// SPDX-License-Identifier: GPL-2.0-only
/*
 * rtc-ds1305.c -- driver for DS1305 and DS1306 SPI RTC chips
 *
 * Copyright (C) 2008 David Brownell
 */
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/bcd.h>
#include <linux/slab.h>
#include <linux/rtc.h>
#include <linux/workqueue.h>

#include <linux/spi/spi.h>
#include <linux/spi/ds1305.h>
#include <linux/module.h>


/*
 * Registers ... mask DS1305_WRITE into register address to write,
 * otherwise you're reading it.  All non-bitmask values are BCD.
 */
#define DS1305_WRITE            0x80


/* RTC date/time ... the main special cases are that we:
 *  - Need fancy "hours" encoding in 12hour mode
 *  - Don't rely on the "day-of-week" field (or tm_wday)
 *  - Are a 21st-century clock (2000 <= year < 2100)
 */
#define DS1305_RTC_LEN          7               /* bytes for RTC regs */

#define DS1305_SEC              0x00            /* register addresses */
#define DS1305_MIN              0x01
#define DS1305_HOUR             0x02
#       define DS1305_HR_12             0x40    /* set == 12 hr mode */
#       define DS1305_HR_PM             0x20    /* set == PM (12hr mode) */
#define DS1305_WDAY             0x03
#define DS1305_MDAY             0x04
#define DS1305_MON              0x05
#define DS1305_YEAR             0x06


/* The two alarms have only sec/min/hour/wday fields (ALM_LEN).
 * DS1305_ALM_DISABLE disables a match field (some combos are bad).
 *
 * NOTE that since we don't use WDAY, we limit ourselves to alarms
 * only one day into the future (vs potentially up to a week).
 *
 * NOTE ALSO that while we could generate once-a-second IRQs (UIE), we
 * don't currently support them.  We'd either need to do it only when
 * no alarm is pending (not the standard model), or to use the second
 * alarm (implying that this is a DS1305 not DS1306, *and* that either
 * it's wired up a second IRQ we know, or that INTCN is set)
 */
#define DS1305_ALM_LEN          4               /* bytes for ALM regs */
#define DS1305_ALM_DISABLE      0x80

#define DS1305_ALM0(r)          (0x07 + (r))    /* register addresses */
#define DS1305_ALM1(r)          (0x0b + (r))


/* three control registers */
#define DS1305_CONTROL_LEN      3               /* bytes of control regs */

#define DS1305_CONTROL          0x0f            /* register addresses */
#       define DS1305_nEOSC             0x80    /* low enables oscillator */
#       define DS1305_WP                0x40    /* write protect */
#       define DS1305_INTCN             0x04    /* clear == only int0 used */
#       define DS1306_1HZ               0x04    /* enable 1Hz output */
#       define DS1305_AEI1              0x02    /* enable ALM1 IRQ */
#       define DS1305_AEI0              0x01    /* enable ALM0 IRQ */
#define DS1305_STATUS           0x10
/* status has just AEIx bits, mirrored as IRQFx */
#define DS1305_TRICKLE          0x11
/* trickle bits are defined in <linux/spi/ds1305.h> */

/* a bunch of NVRAM */
#define DS1305_NVRAM_LEN        96              /* bytes of NVRAM */

#define DS1305_NVRAM            0x20            /* register addresses */


struct ds1305 {
        struct spi_device       *spi;
        struct rtc_device       *rtc;

        struct work_struct      work;

        unsigned long           flags;
#define FLAG_EXITING    0

        bool                    hr12;
        u8                      ctrl[DS1305_CONTROL_LEN];
};


/*----------------------------------------------------------------------*/

/*
 * Utilities ...  tolerate 12-hour AM/PM notation in case of non-Linux
 * software (like a bootloader) which may require it.
 */

static unsigned bcd2hour(u8 bcd)
{
        if (bcd & DS1305_HR_12) {
                unsigned        hour = 0;

                bcd &= ~DS1305_HR_12;
                if (bcd & DS1305_HR_PM) {
                        hour = 12;
                        bcd &= ~DS1305_HR_PM;
                }
                hour += bcd2bin(bcd);
                return hour - 1;
        }
        return bcd2bin(bcd);
}

static u8 hour2bcd(bool hr12, int hour)
{
        if (hr12) {
                hour++;
                if (hour <= 12)
                        return DS1305_HR_12 | bin2bcd(hour);
                hour -= 12;
                return DS1305_HR_12 | DS1305_HR_PM | bin2bcd(hour);
        }
        return bin2bcd(hour);
}

/*----------------------------------------------------------------------*/

/*
 * Interface to RTC framework
 */

static int ds1305_alarm_irq_enable(struct device *dev, unsigned int enabled)
{
        struct ds1305   *ds1305 = dev_get_drvdata(dev);
        u8              buf[2];
        long            err = -EINVAL;

        buf[0] = DS1305_WRITE | DS1305_CONTROL;
        buf[1] = ds1305->ctrl[0];

        if (enabled) {
                if (ds1305->ctrl[0] & DS1305_AEI0)
                        goto done;
                buf[1] |= DS1305_AEI0;
        } else {
                if (!(buf[1] & DS1305_AEI0))
                        goto done;
                buf[1] &= ~DS1305_AEI0;
        }
        err = spi_write_then_read(ds1305->spi, buf, sizeof(buf), NULL, 0);
        if (err >= 0)
                ds1305->ctrl[0] = buf[1];
done:
        return err;

}


/*
 * Get/set of date and time is pretty normal.
 */

static int ds1305_get_time(struct device *dev, struct rtc_time *time)
{
        struct ds1305   *ds1305 = dev_get_drvdata(dev);
        u8              addr = DS1305_SEC;
        u8              buf[DS1305_RTC_LEN];
        int             status;

        /* Use write-then-read to get all the date/time registers
         * since dma from stack is nonportable
         */
        status = spi_write_then_read(ds1305->spi, &addr, sizeof(addr),
                        buf, sizeof(buf));
        if (status < 0)
                return status;

        dev_vdbg(dev, "%s: %3ph, %4ph\n", "read", &buf[0], &buf[3]);

        /* Decode the registers */
        time->tm_sec = bcd2bin(buf[DS1305_SEC]);
        time->tm_min = bcd2bin(buf[DS1305_MIN]);
        time->tm_hour = bcd2hour(buf[DS1305_HOUR]);
        time->tm_wday = buf[DS1305_WDAY] - 1;
        time->tm_mday = bcd2bin(buf[DS1305_MDAY]);
        time->tm_mon = bcd2bin(buf[DS1305_MON]) - 1;
        time->tm_year = bcd2bin(buf[DS1305_YEAR]) + 100;

        dev_vdbg(dev, "%s secs=%d, mins=%d, "
                "hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
                "read", time->tm_sec, time->tm_min,
                time->tm_hour, time->tm_mday,
                time->tm_mon, time->tm_year, time->tm_wday);

        return 0;
}

static int ds1305_set_time(struct device *dev, struct rtc_time *time)
{
        struct ds1305   *ds1305 = dev_get_drvdata(dev);
        u8              buf[1 + DS1305_RTC_LEN];
        u8              *bp = buf;

        dev_vdbg(dev, "%s secs=%d, mins=%d, "
                "hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
                "write", time->tm_sec, time->tm_min,
                time->tm_hour, time->tm_mday,
                time->tm_mon, time->tm_year, time->tm_wday);

        /* Write registers starting at the first time/date address. */
        *bp++ = DS1305_WRITE | DS1305_SEC;

        *bp++ = bin2bcd(time->tm_sec);
        *bp++ = bin2bcd(time->tm_min);
        *bp++ = hour2bcd(ds1305->hr12, time->tm_hour);
        *bp++ = (time->tm_wday < 7) ? (time->tm_wday + 1) : 1;
        *bp++ = bin2bcd(time->tm_mday);
        *bp++ = bin2bcd(time->tm_mon + 1);
        *bp++ = bin2bcd(time->tm_year - 100);

        dev_dbg(dev, "%s: %3ph, %4ph\n", "write", &buf[1], &buf[4]);

        /* use write-then-read since dma from stack is nonportable */
        return spi_write_then_read(ds1305->spi, buf, sizeof(buf),
                        NULL, 0);
}

/*
 * Get/set of alarm is a bit funky:
 *
 * - First there's the inherent raciness of getting the (partitioned)
 *   status of an alarm that could trigger while we're reading parts
 *   of that status.
 *
 * - Second there's its limited range (we could increase it a bit by
 *   relying on WDAY), which means it will easily roll over.
 *
 * - Third there's the choice of two alarms and alarm signals.
 *   Here we use ALM0 and expect that nINT0 (open drain) is used;
 *   that's the only real option for DS1306 runtime alarms, and is
 *   natural on DS1305.
 *
 * - Fourth, there's also ALM1, and a second interrupt signal:
 *     + On DS1305 ALM1 uses nINT1 (when INTCN=1) else nINT0;
 *     + On DS1306 ALM1 only uses INT1 (an active high pulse)
 *       and it won't work when VCC1 is active.
 *
 *   So to be most general, we should probably set both alarms to the
 *   same value, letting ALM1 be the wakeup event source on DS1306
 *   and handling several wiring options on DS1305.
 *
 * - Fifth, we support the polled mode (as well as possible; why not?)
 *   even when no interrupt line is wired to an IRQ.
 */

/*
 * Context: caller holds rtc->ops_lock (to protect ds1305->ctrl)
 */
static int ds1305_get_alarm(struct device *dev, struct rtc_wkalrm *alm)
{
        struct ds1305   *ds1305 = dev_get_drvdata(dev);
        struct spi_device *spi = ds1305->spi;
        u8              addr;
        int             status;
        u8              buf[DS1305_ALM_LEN];

        /* Refresh control register cache BEFORE reading ALM0 registers,
         * since reading alarm registers acks any pending IRQ.  That
         * makes returning "pending" status a bit of a lie, but that bit
         * of EFI status is at best fragile anyway (given IRQ handlers).
         */
        addr = DS1305_CONTROL;
        status = spi_write_then_read(spi, &addr, sizeof(addr),
                        ds1305->ctrl, sizeof(ds1305->ctrl));
        if (status < 0)
                return status;

        alm->enabled = !!(ds1305->ctrl[0] & DS1305_AEI0);
        alm->pending = !!(ds1305->ctrl[1] & DS1305_AEI0);

        /* get and check ALM0 registers */
        addr = DS1305_ALM0(DS1305_SEC);
        status = spi_write_then_read(spi, &addr, sizeof(addr),
                        buf, sizeof(buf));
        if (status < 0)
                return status;

        dev_vdbg(dev, "%s: %02x %02x %02x %02x\n",
                "alm0 read", buf[DS1305_SEC], buf[DS1305_MIN],
                buf[DS1305_HOUR], buf[DS1305_WDAY]);

        if ((DS1305_ALM_DISABLE & buf[DS1305_SEC])
                        || (DS1305_ALM_DISABLE & buf[DS1305_MIN])
                        || (DS1305_ALM_DISABLE & buf[DS1305_HOUR]))
                return -EIO;

        /* Stuff these values into alm->time and let RTC framework code
         * fill in the rest ... and also handle rollover to tomorrow when
         * that's needed.
         */
        alm->time.tm_sec = bcd2bin(buf[DS1305_SEC]);
        alm->time.tm_min = bcd2bin(buf[DS1305_MIN]);
        alm->time.tm_hour = bcd2hour(buf[DS1305_HOUR]);

        return 0;
}

/*
 * Context: caller holds rtc->ops_lock (to protect ds1305->ctrl)
 */
static int ds1305_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
{
        struct ds1305   *ds1305 = dev_get_drvdata(dev);
        struct spi_device *spi = ds1305->spi;
        unsigned long   now, later;
        struct rtc_time tm;
        int             status;
        u8              buf[1 + DS1305_ALM_LEN];

        /* convert desired alarm to time_t */
        later = rtc_tm_to_time64(&alm->time);

        /* Read current time as time_t */
        status = ds1305_get_time(dev, &tm);
        if (status < 0)
                return status;
        now = rtc_tm_to_time64(&tm);

        /* make sure alarm fires within the next 24 hours */
        if (later <= now)
                return -EINVAL;
        if ((later - now) > 24 * 60 * 60)
                return -EDOM;

        /* disable alarm if needed */
        if (ds1305->ctrl[0] & DS1305_AEI0) {
                ds1305->ctrl[0] &= ~DS1305_AEI0;

                buf[0] = DS1305_WRITE | DS1305_CONTROL;
                buf[1] = ds1305->ctrl[0];
                status = spi_write_then_read(ds1305->spi, buf, 2, NULL, 0);
                if (status < 0)
                        return status;
        }

        /* write alarm */
        buf[0] = DS1305_WRITE | DS1305_ALM0(DS1305_SEC);
        buf[1 + DS1305_SEC] = bin2bcd(alm->time.tm_sec);
        buf[1 + DS1305_MIN] = bin2bcd(alm->time.tm_min);
        buf[1 + DS1305_HOUR] = hour2bcd(ds1305->hr12, alm->time.tm_hour);
        buf[1 + DS1305_WDAY] = DS1305_ALM_DISABLE;

        dev_dbg(dev, "%s: %02x %02x %02x %02x\n",
                "alm0 write", buf[1 + DS1305_SEC], buf[1 + DS1305_MIN],
                buf[1 + DS1305_HOUR], buf[1 + DS1305_WDAY]);

        status = spi_write_then_read(spi, buf, sizeof(buf), NULL, 0);
        if (status < 0)
                return status;

        /* enable alarm if requested */
        if (alm->enabled) {
                ds1305->ctrl[0] |= DS1305_AEI0;

                buf[0] = DS1305_WRITE | DS1305_CONTROL;
                buf[1] = ds1305->ctrl[0];
                status = spi_write_then_read(ds1305->spi, buf, 2, NULL, 0);
        }

        return status;
}

#ifdef CONFIG_PROC_FS

static int ds1305_proc(struct device *dev, struct seq_file *seq)
{
        struct ds1305   *ds1305 = dev_get_drvdata(dev);
        char            *diodes = "no";
        char            *resistors = "";

        /* ctrl[2] is treated as read-only; no locking needed */
        if ((ds1305->ctrl[2] & 0xf0) == DS1305_TRICKLE_MAGIC) {
                switch (ds1305->ctrl[2] & 0x0c) {
                case DS1305_TRICKLE_DS2:
                        diodes = "2 diodes, ";
                        break;
                case DS1305_TRICKLE_DS1:
                        diodes = "1 diode, ";
                        break;
                default:
                        goto done;
                }
                switch (ds1305->ctrl[2] & 0x03) {
                case DS1305_TRICKLE_2K:
                        resistors = "2k Ohm";
                        break;
                case DS1305_TRICKLE_4K:
                        resistors = "4k Ohm";
                        break;
                case DS1305_TRICKLE_8K:
                        resistors = "8k Ohm";
                        break;
                default:
                        diodes = "no";
                        break;
                }
        }

done:
        seq_printf(seq, "trickle_charge\t: %s%s\n", diodes, resistors);

        return 0;
}

#else
#define ds1305_proc     NULL
#endif

static const struct rtc_class_ops ds1305_ops = {
        .read_time      = ds1305_get_time,
        .set_time       = ds1305_set_time,
        .read_alarm     = ds1305_get_alarm,
        .set_alarm      = ds1305_set_alarm,
        .proc           = ds1305_proc,
        .alarm_irq_enable = ds1305_alarm_irq_enable,
};

static void ds1305_work(struct work_struct *work)
{
        struct ds1305   *ds1305 = container_of(work, struct ds1305, work);
        struct mutex    *lock = &ds1305->rtc->ops_lock;
        struct spi_device *spi = ds1305->spi;
        u8              buf[3];
        int             status;

        /* lock to protect ds1305->ctrl */
        mutex_lock(lock);

        /* Disable the IRQ, and clear its status ... for now, we "know"
         * that if more than one alarm is active, they're in sync.
         * Note that reading ALM data registers also clears IRQ status.
         */
        ds1305->ctrl[0] &= ~(DS1305_AEI1 | DS1305_AEI0);
        ds1305->ctrl[1] = 0;

        buf[0] = DS1305_WRITE | DS1305_CONTROL;
        buf[1] = ds1305->ctrl[0];
        buf[2] = 0;

        status = spi_write_then_read(spi, buf, sizeof(buf),
                        NULL, 0);
        if (status < 0)
                dev_dbg(&spi->dev, "clear irq --> %d\n", status);

        mutex_unlock(lock);

        if (!test_bit(FLAG_EXITING, &ds1305->flags))
                enable_irq(spi->irq);

        rtc_update_irq(ds1305->rtc, 1, RTC_AF | RTC_IRQF);
}

/*
 * This "real" IRQ handler hands off to a workqueue mostly to allow
 * mutex locking for ds1305->ctrl ... unlike I2C, we could issue async
 * I/O requests in IRQ context (to clear the IRQ status).
 */
static irqreturn_t ds1305_irq(int irq, void *p)
{
        struct ds1305           *ds1305 = p;

        disable_irq(irq);
        schedule_work(&ds1305->work);
        return IRQ_HANDLED;
}

/*----------------------------------------------------------------------*/

/*
 * Interface for NVRAM
 */

static void msg_init(struct spi_message *m, struct spi_transfer *x,
                u8 *addr, size_t count, char *tx, char *rx)
{
        spi_message_init(m);
        memset(x, 0, 2 * sizeof(*x));

        x->tx_buf = addr;
        x->len = 1;
        spi_message_add_tail(x, m);

        x++;

        x->tx_buf = tx;
        x->rx_buf = rx;
        x->len = count;
        spi_message_add_tail(x, m);
}

static int ds1305_nvram_read(void *priv, unsigned int off, void *buf,
                             size_t count)
{
        struct ds1305           *ds1305 = priv;
        struct spi_device       *spi = ds1305->spi;
        u8                      addr;
        struct spi_message      m;
        struct spi_transfer     x[2];

        addr = DS1305_NVRAM + off;
        msg_init(&m, x, &addr, count, NULL, buf);

        return spi_sync(spi, &m);
}

static int ds1305_nvram_write(void *priv, unsigned int off, void *buf,
                              size_t count)
{
        struct ds1305           *ds1305 = priv;
        struct spi_device       *spi = ds1305->spi;
        u8                      addr;
        struct spi_message      m;
        struct spi_transfer     x[2];

        addr = (DS1305_WRITE | DS1305_NVRAM) + off;
        msg_init(&m, x, &addr, count, buf, NULL);

        return spi_sync(spi, &m);
}

/*----------------------------------------------------------------------*/

/*
 * Interface to SPI stack
 */

static int ds1305_probe(struct spi_device *spi)
{
        struct ds1305                   *ds1305;
        int                             status;
        u8                              addr, value;
        struct ds1305_platform_data     *pdata = dev_get_platdata(&spi->dev);
        bool                            write_ctrl = false;
        struct nvmem_config ds1305_nvmem_cfg = {
                .name = "ds1305_nvram",
                .word_size = 1,
                .stride = 1,
                .size = DS1305_NVRAM_LEN,
                .reg_read = ds1305_nvram_read,
                .reg_write = ds1305_nvram_write,
        };

        /* Sanity check board setup data.  This may be hooked up
         * in 3wire mode, but we don't care.  Note that unless
         * there's an inverter in place, this needs SPI_CS_HIGH!
         */
        if ((spi->bits_per_word && spi->bits_per_word != 8)
                        || (spi->max_speed_hz > 2000000)
                        || !(spi->mode & SPI_CPHA))
                return -EINVAL;

        /* set up driver data */
        ds1305 = devm_kzalloc(&spi->dev, sizeof(*ds1305), GFP_KERNEL);
        if (!ds1305)
                return -ENOMEM;
        ds1305->spi = spi;
        spi_set_drvdata(spi, ds1305);

        /* read and cache control registers */
        addr = DS1305_CONTROL;
        status = spi_write_then_read(spi, &addr, sizeof(addr),
                        ds1305->ctrl, sizeof(ds1305->ctrl));
        if (status < 0) {
                dev_dbg(&spi->dev, "can't %s, %d\n",
                                "read", status);
                return status;
        }

        dev_dbg(&spi->dev, "ctrl %s: %3ph\n", "read", ds1305->ctrl);

        /* Sanity check register values ... partially compensating for the
         * fact that SPI has no device handshake.  A pullup on MISO would
         * make these tests fail; but not all systems will have one.  If
         * some register is neither 0x00 nor 0xff, a chip is likely there.
         */
        if ((ds1305->ctrl[0] & 0x38) != 0 || (ds1305->ctrl[1] & 0xfc) != 0) {
                dev_dbg(&spi->dev, "RTC chip is not present\n");
                return -ENODEV;
        }
        if (ds1305->ctrl[2] == 0)
                dev_dbg(&spi->dev, "chip may not be present\n");

        /* enable writes if needed ... if we were paranoid it would
         * make sense to enable them only when absolutely necessary.
         */
        if (ds1305->ctrl[0] & DS1305_WP) {
                u8              buf[2];

                ds1305->ctrl[0] &= ~DS1305_WP;

                buf[0] = DS1305_WRITE | DS1305_CONTROL;
                buf[1] = ds1305->ctrl[0];
                status = spi_write_then_read(spi, buf, sizeof(buf), NULL, 0);

                dev_dbg(&spi->dev, "clear WP --> %d\n", status);
                if (status < 0)
                        return status;
        }

        /* on DS1305, maybe start oscillator; like most low power
         * oscillators, it may take a second to stabilize
         */
        if (ds1305->ctrl[0] & DS1305_nEOSC) {
                ds1305->ctrl[0] &= ~DS1305_nEOSC;
                write_ctrl = true;
                dev_warn(&spi->dev, "SET TIME!\n");
        }

        /* ack any pending IRQs */
        if (ds1305->ctrl[1]) {
                ds1305->ctrl[1] = 0;
                write_ctrl = true;
        }

        /* this may need one-time (re)init */
        if (pdata) {
                /* maybe enable trickle charge */
                if (((ds1305->ctrl[2] & 0xf0) != DS1305_TRICKLE_MAGIC)) {
                        ds1305->ctrl[2] = DS1305_TRICKLE_MAGIC
                                                | pdata->trickle;
                        write_ctrl = true;
                }

                /* on DS1306, configure 1 Hz signal */
                if (pdata->is_ds1306) {
                        if (pdata->en_1hz) {
                                if (!(ds1305->ctrl[0] & DS1306_1HZ)) {
                                        ds1305->ctrl[0] |= DS1306_1HZ;
                                        write_ctrl = true;
                                }
                        } else {
                                if (ds1305->ctrl[0] & DS1306_1HZ) {
                                        ds1305->ctrl[0] &= ~DS1306_1HZ;
                                        write_ctrl = true;
                                }
                        }
                }
        }

        if (write_ctrl) {
                u8              buf[4];

                buf[0] = DS1305_WRITE | DS1305_CONTROL;
                buf[1] = ds1305->ctrl[0];
                buf[2] = ds1305->ctrl[1];
                buf[3] = ds1305->ctrl[2];
                status = spi_write_then_read(spi, buf, sizeof(buf), NULL, 0);
                if (status < 0) {
                        dev_dbg(&spi->dev, "can't %s, %d\n",
                                        "write", status);
                        return status;
                }

                dev_dbg(&spi->dev, "ctrl %s: %3ph\n", "write", ds1305->ctrl);
        }

        /* see if non-Linux software set up AM/PM mode */
        addr = DS1305_HOUR;
        status = spi_write_then_read(spi, &addr, sizeof(addr),
                                &value, sizeof(value));
        if (status < 0) {
                dev_dbg(&spi->dev, "read HOUR --> %d\n", status);
                return status;
        }

        ds1305->hr12 = (DS1305_HR_12 & value) != 0;
        if (ds1305->hr12)
                dev_dbg(&spi->dev, "AM/PM\n");

        /* register RTC ... from here on, ds1305->ctrl needs locking */
        ds1305->rtc = devm_rtc_allocate_device(&spi->dev);
        if (IS_ERR(ds1305->rtc))
                return PTR_ERR(ds1305->rtc);

        ds1305->rtc->ops = &ds1305_ops;
        ds1305->rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
        ds1305->rtc->range_max = RTC_TIMESTAMP_END_2099;

        ds1305_nvmem_cfg.priv = ds1305;
        ds1305->rtc->nvram_old_abi = true;
        status = rtc_register_device(ds1305->rtc);
        if (status)
                return status;

        rtc_nvmem_register(ds1305->rtc, &ds1305_nvmem_cfg);

        /* Maybe set up alarm IRQ; be ready to handle it triggering right
         * away.  NOTE that we don't share this.  The signal is active low,
         * and we can't ack it before a SPI message delay.  We temporarily
         * disable the IRQ until it's acked, which lets us work with more
         * IRQ trigger modes (not all IRQ controllers can do falling edge).
         */
        if (spi->irq) {
                INIT_WORK(&ds1305->work, ds1305_work);
                status = devm_request_irq(&spi->dev, spi->irq, ds1305_irq,
                                0, dev_name(&ds1305->rtc->dev), ds1305);
                if (status < 0) {
                        dev_err(&spi->dev, "request_irq %d --> %d\n",
                                        spi->irq, status);
                } else {
                        device_set_wakeup_capable(&spi->dev, 1);
                }
        }

        return 0;
}

static int ds1305_remove(struct spi_device *spi)
{
        struct ds1305 *ds1305 = spi_get_drvdata(spi);

        /* carefully shut down irq and workqueue, if present */
        if (spi->irq) {
                set_bit(FLAG_EXITING, &ds1305->flags);
                devm_free_irq(&spi->dev, spi->irq, ds1305);
                cancel_work_sync(&ds1305->work);
        }

        return 0;
}

static struct spi_driver ds1305_driver = {
        .driver.name    = "rtc-ds1305",
        .probe          = ds1305_probe,
        .remove         = ds1305_remove,
        /* REVISIT add suspend/resume */
};

module_spi_driver(ds1305_driver);

MODULE_DESCRIPTION("RTC driver for DS1305 and DS1306 chips");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:rtc-ds1305");