// SPDX-License-Identifier: GPL-2.0+
/*
 * "RTT as Real Time Clock" driver for AT91SAM9 SoC family
 *
 * (C) 2007 Michel Benoit
 *
 * Based on rtc-at91rm9200.c by Rick Bronson
 */

#include <linux/clk.h>
#include <linux/interrupt.h>
#include <linux/ioctl.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/mfd/syscon.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/regmap.h>
#include <linux/rtc.h>
#include <linux/slab.h>
#include <linux/suspend.h>
#include <linux/time.h>

/*
 * This driver uses two configurable hardware resources that live in the
 * AT91SAM9 backup power domain (intended to be powered at all times)
 * to implement the Real Time Clock interfaces
 *
 *  - A "Real-time Timer" (RTT) counts up in seconds from a base time.
 *    We can't assign the counter value (CRTV) ... but we can reset it.
 *
 *  - One of the "General Purpose Backup Registers" (GPBRs) holds the
 *    base time, normally an offset from the beginning of the POSIX
 *    epoch (1970-Jan-1 00:00:00 UTC).  Some systems also include the
 *    local timezone's offset.
 *
 * The RTC's value is the RTT counter plus that offset.  The RTC's alarm
 * is likewise a base (ALMV) plus that offset.
 *
 * Not all RTTs will be used as RTCs; some systems have multiple RTTs to
 * choose from, or a "real" RTC module.  All systems have multiple GPBR
 * registers available, likewise usable for more than "RTC" support.
 */

#define AT91_RTT_MR             0x00            /* Real-time Mode Register */
#define AT91_RTT_RTPRES         (0xffff << 0)   /* Timer Prescaler Value */
#define AT91_RTT_ALMIEN         BIT(16)         /* Alarm Interrupt Enable */
#define AT91_RTT_RTTINCIEN      BIT(17)         /* Increment Interrupt Enable */
#define AT91_RTT_RTTRST         BIT(18)         /* Timer Restart */

#define AT91_RTT_AR             0x04            /* Real-time Alarm Register */
#define AT91_RTT_ALMV           (0xffffffff)    /* Alarm Value */

#define AT91_RTT_VR             0x08            /* Real-time Value Register */
#define AT91_RTT_CRTV           (0xffffffff)    /* Current Real-time Value */

#define AT91_RTT_SR             0x0c            /* Real-time Status Register */
#define AT91_RTT_ALMS           BIT(0)          /* Alarm Status */
#define AT91_RTT_RTTINC         BIT(1)          /* Timer Increment */

/*
 * We store ALARM_DISABLED in ALMV to record that no alarm is set.
 * It's also the reset value for that field.
 */
#define ALARM_DISABLED  ((u32)~0)

struct sam9_rtc {
        void __iomem            *rtt;
        struct rtc_device       *rtcdev;
        u32                     imr;
        struct regmap           *gpbr;
        unsigned int            gpbr_offset;
        int                     irq;
        struct clk              *sclk;
        bool                    suspended;
        unsigned long           events;
        spinlock_t              lock;
};

#define rtt_readl(rtc, field) \
        readl((rtc)->rtt + AT91_RTT_ ## field)
#define rtt_writel(rtc, field, val) \
        writel((val), (rtc)->rtt + AT91_RTT_ ## field)

static inline unsigned int gpbr_readl(struct sam9_rtc *rtc)
{
        unsigned int val;

        regmap_read(rtc->gpbr, rtc->gpbr_offset, &val);

        return val;
}

static inline void gpbr_writel(struct sam9_rtc *rtc, unsigned int val)
{
        regmap_write(rtc->gpbr, rtc->gpbr_offset, val);
}

/*
 * Read current time and date in RTC
 */
static int at91_rtc_readtime(struct device *dev, struct rtc_time *tm)
{
        struct sam9_rtc *rtc = dev_get_drvdata(dev);
        u32 secs, secs2;
        u32 offset;

        /* read current time offset */
        offset = gpbr_readl(rtc);
        if (offset == 0)
                return -EILSEQ;

        /* reread the counter to help sync the two clock domains */
        secs = rtt_readl(rtc, VR);
        secs2 = rtt_readl(rtc, VR);
        if (secs != secs2)
                secs = rtt_readl(rtc, VR);

        rtc_time64_to_tm(offset + secs, tm);

        dev_dbg(dev, "%s: %ptR\n", __func__, tm);

        return 0;
}

/*
 * Set current time and date in RTC
 */
static int at91_rtc_settime(struct device *dev, struct rtc_time *tm)
{
        struct sam9_rtc *rtc = dev_get_drvdata(dev);
        u32 offset, alarm, mr;
        unsigned long secs;

        dev_dbg(dev, "%s: %ptR\n", __func__, tm);

        secs = rtc_tm_to_time64(tm);

        mr = rtt_readl(rtc, MR);

        /* disable interrupts */
        rtt_writel(rtc, MR, mr & ~(AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN));

        /* read current time offset */
        offset = gpbr_readl(rtc);

        /* store the new base time in a battery backup register */
        secs += 1;
        gpbr_writel(rtc, secs);

        /* adjust the alarm time for the new base */
        alarm = rtt_readl(rtc, AR);
        if (alarm != ALARM_DISABLED) {
                if (offset > secs) {
                        /* time jumped backwards, increase time until alarm */
                        alarm += (offset - secs);
                } else if ((alarm + offset) > secs) {
                        /* time jumped forwards, decrease time until alarm */
                        alarm -= (secs - offset);
                } else {
                        /* time jumped past the alarm, disable alarm */
                        alarm = ALARM_DISABLED;
                        mr &= ~AT91_RTT_ALMIEN;
                }
                rtt_writel(rtc, AR, alarm);
        }

        /* reset the timer, and re-enable interrupts */
        rtt_writel(rtc, MR, mr | AT91_RTT_RTTRST);

        return 0;
}

static int at91_rtc_readalarm(struct device *dev, struct rtc_wkalrm *alrm)
{
        struct sam9_rtc *rtc = dev_get_drvdata(dev);
        struct rtc_time *tm = &alrm->time;
        u32 alarm = rtt_readl(rtc, AR);
        u32 offset;

        offset = gpbr_readl(rtc);
        if (offset == 0)
                return -EILSEQ;

        memset(alrm, 0, sizeof(*alrm));
        if (alarm != ALARM_DISABLED) {
                rtc_time64_to_tm(offset + alarm, tm);

                dev_dbg(dev, "%s: %ptR\n", __func__, tm);

                if (rtt_readl(rtc, MR) & AT91_RTT_ALMIEN)
                        alrm->enabled = 1;
        }

        return 0;
}

static int at91_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
{
        struct sam9_rtc *rtc = dev_get_drvdata(dev);
        struct rtc_time *tm = &alrm->time;
        unsigned long secs;
        u32 offset;
        u32 mr;

        secs = rtc_tm_to_time64(tm);

        offset = gpbr_readl(rtc);
        if (offset == 0) {
                /* time is not set */
                return -EILSEQ;
        }
        mr = rtt_readl(rtc, MR);
        rtt_writel(rtc, MR, mr & ~AT91_RTT_ALMIEN);

        /* alarm in the past? finish and leave disabled */
        if (secs <= offset) {
                rtt_writel(rtc, AR, ALARM_DISABLED);
                return 0;
        }

        /* else set alarm and maybe enable it */
        rtt_writel(rtc, AR, secs - offset);
        if (alrm->enabled)
                rtt_writel(rtc, MR, mr | AT91_RTT_ALMIEN);

        dev_dbg(dev, "%s: %ptR\n", __func__, tm);

        return 0;
}

static int at91_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
{
        struct sam9_rtc *rtc = dev_get_drvdata(dev);
        u32 mr = rtt_readl(rtc, MR);

        dev_dbg(dev, "alarm_irq_enable: enabled=%08x, mr %08x\n", enabled, mr);
        if (enabled)
                rtt_writel(rtc, MR, mr | AT91_RTT_ALMIEN);
        else
                rtt_writel(rtc, MR, mr & ~AT91_RTT_ALMIEN);
        return 0;
}

/*
 * Provide additional RTC information in /proc/driver/rtc
 */
static int at91_rtc_proc(struct device *dev, struct seq_file *seq)
{
        struct sam9_rtc *rtc = dev_get_drvdata(dev);
        u32 mr = rtt_readl(rtc, MR);

        seq_printf(seq, "update_IRQ\t: %s\n",
                   (mr & AT91_RTT_RTTINCIEN) ? "yes" : "no");
        return 0;
}

static irqreturn_t at91_rtc_cache_events(struct sam9_rtc *rtc)
{
        u32 sr, mr;

        /* Shared interrupt may be for another device.  Note: reading
         * SR clears it, so we must only read it in this irq handler!
         */
        mr = rtt_readl(rtc, MR) & (AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN);
        sr = rtt_readl(rtc, SR) & (mr >> 16);
        if (!sr)
                return IRQ_NONE;

        /* alarm status */
        if (sr & AT91_RTT_ALMS)
                rtc->events |= (RTC_AF | RTC_IRQF);

        /* timer update/increment */
        if (sr & AT91_RTT_RTTINC)
                rtc->events |= (RTC_UF | RTC_IRQF);

        return IRQ_HANDLED;
}

static void at91_rtc_flush_events(struct sam9_rtc *rtc)
{
        if (!rtc->events)
                return;

        rtc_update_irq(rtc->rtcdev, 1, rtc->events);
        rtc->events = 0;

        pr_debug("%s: num=%ld, events=0x%02lx\n", __func__,
                 rtc->events >> 8, rtc->events & 0x000000FF);
}

/*
 * IRQ handler for the RTC
 */
static irqreturn_t at91_rtc_interrupt(int irq, void *_rtc)
{
        struct sam9_rtc *rtc = _rtc;
        int ret;

        spin_lock(&rtc->lock);

        ret = at91_rtc_cache_events(rtc);

        /* We're called in suspended state */
        if (rtc->suspended) {
                /* Mask irqs coming from this peripheral */
                rtt_writel(rtc, MR,
                           rtt_readl(rtc, MR) &
                           ~(AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN));
                /* Trigger a system wakeup */
                pm_system_wakeup();
        } else {
                at91_rtc_flush_events(rtc);
        }

        spin_unlock(&rtc->lock);

        return ret;
}

static const struct rtc_class_ops at91_rtc_ops = {
        .read_time      = at91_rtc_readtime,
        .set_time       = at91_rtc_settime,
        .read_alarm     = at91_rtc_readalarm,
        .set_alarm      = at91_rtc_setalarm,
        .proc           = at91_rtc_proc,
        .alarm_irq_enable = at91_rtc_alarm_irq_enable,
};

/*
 * Initialize and install RTC driver
 */
static int at91_rtc_probe(struct platform_device *pdev)
{
        struct sam9_rtc *rtc;
        int             ret, irq;
        u32             mr;
        unsigned int    sclk_rate;
        struct of_phandle_args args;

        irq = platform_get_irq(pdev, 0);
        if (irq < 0)
                return irq;

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

        spin_lock_init(&rtc->lock);
        rtc->irq = irq;

        /* platform setup code should have handled this; sigh */
        if (!device_can_wakeup(&pdev->dev))
                device_init_wakeup(&pdev->dev, true);

        platform_set_drvdata(pdev, rtc);

        rtc->rtt = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(rtc->rtt))
                return PTR_ERR(rtc->rtt);

        ret = of_parse_phandle_with_fixed_args(pdev->dev.of_node,
                                               "atmel,rtt-rtc-time-reg", 1, 0,
                                               &args);
        if (ret)
                return ret;

        rtc->gpbr = syscon_node_to_regmap(args.np);
        of_node_put(args.np);
        rtc->gpbr_offset = args.args[0];
        if (IS_ERR(rtc->gpbr)) {
                dev_err(&pdev->dev, "failed to retrieve gpbr regmap, aborting.\n");
                return -ENOMEM;
        }

        rtc->sclk = devm_clk_get(&pdev->dev, NULL);
        if (IS_ERR(rtc->sclk))
                return PTR_ERR(rtc->sclk);

        ret = clk_prepare_enable(rtc->sclk);
        if (ret) {
                dev_err(&pdev->dev, "Could not enable slow clock\n");
                return ret;
        }

        sclk_rate = clk_get_rate(rtc->sclk);
        if (!sclk_rate || sclk_rate > AT91_RTT_RTPRES) {
                dev_err(&pdev->dev, "Invalid slow clock rate\n");
                ret = -EINVAL;
                goto err_clk;
        }

        mr = rtt_readl(rtc, MR);

        /* unless RTT is counting at 1 Hz, re-initialize it */
        if ((mr & AT91_RTT_RTPRES) != sclk_rate) {
                mr = AT91_RTT_RTTRST | (sclk_rate & AT91_RTT_RTPRES);
                gpbr_writel(rtc, 0);
        }

        /* disable all interrupts (same as on shutdown path) */
        mr &= ~(AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN);
        rtt_writel(rtc, MR, mr);

        rtc->rtcdev = devm_rtc_allocate_device(&pdev->dev);
        if (IS_ERR(rtc->rtcdev)) {
                ret = PTR_ERR(rtc->rtcdev);
                goto err_clk;
        }

        rtc->rtcdev->ops = &at91_rtc_ops;
        rtc->rtcdev->range_max = U32_MAX;

        /* register irq handler after we know what name we'll use */
        ret = devm_request_irq(&pdev->dev, rtc->irq, at91_rtc_interrupt,
                               IRQF_SHARED | IRQF_COND_SUSPEND,
                               dev_name(&rtc->rtcdev->dev), rtc);
        if (ret) {
                dev_dbg(&pdev->dev, "can't share IRQ %d?\n", rtc->irq);
                goto err_clk;
        }

        /* NOTE:  sam9260 rev A silicon has a ROM bug which resets the
         * RTT on at least some reboots.  If you have that chip, you must
         * initialize the time from some external source like a GPS, wall
         * clock, discrete RTC, etc
         */

        if (gpbr_readl(rtc) == 0)
                dev_warn(&pdev->dev, "%s: SET TIME!\n",
                         dev_name(&rtc->rtcdev->dev));

        return devm_rtc_register_device(rtc->rtcdev);

err_clk:
        clk_disable_unprepare(rtc->sclk);

        return ret;
}

/*
 * Disable and remove the RTC driver
 */
static void at91_rtc_remove(struct platform_device *pdev)
{
        struct sam9_rtc *rtc = platform_get_drvdata(pdev);
        u32             mr = rtt_readl(rtc, MR);

        /* disable all interrupts */
        rtt_writel(rtc, MR, mr & ~(AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN));

        clk_disable_unprepare(rtc->sclk);
}

static void at91_rtc_shutdown(struct platform_device *pdev)
{
        struct sam9_rtc *rtc = platform_get_drvdata(pdev);
        u32             mr = rtt_readl(rtc, MR);

        rtc->imr = mr & (AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN);
        rtt_writel(rtc, MR, mr & ~rtc->imr);
}

#ifdef CONFIG_PM_SLEEP

/* AT91SAM9 RTC Power management control */

static int at91_rtc_suspend(struct device *dev)
{
        struct sam9_rtc *rtc = dev_get_drvdata(dev);
        u32             mr = rtt_readl(rtc, MR);

        /*
         * This IRQ is shared with DBGU and other hardware which isn't
         * necessarily a wakeup event source.
         */
        rtc->imr = mr & (AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN);
        if (rtc->imr) {
                if (device_may_wakeup(dev) && (mr & AT91_RTT_ALMIEN)) {
                        unsigned long flags;

                        enable_irq_wake(rtc->irq);
                        spin_lock_irqsave(&rtc->lock, flags);
                        rtc->suspended = true;
                        spin_unlock_irqrestore(&rtc->lock, flags);
                        /* don't let RTTINC cause wakeups */
                        if (mr & AT91_RTT_RTTINCIEN)
                                rtt_writel(rtc, MR, mr & ~AT91_RTT_RTTINCIEN);
                } else {
                        rtt_writel(rtc, MR, mr & ~rtc->imr);
                }
        }

        return 0;
}

static int at91_rtc_resume(struct device *dev)
{
        struct sam9_rtc *rtc = dev_get_drvdata(dev);
        u32             mr;

        if (rtc->imr) {
                unsigned long flags;

                if (device_may_wakeup(dev))
                        disable_irq_wake(rtc->irq);
                mr = rtt_readl(rtc, MR);
                rtt_writel(rtc, MR, mr | rtc->imr);

                spin_lock_irqsave(&rtc->lock, flags);
                rtc->suspended = false;
                at91_rtc_cache_events(rtc);
                at91_rtc_flush_events(rtc);
                spin_unlock_irqrestore(&rtc->lock, flags);
        }

        return 0;
}
#endif

static SIMPLE_DEV_PM_OPS(at91_rtc_pm_ops, at91_rtc_suspend, at91_rtc_resume);

static const struct of_device_id at91_rtc_dt_ids[] = {
        { .compatible = "atmel,at91sam9260-rtt" },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, at91_rtc_dt_ids);

static struct platform_driver at91_rtc_driver = {
        .probe          = at91_rtc_probe,
        .remove         = at91_rtc_remove,
        .shutdown       = at91_rtc_shutdown,
        .driver         = {
                .name   = "rtc-at91sam9",
                .pm     = &at91_rtc_pm_ops,
                .of_match_table = at91_rtc_dt_ids,
        },
};

module_platform_driver(at91_rtc_driver);

MODULE_AUTHOR("Michel Benoit");
MODULE_DESCRIPTION("RTC driver for Atmel AT91SAM9x");
MODULE_LICENSE("GPL");