/*
 * Blackfin On-Chip Real Time Clock Driver
 *  Supports BF51x/BF52x/BF53[123]/BF53[467]/BF54x
 *
 * Copyright 2004-2010 Analog Devices Inc.
 *
 * Enter bugs at http://blackfin.uclinux.org/
 *
 * Licensed under the GPL-2 or later.
 */

/* The biggest issue we deal with in this driver is that register writes are
 * synced to the RTC frequency of 1Hz.  So if you write to a register and
 * attempt to write again before the first write has completed, the new write
 * is simply discarded.  This can easily be troublesome if userspace disables
 * one event (say periodic) and then right after enables an event (say alarm).
 * Since all events are maintained in the same interrupt mask register, if
 * we wrote to it to disable the first event and then wrote to it again to
 * enable the second event, that second event would not be enabled as the
 * write would be discarded and things quickly fall apart.
 *
 * To keep this delay from significantly degrading performance (we, in theory,
 * would have to sleep for up to 1 second every time we wanted to write a
 * register), we only check the write pending status before we start to issue
 * a new write.  We bank on the idea that it doesn't matter when the sync
 * happens so long as we don't attempt another write before it does.  The only
 * time userspace would take this penalty is when they try and do multiple
 * operations right after another ... but in this case, they need to take the
 * sync penalty, so we should be OK.
 *
 * Also note that the RTC_ISTAT register does not suffer this penalty; its
 * writes to clear status registers complete immediately.
 */

/* It may seem odd that there is no SWCNT code in here (which would be exposed
 * via the periodic interrupt event, or PIE).  Since the Blackfin RTC peripheral
 * runs in units of seconds (N/HZ) but the Linux framework runs in units of HZ
 * (2^N HZ), there is no point in keeping code that only provides 1 HZ PIEs.
 * The same exact behavior can be accomplished by using the update interrupt
 * event (UIE).  Maybe down the line the RTC peripheral will suck less in which
 * case we can re-introduce PIE support.
 */

#include <linux/bcd.h>
#include <linux/completion.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/rtc.h>
#include <linux/seq_file.h>
#include <linux/slab.h>

#include <asm/blackfin.h>

#define dev_dbg_stamp(dev) dev_dbg(dev, "%s:%i: here i am\n", __func__, __LINE__)

struct bfin_rtc {
        struct rtc_device *rtc_dev;
        struct rtc_time rtc_alarm;
        u16 rtc_wrote_regs;
};

/* Bit values for the ISTAT / ICTL registers */
#define RTC_ISTAT_WRITE_COMPLETE  0x8000
#define RTC_ISTAT_WRITE_PENDING   0x4000
#define RTC_ISTAT_ALARM_DAY       0x0040
#define RTC_ISTAT_24HR            0x0020
#define RTC_ISTAT_HOUR            0x0010
#define RTC_ISTAT_MIN             0x0008
#define RTC_ISTAT_SEC             0x0004
#define RTC_ISTAT_ALARM           0x0002
#define RTC_ISTAT_STOPWATCH       0x0001

/* Shift values for RTC_STAT register */
#define DAY_BITS_OFF    17
#define HOUR_BITS_OFF   12
#define MIN_BITS_OFF    6
#define SEC_BITS_OFF    0

/* Some helper functions to convert between the common RTC notion of time
 * and the internal Blackfin notion that is encoded in 32bits.
 */
static inline u32 rtc_time_to_bfin(unsigned long now)
{
        u32 sec  = (now % 60);
        u32 min  = (now % (60 * 60)) / 60;
        u32 hour = (now % (60 * 60 * 24)) / (60 * 60);
        u32 days = (now / (60 * 60 * 24));
        return (sec  << SEC_BITS_OFF) +
               (min  << MIN_BITS_OFF) +
               (hour << HOUR_BITS_OFF) +
               (days << DAY_BITS_OFF);
}
static inline unsigned long rtc_bfin_to_time(u32 rtc_bfin)
{
        return (((rtc_bfin >> SEC_BITS_OFF)  & 0x003F)) +
               (((rtc_bfin >> MIN_BITS_OFF)  & 0x003F) * 60) +
               (((rtc_bfin >> HOUR_BITS_OFF) & 0x001F) * 60 * 60) +
               (((rtc_bfin >> DAY_BITS_OFF)  & 0x7FFF) * 60 * 60 * 24);
}
static inline void rtc_bfin_to_tm(u32 rtc_bfin, struct rtc_time *tm)
{
        rtc_time_to_tm(rtc_bfin_to_time(rtc_bfin), tm);
}

/**
 *      bfin_rtc_sync_pending - make sure pending writes have complete
 *
 * Wait for the previous write to a RTC register to complete.
 * Unfortunately, we can't sleep here as that introduces a race condition when
 * turning on interrupt events.  Consider this:
 *  - process sets alarm
 *  - process enables alarm
 *  - process sleeps while waiting for rtc write to sync
 *  - interrupt fires while process is sleeping
 *  - interrupt acks the event by writing to ISTAT
 *  - interrupt sets the WRITE PENDING bit
 *  - interrupt handler finishes
 *  - process wakes up, sees WRITE PENDING bit set, goes to sleep
 *  - interrupt fires while process is sleeping
 * If anyone can point out the obvious solution here, i'm listening :).  This
 * shouldn't be an issue on an SMP or preempt system as this function should
 * only be called with the rtc lock held.
 *
 * Other options:
 *  - disable PREN so the sync happens at 32.768kHZ ... but this changes the
 *    inc rate for all RTC registers from 1HZ to 32.768kHZ ...
 *  - use the write complete IRQ
 */
/*
static void bfin_rtc_sync_pending_polled(void)
{
        while (!(bfin_read_RTC_ISTAT() & RTC_ISTAT_WRITE_COMPLETE))
                if (!(bfin_read_RTC_ISTAT() & RTC_ISTAT_WRITE_PENDING))
                        break;
        bfin_write_RTC_ISTAT(RTC_ISTAT_WRITE_COMPLETE);
}
*/
static DECLARE_COMPLETION(bfin_write_complete);
static void bfin_rtc_sync_pending(struct device *dev)
{
        dev_dbg_stamp(dev);
        while (bfin_read_RTC_ISTAT() & RTC_ISTAT_WRITE_PENDING)
                wait_for_completion_timeout(&bfin_write_complete, HZ * 5);
        dev_dbg_stamp(dev);
}

/**
 *      bfin_rtc_reset - set RTC to sane/known state
 *
 * Initialize the RTC.  Enable pre-scaler to scale RTC clock
 * to 1Hz and clear interrupt/status registers.
 */
static void bfin_rtc_reset(struct device *dev, u16 rtc_ictl)
{
        struct bfin_rtc *rtc = dev_get_drvdata(dev);
        dev_dbg_stamp(dev);
        bfin_rtc_sync_pending(dev);
        bfin_write_RTC_PREN(0x1);
        bfin_write_RTC_ICTL(rtc_ictl);
        bfin_write_RTC_ALARM(0);
        bfin_write_RTC_ISTAT(0xFFFF);
        rtc->rtc_wrote_regs = 0;
}

/**
 *      bfin_rtc_interrupt - handle interrupt from RTC
 *
 * Since we handle all RTC events here, we have to make sure the requested
 * interrupt is enabled (in RTC_ICTL) as the event status register (RTC_ISTAT)
 * always gets updated regardless of the interrupt being enabled.  So when one
 * even we care about (e.g. stopwatch) goes off, we don't want to turn around
 * and say that other events have happened as well (e.g. second).  We do not
 * have to worry about pending writes to the RTC_ICTL register as interrupts
 * only fire if they are enabled in the RTC_ICTL register.
 */
static irqreturn_t bfin_rtc_interrupt(int irq, void *dev_id)
{
        struct device *dev = dev_id;
        struct bfin_rtc *rtc = dev_get_drvdata(dev);
        unsigned long events = 0;
        bool write_complete = false;
        u16 rtc_istat, rtc_istat_clear, rtc_ictl, bits;

        dev_dbg_stamp(dev);

        rtc_istat = bfin_read_RTC_ISTAT();
        rtc_ictl = bfin_read_RTC_ICTL();
        rtc_istat_clear = 0;

        bits = RTC_ISTAT_WRITE_COMPLETE;
        if (rtc_istat & bits) {
                rtc_istat_clear |= bits;
                write_complete = true;
                complete(&bfin_write_complete);
        }

        bits = (RTC_ISTAT_ALARM | RTC_ISTAT_ALARM_DAY);
        if (rtc_ictl & bits) {
                if (rtc_istat & bits) {
                        rtc_istat_clear |= bits;
                        events |= RTC_AF | RTC_IRQF;
                }
        }

        bits = RTC_ISTAT_SEC;
        if (rtc_ictl & bits) {
                if (rtc_istat & bits) {
                        rtc_istat_clear |= bits;
                        events |= RTC_UF | RTC_IRQF;
                }
        }

        if (events)
                rtc_update_irq(rtc->rtc_dev, 1, events);

        if (write_complete || events) {
                bfin_write_RTC_ISTAT(rtc_istat_clear);
                return IRQ_HANDLED;
        } else
                return IRQ_NONE;
}

static void bfin_rtc_int_set(u16 rtc_int)
{
        bfin_write_RTC_ISTAT(rtc_int);
        bfin_write_RTC_ICTL(bfin_read_RTC_ICTL() | rtc_int);
}
static void bfin_rtc_int_clear(u16 rtc_int)
{
        bfin_write_RTC_ICTL(bfin_read_RTC_ICTL() & rtc_int);
}
static void bfin_rtc_int_set_alarm(struct bfin_rtc *rtc)
{
        /* Blackfin has different bits for whether the alarm is
         * more than 24 hours away.
         */
        bfin_rtc_int_set(rtc->rtc_alarm.tm_yday == -1 ? RTC_ISTAT_ALARM : RTC_ISTAT_ALARM_DAY);
}

static int bfin_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
{
        struct bfin_rtc *rtc = dev_get_drvdata(dev);

        dev_dbg_stamp(dev);
        if (enabled)
                bfin_rtc_int_set_alarm(rtc);
        else
                bfin_rtc_int_clear(~(RTC_ISTAT_ALARM | RTC_ISTAT_ALARM_DAY));

        return 0;
}

static int bfin_rtc_read_time(struct device *dev, struct rtc_time *tm)
{
        struct bfin_rtc *rtc = dev_get_drvdata(dev);

        dev_dbg_stamp(dev);

        if (rtc->rtc_wrote_regs & 0x1)
                bfin_rtc_sync_pending(dev);

        rtc_bfin_to_tm(bfin_read_RTC_STAT(), tm);

        return 0;
}

static int bfin_rtc_set_time(struct device *dev, struct rtc_time *tm)
{
        struct bfin_rtc *rtc = dev_get_drvdata(dev);
        int ret;
        unsigned long now;

        dev_dbg_stamp(dev);

        ret = rtc_tm_to_time(tm, &now);
        if (ret == 0) {
                if (rtc->rtc_wrote_regs & 0x1)
                        bfin_rtc_sync_pending(dev);
                bfin_write_RTC_STAT(rtc_time_to_bfin(now));
                rtc->rtc_wrote_regs = 0x1;
        }

        return ret;
}

static int bfin_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
{
        struct bfin_rtc *rtc = dev_get_drvdata(dev);
        dev_dbg_stamp(dev);
        alrm->time = rtc->rtc_alarm;
        bfin_rtc_sync_pending(dev);
        alrm->enabled = !!(bfin_read_RTC_ICTL() & (RTC_ISTAT_ALARM | RTC_ISTAT_ALARM_DAY));
        return 0;
}

static int bfin_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
{
        struct bfin_rtc *rtc = dev_get_drvdata(dev);
        unsigned long rtc_alarm;

        dev_dbg_stamp(dev);

        if (rtc_tm_to_time(&alrm->time, &rtc_alarm))
                return -EINVAL;

        rtc->rtc_alarm = alrm->time;

        bfin_rtc_sync_pending(dev);
        bfin_write_RTC_ALARM(rtc_time_to_bfin(rtc_alarm));
        if (alrm->enabled)
                bfin_rtc_int_set_alarm(rtc);

        return 0;
}

static int bfin_rtc_proc(struct device *dev, struct seq_file *seq)
{
#define yesno(x) ((x) ? "yes" : "no")
        u16 ictl = bfin_read_RTC_ICTL();
        dev_dbg_stamp(dev);
        seq_printf(seq,
                "alarm_IRQ\t: %s\n"
                "wkalarm_IRQ\t: %s\n"
                "seconds_IRQ\t: %s\n",
                yesno(ictl & RTC_ISTAT_ALARM),
                yesno(ictl & RTC_ISTAT_ALARM_DAY),
                yesno(ictl & RTC_ISTAT_SEC));
        return 0;
#undef yesno
}

static struct rtc_class_ops bfin_rtc_ops = {
        .read_time     = bfin_rtc_read_time,
        .set_time      = bfin_rtc_set_time,
        .read_alarm    = bfin_rtc_read_alarm,
        .set_alarm     = bfin_rtc_set_alarm,
        .proc          = bfin_rtc_proc,
        .alarm_irq_enable = bfin_rtc_alarm_irq_enable,
};

static int bfin_rtc_probe(struct platform_device *pdev)
{
        struct bfin_rtc *rtc;
        struct device *dev = &pdev->dev;
        int ret = 0;
        unsigned long timeout = jiffies + HZ;

        dev_dbg_stamp(dev);

        /* Allocate memory for our RTC struct */
        rtc = devm_kzalloc(dev, sizeof(*rtc), GFP_KERNEL);
        if (unlikely(!rtc))
                return -ENOMEM;
        platform_set_drvdata(pdev, rtc);
        device_init_wakeup(dev, 1);

        /* Register our RTC with the RTC framework */
        rtc->rtc_dev = devm_rtc_device_register(dev, pdev->name, &bfin_rtc_ops,
                                                THIS_MODULE);
        if (unlikely(IS_ERR(rtc->rtc_dev))) {
                ret = PTR_ERR(rtc->rtc_dev);
                goto err;
        }

        /* Grab the IRQ and init the hardware */
        ret = devm_request_irq(dev, IRQ_RTC, bfin_rtc_interrupt, 0,
                                pdev->name, dev);
        if (unlikely(ret))
                goto err;
        /* sometimes the bootloader touched things, but the write complete was not
         * enabled, so let's just do a quick timeout here since the IRQ will not fire ...
         */
        while (bfin_read_RTC_ISTAT() & RTC_ISTAT_WRITE_PENDING)
                if (time_after(jiffies, timeout))
                        break;
        bfin_rtc_reset(dev, RTC_ISTAT_WRITE_COMPLETE);
        bfin_write_RTC_SWCNT(0);

        return 0;

err:
        return ret;
}

static int bfin_rtc_remove(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;

        bfin_rtc_reset(dev, 0);

        return 0;
}

#ifdef CONFIG_PM_SLEEP
static int bfin_rtc_suspend(struct device *dev)
{
        dev_dbg_stamp(dev);

        if (device_may_wakeup(dev)) {
                enable_irq_wake(IRQ_RTC);
                bfin_rtc_sync_pending(dev);
        } else
                bfin_rtc_int_clear(0);

        return 0;
}

static int bfin_rtc_resume(struct device *dev)
{
        dev_dbg_stamp(dev);

        if (device_may_wakeup(dev))
                disable_irq_wake(IRQ_RTC);

        /*
         * Since only some of the RTC bits are maintained externally in the
         * Vbat domain, we need to wait for the RTC MMRs to be synced into
         * the core after waking up.  This happens every RTC 1HZ.  Once that
         * has happened, we can go ahead and re-enable the important write
         * complete interrupt event.
         */
        while (!(bfin_read_RTC_ISTAT() & RTC_ISTAT_SEC))
                continue;
        bfin_rtc_int_set(RTC_ISTAT_WRITE_COMPLETE);

        return 0;
}
#endif

static SIMPLE_DEV_PM_OPS(bfin_rtc_pm_ops, bfin_rtc_suspend, bfin_rtc_resume);

static struct platform_driver bfin_rtc_driver = {
        .driver         = {
                .name   = "rtc-bfin",
                .owner  = THIS_MODULE,
                .pm     = &bfin_rtc_pm_ops,
        },
        .probe          = bfin_rtc_probe,
        .remove         = bfin_rtc_remove,
};

module_platform_driver(bfin_rtc_driver);

MODULE_DESCRIPTION("Blackfin On-Chip Real Time Clock Driver");
MODULE_AUTHOR("Mike Frysinger <vapier@gentoo.org>");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:rtc-bfin");