /*
         * Only the values that we read from the RTC are set. We leave
         * tm_wday, tm_yday and tm_isdst untouched. Even though the
         * RTC has RTC_DAY_OF_WEEK, we ignore it, as it is only updated
         * by the RTC when initially set to a non-zero value.
         */
        spin_lock_irq(&priv->lock);
        control = readb(&priv->reg->control);
        writeb(control | M48T35_RTC_READ, &priv->reg->control);
        tm->tm_sec = readb(&priv->reg->sec);
        tm->tm_min = readb(&priv->reg->min);
        tm->tm_hour = readb(&priv->reg->hour);
        tm->tm_mday = readb(&priv->reg->date);
        tm->tm_mon = readb(&priv->reg->month);
        tm->tm_year = readb(&priv->reg->year);
        writeb(control, &priv->reg->control);
        spin_unlock_irq(&priv->lock);

        tm->tm_sec = bcd2bin(tm->tm_sec);
        tm->tm_min = bcd2bin(tm->tm_min);
        tm->tm_hour = bcd2bin(tm->tm_hour);
        tm->tm_mday = bcd2bin(tm->tm_mday);
        tm->tm_mon = bcd2bin(tm->tm_mon);
        tm->tm_year = bcd2bin(tm->tm_year);

        /*
         * Account for differences between how the RTC uses the values
         * and how they are defined in a struct rtc_time;
         */
        tm->tm_year += 70;
        if (tm->tm_year <= 69)
                tm->tm_year += 100;

        tm->tm_mon--;
        return 0;
}

static int m48t35_set_time(struct device *dev, struct rtc_time *tm)
{
        struct m48t35_priv *priv = dev_get_drvdata(dev);
        unsigned char mon, day, hrs, min, sec;
        unsigned int yrs;
        u8 control;

        yrs = tm->tm_year + 1900;
        mon = tm->tm_mon + 1;   /* tm_mon starts at zero */
        day = tm->tm_mday;
        hrs = tm->tm_hour;
        min = tm->tm_min;
        sec = tm->tm_sec;

        if (yrs < 1970)
                return -EINVAL;

        yrs -= 1970;
        if (yrs > 255)    /* They are unsigned */
                return -EINVAL;

        if (yrs > 169)
                return -EINVAL;

        if (yrs >= 100)
                yrs -= 100;

        sec = bin2bcd(sec);
        min = bin2bcd(min);
        hrs = bin2bcd(hrs);
        day = bin2bcd(day);
        mon = bin2bcd(mon);
        yrs = bin2bcd(yrs);

        spin_lock_irq(&priv->lock);
        control = readb(&priv->reg->control);
        writeb(control | M48T35_RTC_SET, &priv->reg->control);
        writeb(yrs, &priv->reg->year);
        writeb(mon, &priv->reg->month);
        writeb(day, &priv->reg->date);
        writeb(hrs, &priv->reg->hour);
        writeb(min, &priv->reg->min);
        writeb(sec, &priv->reg->sec);
        writeb(control, &priv->reg->control);
        spin_unlock_irq(&priv->lock);
        return 0;
}

static const struct rtc_class_ops m48t35_ops = {
        .read_time      = m48t35_read_time,
        .set_time       = m48t35_set_time,
};

static int m48t35_probe(struct platform_device *pdev)
{
        struct resource *res;
        struct m48t35_priv *priv;

        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        if (!res)
                return -ENODEV;
        priv = devm_kzalloc(&pdev->dev, sizeof(struct m48t35_priv), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        priv->size = resource_size(res);
        /*
         * kludge: remove the #ifndef after ioc3 resource
         * conflicts are resolved
         */
#ifndef CONFIG_SGI_IP27
        if (!devm_request_mem_region(&pdev->dev, res->start, priv->size,
                                     pdev->name))
                return -EBUSY;
#endif
        priv->baseaddr = res->start;
        priv->reg = devm_ioremap(&pdev->dev, priv->baseaddr, priv->size);
        if (!priv->reg)
                return -ENOMEM;

        spin_lock_init(&priv->lock);

        platform_set_drvdata(pdev, priv);

        priv->rtc = devm_rtc_device_register(&pdev->dev, "m48t35",
                                  &m48t35_ops, THIS_MODULE);
        return PTR_ERR_OR_ZERO(priv->rtc);
}

static struct platform_driver m48t35_platform_driver = {
        .driver         = {
                .name   = "rtc-m48t35",
        },
        .probe          = m48t35_probe,
};

module_platform_driver(m48t35_platform_driver);

MODULE_AUTHOR("Thomas Bogendoerfer <tsbogend@alpha.franken.de>");
MODULE_DESCRIPTION("M48T35 RTC driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:rtc-m48t35");