Portability cleanup as required by Linus.

[linux-2.6/linux-mips.git] / drivers / char / rtc.c

/*
 *      Real Time Clock interface for Linux     
 *
 *      Copyright (C) 1996 Paul Gortmaker
 *
 *      This driver allows use of the real time clock (built into
 *      nearly all computers) from user space. It exports the /dev/rtc
 *      interface supporting various ioctl() and also the
 *      /proc/driver/rtc pseudo-file for status information.
 *
 *      The ioctls can be used to set the interrupt behaviour and
 *      generation rate from the RTC via IRQ 8. Then the /dev/rtc
 *      interface can be used to make use of these timer interrupts,
 *      be they interval or alarm based.
 *
 *      The /dev/rtc interface will block on reads until an interrupt
 *      has been received. If a RTC interrupt has already happened,
 *      it will output an unsigned long and then block. The output value
 *      contains the interrupt status in the low byte and the number of
 *      interrupts since the last read in the remaining high bytes. The 
 *      /dev/rtc interface can also be used with the select(2) call.
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 *
 *      Based on other minimal char device drivers, like Alan's
 *      watchdog, Ted's random, etc. etc.
 *
 *      1.07    Paul Gortmaker.
 *      1.08    Miquel van Smoorenburg: disallow certain things on the
 *              DEC Alpha as the CMOS clock is also used for other things.
 *      1.09    Nikita Schmidt: epoch support and some Alpha cleanup.
 *      1.09a   Pete Zaitcev: Sun SPARC
 *      1.09b   Jeff Garzik: Modularize, init cleanup
 *      1.09c   Jeff Garzik: SMP cleanup
 *      1.10    Paul Barton-Davis: add support for async I/O
 *      1.10a   Andrea Arcangeli: Alpha updates
 *      1.10b   Andrew Morton: SMP lock fix
 *      1.10c   Cesar Barros: SMP locking fixes and cleanup
 */

#define RTC_VERSION             "1.10c"

#define RTC_IO_EXTENT   0x10    /* Only really two ports, but...        */

/*
 *      Note that *all* calls to CMOS_READ and CMOS_WRITE are done with
 *      interrupts disabled. Due to the index-port/data-port (0x70/0x71)
 *      design of the RTC, we don't want two different things trying to
 *      get to it at once. (e.g. the periodic 11 min sync from time.c vs.
 *      this driver.)
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/miscdevice.h>
#include <linux/ioport.h>
#include <linux/fcntl.h>
#include <linux/mc146818rtc.h>
#include <linux/init.h>
#include <linux/poll.h>
#include <linux/proc_fs.h>
#include <linux/spinlock.h>

#include <asm/io.h>
#include <asm/uaccess.h>
#include <asm/system.h>

#ifdef __sparc__
#include <asm/ebus.h>

static unsigned long rtc_port;
static int rtc_irq;
#endif

/*
 *      We sponge a minor off of the misc major. No need slurping
 *      up another valuable major dev number for this. If you add
 *      an ioctl, make sure you don't conflict with SPARC's RTC
 *      ioctls.
 */

static struct fasync_struct *rtc_async_queue;

static DECLARE_WAIT_QUEUE_HEAD(rtc_wait);

extern spinlock_t rtc_lock;

static struct timer_list rtc_irq_timer;

static loff_t rtc_llseek(struct file *file, loff_t offset, int origin);

static ssize_t rtc_read(struct file *file, char *buf,
                        size_t count, loff_t *ppos);

static int rtc_ioctl(struct inode *inode, struct file *file,
                     unsigned int cmd, unsigned long arg);

#if RTC_IRQ
static unsigned int rtc_poll(struct file *file, poll_table *wait);
#endif

static void get_rtc_time (struct rtc_time *rtc_tm);
static void get_rtc_alm_time (struct rtc_time *alm_tm);
#if RTC_IRQ
static void rtc_dropped_irq(unsigned long data);

static void set_rtc_irq_bit(unsigned char bit);
static void mask_rtc_irq_bit(unsigned char bit);
#endif

static inline unsigned char rtc_is_updating(void);

static int rtc_read_proc(char *page, char **start, off_t off,
                         int count, int *eof, void *data);

/*
 *      Bits in rtc_status. (6 bits of room for future expansion)
 */

#define RTC_IS_OPEN             0x01    /* means /dev/rtc is in use     */
#define RTC_TIMER_ON            0x02    /* missed irq timer active      */

/*
 * rtc_status is never changed by rtc_interrupt, and ioctl/open/close is
 * protected by the big kernel lock. However, ioctl can still disable the timer
 * in rtc_status and then with del_timer after the interrupt has read
 * rtc_status but before mod_timer is called, which would then reenable the
 * timer (but you would need to have an awful timing before you'd trip on it)
 */
static unsigned long rtc_status = 0;    /* bitmapped status byte.       */
static unsigned long rtc_freq = 0;      /* Current periodic IRQ rate    */
static unsigned long rtc_irq_data = 0;  /* our output to the world      */

/*
 *      If this driver ever becomes modularised, it will be really nice
 *      to make the epoch retain its value across module reload...
 */

static unsigned long epoch = 1900;      /* year corresponding to 0x00   */

static const unsigned char days_in_mo[] = 
{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

#if RTC_IRQ
/*
 *      A very tiny interrupt handler. It runs with SA_INTERRUPT set,
 *      but there is possibility of conflicting with the set_rtc_mmss()
 *      call (the rtc irq and the timer irq can easily run at the same
 *      time in two different CPUs). So we need to serializes
 *      accesses to the chip with the rtc_lock spinlock that each
 *      architecture should implement in the timer code.
 *      (See ./arch/XXXX/kernel/time.c for the set_rtc_mmss() function.)
 */

static void rtc_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
        /*
         *      Can be an alarm interrupt, update complete interrupt,
         *      or a periodic interrupt. We store the status in the
         *      low byte and the number of interrupts received since
         *      the last read in the remainder of rtc_irq_data.
         */

        spin_lock (&rtc_lock);
        rtc_irq_data += 0x100;
        rtc_irq_data &= ~0xff;
        rtc_irq_data |= (CMOS_READ(RTC_INTR_FLAGS) & 0xF0);

        if (rtc_status & RTC_TIMER_ON)
                mod_timer(&rtc_irq_timer, jiffies + HZ/rtc_freq + 2*HZ/100);

        spin_unlock (&rtc_lock);

        /* Now do the rest of the actions */
        wake_up_interruptible(&rtc_wait);       

        kill_fasync (&rtc_async_queue, SIGIO, POLL_IN);
}
#endif

/*
 *      Now all the various file operations that we export.
 */

static loff_t rtc_llseek(struct file *file, loff_t offset, int origin)
{
        return -ESPIPE;
}

static ssize_t rtc_read(struct file *file, char *buf,
                        size_t count, loff_t *ppos)
{
#if !RTC_IRQ
        return -EIO;
#else
        DECLARE_WAITQUEUE(wait, current);
        unsigned long data;
        ssize_t retval;
        
        if (count < sizeof(unsigned long))
                return -EINVAL;

        add_wait_queue(&rtc_wait, &wait);

        current->state = TASK_INTERRUPTIBLE;
                
        do {
                /* First make it right. Then make it fast. Putting this whole
                 * block within the parentheses of a while would be too
                 * confusing. And no, xchg() is not the answer. */
                spin_lock_irq (&rtc_lock);
                data = rtc_irq_data;
                rtc_irq_data = 0;
                spin_unlock_irq (&rtc_lock);

                if (data != 0)
                        break;

                if (file->f_flags & O_NONBLOCK) {
                        retval = -EAGAIN;
                        goto out;
                }
                if (signal_pending(current)) {
                        retval = -ERESTARTSYS;
                        goto out;
                }
                schedule();
        } while (1);

        retval = put_user(data, (unsigned long *)buf); 
        if (!retval)
                retval = sizeof(unsigned long); 
 out:
        current->state = TASK_RUNNING;
        remove_wait_queue(&rtc_wait, &wait);

        return retval;
#endif
}

static int rtc_ioctl(struct inode *inode, struct file *file, unsigned int cmd,
                     unsigned long arg)
{
        struct rtc_time wtime; 

        switch (cmd) {
#if RTC_IRQ
        case RTC_AIE_OFF:       /* Mask alarm int. enab. bit    */
        {
                mask_rtc_irq_bit(RTC_AIE);
                return 0;
        }
        case RTC_AIE_ON:        /* Allow alarm interrupts.      */
        {
                set_rtc_irq_bit(RTC_AIE);
                return 0;
        }
        case RTC_PIE_OFF:       /* Mask periodic int. enab. bit */
        {
                mask_rtc_irq_bit(RTC_PIE);
                if (rtc_status & RTC_TIMER_ON) {
                        spin_lock_irq (&rtc_lock);
                        rtc_status &= ~RTC_TIMER_ON;
                        del_timer(&rtc_irq_timer);
                        spin_unlock_irq (&rtc_lock);
                }
                return 0;
        }
        case RTC_PIE_ON:        /* Allow periodic ints          */
        {

                /*
                 * We don't really want Joe User enabling more
                 * than 64Hz of interrupts on a multi-user machine.
                 */
                if ((rtc_freq > 64) && (!capable(CAP_SYS_RESOURCE)))
                        return -EACCES;

                if (!(rtc_status & RTC_TIMER_ON)) {
                        spin_lock_irq (&rtc_lock);
                        rtc_irq_timer.expires = jiffies + HZ/rtc_freq + 2*HZ/100;
                        add_timer(&rtc_irq_timer);
                        rtc_status |= RTC_TIMER_ON;
                        spin_unlock_irq (&rtc_lock);
                }
                set_rtc_irq_bit(RTC_PIE);
                return 0;
        }
        case RTC_UIE_OFF:       /* Mask ints from RTC updates.  */
        {
                mask_rtc_irq_bit(RTC_UIE);
                return 0;
        }
        case RTC_UIE_ON:        /* Allow ints for RTC updates.  */
        {
                set_rtc_irq_bit(RTC_UIE);
                return 0;
        }
#endif
        case RTC_ALM_READ:      /* Read the present alarm time */
        {
                /*
                 * This returns a struct rtc_time. Reading >= 0xc0
                 * means "don't care" or "match all". Only the tm_hour,
                 * tm_min, and tm_sec values are filled in.
                 */

                get_rtc_alm_time(&wtime);
                break; 
        }
        case RTC_ALM_SET:       /* Store a time into the alarm */
        {
                /*
                 * This expects a struct rtc_time. Writing 0xff means
                 * "don't care" or "match all". Only the tm_hour,
                 * tm_min and tm_sec are used.
                 */
                unsigned char hrs, min, sec;
                struct rtc_time alm_tm;

                if (copy_from_user(&alm_tm, (struct rtc_time*)arg,
                                   sizeof(struct rtc_time)))
                        return -EFAULT;

                hrs = alm_tm.tm_hour;
                min = alm_tm.tm_min;
                sec = alm_tm.tm_sec;

                if (hrs >= 24)
                        hrs = 0xff;

                if (min >= 60)
                        min = 0xff;

                if (sec >= 60)
                        sec = 0xff;

                spin_lock_irq(&rtc_lock);
                if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) ||
                    RTC_ALWAYS_BCD)
                {
                        BIN_TO_BCD(sec);
                        BIN_TO_BCD(min);
                        BIN_TO_BCD(hrs);
                }
                CMOS_WRITE(hrs, RTC_HOURS_ALARM);
                CMOS_WRITE(min, RTC_MINUTES_ALARM);
                CMOS_WRITE(sec, RTC_SECONDS_ALARM);
                spin_unlock_irq(&rtc_lock);

                return 0;
        }
        case RTC_RD_TIME:       /* Read the time/date from RTC  */
        {
                get_rtc_time(&wtime);
                break;
        }
        case RTC_SET_TIME:      /* Set the RTC */
        {
                struct rtc_time rtc_tm;
                unsigned char mon, day, hrs, min, sec, leap_yr;
                unsigned char save_control, save_freq_select;
                unsigned int yrs;

                if (!capable(CAP_SYS_TIME))
                        return -EACCES;

                if (copy_from_user(&rtc_tm, (struct rtc_time*)arg,
                                   sizeof(struct rtc_time)))
                        return -EFAULT;

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

                if (yrs < 1970)
                        return -EINVAL;

                leap_yr = ((!(yrs % 4) && (yrs % 100)) || !(yrs % 400));

                if ((mon > 12) || (day == 0))
                        return -EINVAL;

                if (day > (days_in_mo[mon] + ((mon == 2) && leap_yr)))
                        return -EINVAL;
                        
                if ((hrs >= 24) || (min >= 60) || (sec >= 60))
                        return -EINVAL;

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

                spin_lock_irq(&rtc_lock);
                if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY)
                    || RTC_ALWAYS_BCD) {
                        if (yrs > 169) {
                                spin_unlock_irq(&rtc_lock);
                                return -EINVAL;
                        }
                        if (yrs >= 100)
                                yrs -= 100;

                        BIN_TO_BCD(sec);
                        BIN_TO_BCD(min);
                        BIN_TO_BCD(hrs);
                        BIN_TO_BCD(day);
                        BIN_TO_BCD(mon);
                        BIN_TO_BCD(yrs);
                }

                save_control = CMOS_READ(RTC_CONTROL);
                CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
                save_freq_select = CMOS_READ(RTC_FREQ_SELECT);
                CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);

                CMOS_WRITE(yrs, RTC_YEAR);
                CMOS_WRITE(mon, RTC_MONTH);
                CMOS_WRITE(day, RTC_DAY_OF_MONTH);
                CMOS_WRITE(hrs, RTC_HOURS);
                CMOS_WRITE(min, RTC_MINUTES);
                CMOS_WRITE(sec, RTC_SECONDS);

                CMOS_WRITE(save_control, RTC_CONTROL);
                CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);

                spin_unlock_irq(&rtc_lock);
                return 0;
        }
#if RTC_IRQ
        case RTC_IRQP_READ:     /* Read the periodic IRQ rate.  */
        {
                return put_user(rtc_freq, (unsigned long *)arg);
        }
        case RTC_IRQP_SET:      /* Set periodic IRQ rate.       */
        {
                int tmp = 0;
                unsigned char val;

                /* 
                 * The max we can do is 8192Hz.
                 */
                if ((arg < 2) || (arg > 8192))
                        return -EINVAL;
                /*
                 * We don't really want Joe User generating more
                 * than 64Hz of interrupts on a multi-user machine.
                 */
                if ((arg > 64) && (!capable(CAP_SYS_RESOURCE)))
                        return -EACCES;

                while (arg > (1<<tmp))
                        tmp++;

                /*
                 * Check that the input was really a power of 2.
                 */
                if (arg != (1<<tmp))
                        return -EINVAL;

                spin_lock_irq(&rtc_lock);
                rtc_freq = arg;

                val = CMOS_READ(RTC_FREQ_SELECT) & 0xf0;
                val |= (16 - tmp);
                CMOS_WRITE(val, RTC_FREQ_SELECT);
                spin_unlock_irq(&rtc_lock);
                return 0;
        }
#elif !defined(CONFIG_DECSTATION)
        case RTC_EPOCH_READ:    /* Read the epoch.      */
        {
                return put_user (epoch, (unsigned long *)arg);
        }
        case RTC_EPOCH_SET:     /* Set the epoch.       */
        {
                /* 
                 * There were no RTC clocks before 1900.
                 */
                if (arg < 1900)
                        return -EINVAL;

                if (!capable(CAP_SYS_TIME))
                        return -EACCES;

                epoch = arg;
                return 0;
        }
#endif
        default:
                return -EINVAL;
        }
        return copy_to_user((void *)arg, &wtime, sizeof wtime) ? -EFAULT : 0;
}

/*
 *      We enforce only one user at a time here with the open/close.
 *      Also clear the previous interrupt data on an open, and clean
 *      up things on a close.
 */

/* We use rtc_lock to protect against concurrent opens. So the BKL is not
 * needed here. Or anywhere else in this driver. */
static int rtc_open(struct inode *inode, struct file *file)
{
        spin_lock_irq (&rtc_lock);

        if(rtc_status & RTC_IS_OPEN)
                goto out_busy;

        rtc_status |= RTC_IS_OPEN;

        rtc_irq_data = 0;
        spin_unlock_irq (&rtc_lock);
        return 0;

out_busy:
        spin_unlock_irq (&rtc_lock);
        return -EBUSY;
}

static int rtc_fasync (int fd, struct file *filp, int on)

{
        return fasync_helper (fd, filp, on, &rtc_async_queue);
}

static int rtc_release(struct inode *inode, struct file *file)
{
#if RTC_IRQ
        /*
         * Turn off all interrupts once the device is no longer
         * in use, and clear the data.
         */

        unsigned char tmp;

        spin_lock_irq(&rtc_lock);
        tmp = CMOS_READ(RTC_CONTROL);
        tmp &=  ~RTC_PIE;
        tmp &=  ~RTC_AIE;
        tmp &=  ~RTC_UIE;
        CMOS_WRITE(tmp, RTC_CONTROL);
        CMOS_READ(RTC_INTR_FLAGS);

        if (rtc_status & RTC_TIMER_ON) {
                rtc_status &= ~RTC_TIMER_ON;
                del_timer(&rtc_irq_timer);
        }
        spin_unlock_irq(&rtc_lock);

        if (file->f_flags & FASYNC) {
                rtc_fasync (-1, file, 0);
        }
#endif

        spin_lock_irq (&rtc_lock);
        rtc_irq_data = 0;
        spin_unlock_irq (&rtc_lock);

        /* No need for locking -- nobody else can do anything until this rmw is
         * committed, and no timer is running. */
        rtc_status &= ~RTC_IS_OPEN;
        return 0;
}

#if RTC_IRQ
/* Called without the kernel lock - fine */
static unsigned int rtc_poll(struct file *file, poll_table *wait)
{
        unsigned long l;

        poll_wait(file, &rtc_wait, wait);

        spin_lock_irq (&rtc_lock);
        l = rtc_irq_data;
        spin_unlock_irq (&rtc_lock);

        if (l != 0)
                return POLLIN | POLLRDNORM;
        return 0;
}
#endif

/*
 *      The various file operations we support.
 */

static struct file_operations rtc_fops = {
        owner:          THIS_MODULE,
        llseek:         rtc_llseek,
        read:           rtc_read,
#if RTC_IRQ
        poll:           rtc_poll,
#endif
        ioctl:          rtc_ioctl,
        open:           rtc_open,
        release:        rtc_release,
        fasync:         rtc_fasync,
};

static struct miscdevice rtc_dev=
{
        RTC_MINOR,
        "rtc",
        &rtc_fops
};

static int __init rtc_init(void)
{
#if defined(__alpha__) || defined(__mips__)
        unsigned int year, ctrl;
        unsigned long uip_watchdog;
        char *guess = NULL;
#endif
#ifdef __sparc__
        struct linux_ebus *ebus;
        struct linux_ebus_device *edev;
#endif

#ifdef __sparc__
        for_each_ebus(ebus) {
                for_each_ebusdev(edev, ebus) {
                        if(strcmp(edev->prom_name, "rtc") == 0) {
                                goto found;
                        }
                }
        }
        printk("rtc_init: no PC rtc found\n");
        return -EIO;

found:
        rtc_port = edev->resource[0].start;
        rtc_irq = edev->irqs[0];
        /*
         * XXX Interrupt pin #7 in Espresso is shared between RTC and
         * PCI Slot 2 INTA# (and some INTx# in Slot 1). SA_INTERRUPT here
         * is asking for trouble with add-on boards. Change to SA_SHIRQ.
         */
        if(request_irq(rtc_irq, rtc_interrupt, SA_INTERRUPT, "rtc", (void *)&rtc_port)) {
                /*
                 * Standard way for sparc to print irq's is to use
                 * __irq_itoa(). I think for EBus it's ok to use %d.
                 */
                printk("rtc: cannot register IRQ %d\n", rtc_irq);
                return -EIO;
        }
#else
        if (check_region (RTC_PORT (0), RTC_IO_EXTENT))
        {
                printk(KERN_ERR "rtc: I/O port %d is not free.\n", RTC_PORT (0));
                return -EIO;
        }

#if RTC_IRQ
        if(request_irq(RTC_IRQ, rtc_interrupt, SA_INTERRUPT, "rtc", NULL))
        {
                /* Yeah right, seeing as irq 8 doesn't even hit the bus. */
                printk(KERN_ERR "rtc: IRQ %d is not free.\n", RTC_IRQ);
                return -EIO;
        }
#endif

        request_region(RTC_PORT(0), RTC_IO_EXTENT, "rtc");
#endif /* __sparc__ vs. others */

        misc_register(&rtc_dev);
        create_proc_read_entry ("driver/rtc", 0, 0, rtc_read_proc, NULL);

#if defined(__alpha__) || defined(__mips__)
        rtc_freq = HZ;
        
        /* Each operating system on an Alpha uses its own epoch.
           Let's try to guess which one we are using now. */
        
        uip_watchdog = jiffies;
        if (rtc_is_updating() != 0)
                while (jiffies - uip_watchdog < 2*HZ/100)
                        barrier();
        
        spin_lock_irq(&rtc_lock);
        year = CMOS_READ(RTC_YEAR);
        ctrl = CMOS_READ(RTC_CONTROL);
        spin_unlock_irq(&rtc_lock);
        
        if (!(ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
                BCD_TO_BIN(year);       /* This should never happen... */
        
        if (year > 20 && year < 48) {
                epoch = 1980;
                guess = "ARC console";
        } else if (year >= 48 && year < 70) {
                epoch = 1952;
                guess = "Digital UNIX";
        } else if (year >= 70 && year < 100) {
                epoch = 1928;
                guess = "Digital DECstation";
        }
        if (guess)
                printk("rtc: %s epoch (%lu) detected\n", guess, epoch);
#endif
#if RTC_IRQ
        init_timer(&rtc_irq_timer);
        rtc_irq_timer.function = rtc_dropped_irq;
        spin_lock_irq(&rtc_lock);
        /* Initialize periodic freq. to CMOS reset default, which is 1024Hz */
        CMOS_WRITE(((CMOS_READ(RTC_FREQ_SELECT) & 0xF0) | 0x06), RTC_FREQ_SELECT);
        spin_unlock_irq(&rtc_lock);
        rtc_freq = 1024;
#endif

        printk(KERN_INFO "Real Time Clock Driver v" RTC_VERSION "\n");

        return 0;
}

static void __exit rtc_exit (void)
{
        /* interrupts and maybe timer disabled at this point by rtc_release */
        /* FIXME: Maybe??? */

        if (rtc_status & RTC_TIMER_ON) {
                spin_lock_irq (&rtc_lock);
                rtc_status &= ~RTC_TIMER_ON;
                del_timer(&rtc_irq_timer);
                spin_unlock_irq (&rtc_lock);

                printk(KERN_WARNING "rtc_exit(), and timer still running.\n");
        }

        remove_proc_entry ("driver/rtc", NULL);
        misc_deregister(&rtc_dev);

#ifdef __sparc__
        free_irq (rtc_irq, &rtc_port);
#else
        release_region (RTC_PORT (0), RTC_IO_EXTENT);
#if RTC_IRQ
        free_irq (RTC_IRQ, NULL);
#endif
#endif /* __sparc__ */
}

module_init(rtc_init);
module_exit(rtc_exit);
EXPORT_NO_SYMBOLS;

#if RTC_IRQ
/*
 *      At IRQ rates >= 4096Hz, an interrupt may get lost altogether.
 *      (usually during an IDE disk interrupt, with IRQ unmasking off)
 *      Since the interrupt handler doesn't get called, the IRQ status
 *      byte doesn't get read, and the RTC stops generating interrupts.
 *      A timer is set, and will call this function if/when that happens.
 *      To get it out of this stalled state, we just read the status.
 *      At least a jiffy of interrupts (rtc_freq/HZ) will have been lost.
 *      (You *really* shouldn't be trying to use a non-realtime system 
 *      for something that requires a steady > 1KHz signal anyways.)
 */

static void rtc_dropped_irq(unsigned long data)
{
        unsigned long freq;

        spin_lock_irq (&rtc_lock);

        /* Just in case someone disabled the timer from behind our back... */
        if (rtc_status & RTC_TIMER_ON)
                mod_timer(&rtc_irq_timer, jiffies + HZ/rtc_freq + 2*HZ/100);

        rtc_irq_data += ((rtc_freq/HZ)<<8);
        rtc_irq_data &= ~0xff;
        rtc_irq_data |= (CMOS_READ(RTC_INTR_FLAGS) & 0xF0);     /* restart */

        freq = rtc_freq;

        spin_unlock_irq(&rtc_lock);

        printk(KERN_INFO "rtc: lost some interrupts at %ldHz.\n", freq);

        /* Now we have new data */
        wake_up_interruptible(&rtc_wait);

        kill_fasync (&rtc_async_queue, SIGIO, POLL_IN);
}
#endif

/*
 *      Info exported via "/proc/driver/rtc".
 */

static int rtc_proc_output (char *buf)
{
#define YN(bit) ((ctrl & bit) ? "yes" : "no")
#define NY(bit) ((ctrl & bit) ? "no" : "yes")
        char *p;
        struct rtc_time tm;
        unsigned char batt, ctrl;
        unsigned long freq;

        spin_lock_irq(&rtc_lock);
        batt = CMOS_READ(RTC_VALID) & RTC_VRT;
        ctrl = CMOS_READ(RTC_CONTROL);
        freq = rtc_freq;
        spin_unlock_irq(&rtc_lock);

        p = buf;

        get_rtc_time(&tm);

        /*
         * There is no way to tell if the luser has the RTC set for local
         * time or for Universal Standard Time (GMT). Probably local though.
         */
        p += sprintf(p,
                     "rtc_time\t: %02d:%02d:%02d\n"
                     "rtc_date\t: %04d-%02d-%02d\n"
                     "rtc_epoch\t: %04lu\n",
                     tm.tm_hour, tm.tm_min, tm.tm_sec,
                     tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday, epoch);

        get_rtc_alm_time(&tm);

        /*
         * We implicitly assume 24hr mode here. Alarm values >= 0xc0 will
         * match any value for that particular field. Values that are
         * greater than a valid time, but less than 0xc0 shouldn't appear.
         */
        p += sprintf(p, "alarm\t\t: ");
        if (tm.tm_hour <= 24)
                p += sprintf(p, "%02d:", tm.tm_hour);
        else
                p += sprintf(p, "**:");

        if (tm.tm_min <= 59)
                p += sprintf(p, "%02d:", tm.tm_min);
        else
                p += sprintf(p, "**:");

        if (tm.tm_sec <= 59)
                p += sprintf(p, "%02d\n", tm.tm_sec);
        else
                p += sprintf(p, "**\n");

        p += sprintf(p,
                     "DST_enable\t: %s\n"
                     "BCD\t\t: %s\n"
                     "24hr\t\t: %s\n"
                     "square_wave\t: %s\n"
                     "alarm_IRQ\t: %s\n"
                     "update_IRQ\t: %s\n"
                     "periodic_IRQ\t: %s\n"
                     "periodic_freq\t: %ld\n"
                     "batt_status\t: %s\n",
                     YN(RTC_DST_EN),
                     NY(RTC_DM_BINARY),
                     YN(RTC_24H),
                     YN(RTC_SQWE),
                     YN(RTC_AIE),
                     YN(RTC_UIE),
                     YN(RTC_PIE),
                     freq,
                     batt ? "okay" : "dead");

        return  p - buf;
#undef YN
#undef NY
}

static int rtc_read_proc(char *page, char **start, off_t off,
                         int count, int *eof, void *data)
{
        int len = rtc_proc_output (page);
        if (len <= off+count) *eof = 1;
        *start = page + off;
        len -= off;
        if (len>count) len = count;
        if (len<0) len = 0;
        return len;
}

/*
 * Returns true if a clock update is in progress
 */
/* FIXME shouldn't this be above rtc_init to make it fully inlined? */
static inline unsigned char rtc_is_updating(void)
{
        unsigned char uip;

        spin_lock_irq(&rtc_lock);
        uip = (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP);
        spin_unlock_irq(&rtc_lock);
        return uip;
}

static void get_rtc_time(struct rtc_time *rtc_tm)
{
        unsigned long uip_watchdog = jiffies;
        unsigned char ctrl;

        /*
         * read RTC once any update in progress is done. The update
         * can take just over 2ms. We wait 10 to 20ms. There is no need to
         * to poll-wait (up to 1s - eeccch) for the falling edge of RTC_UIP.
         * If you need to know *exactly* when a second has started, enable
         * periodic update complete interrupts, (via ioctl) and then 
         * immediately read /dev/rtc which will block until you get the IRQ.
         * Once the read clears, read the RTC time (again via ioctl). Easy.
         */

        if (rtc_is_updating() != 0)
                while (jiffies - uip_watchdog < 2*HZ/100)
                        barrier();

        /*
         * 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(&rtc_lock);
        rtc_tm->tm_sec = CMOS_READ(RTC_SECONDS);
        rtc_tm->tm_min = CMOS_READ(RTC_MINUTES);
        rtc_tm->tm_hour = CMOS_READ(RTC_HOURS);
        rtc_tm->tm_mday = CMOS_READ(RTC_DAY_OF_MONTH);
        rtc_tm->tm_mon = CMOS_READ(RTC_MONTH);
        rtc_tm->tm_year = CMOS_READ(RTC_YEAR);
        ctrl = CMOS_READ(RTC_CONTROL);
        spin_unlock_irq(&rtc_lock);

        if (!(ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
        {
                BCD_TO_BIN(rtc_tm->tm_sec);
                BCD_TO_BIN(rtc_tm->tm_min);
                BCD_TO_BIN(rtc_tm->tm_hour);
                BCD_TO_BIN(rtc_tm->tm_mday);
                BCD_TO_BIN(rtc_tm->tm_mon);
                BCD_TO_BIN(rtc_tm->tm_year);
        }

        /*
         * Account for differences between how the RTC uses the values
         * and how they are defined in a struct rtc_time;
         */
        if ((rtc_tm->tm_year += (epoch - 1900)) <= 69)
                rtc_tm->tm_year += 100;

        rtc_tm->tm_mon--;
}

static void get_rtc_alm_time(struct rtc_time *alm_tm)
{
        unsigned char ctrl;

        /*
         * Only the values that we read from the RTC are set. That
         * means only tm_hour, tm_min, and tm_sec.
         */
        spin_lock_irq(&rtc_lock);
        alm_tm->tm_sec = CMOS_READ(RTC_SECONDS_ALARM);
        alm_tm->tm_min = CMOS_READ(RTC_MINUTES_ALARM);
        alm_tm->tm_hour = CMOS_READ(RTC_HOURS_ALARM);
        ctrl = CMOS_READ(RTC_CONTROL);
        spin_unlock_irq(&rtc_lock);

        if (!(ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
        {
                BCD_TO_BIN(alm_tm->tm_sec);
                BCD_TO_BIN(alm_tm->tm_min);
                BCD_TO_BIN(alm_tm->tm_hour);
        }
}

#if RTC_IRQ
/*
 * Used to disable/enable interrupts for any one of UIE, AIE, PIE.
 * Rumour has it that if you frob the interrupt enable/disable
 * bits in RTC_CONTROL, you should read RTC_INTR_FLAGS, to
 * ensure you actually start getting interrupts. Probably for
 * compatibility with older/broken chipset RTC implementations.
 * We also clear out any old irq data after an ioctl() that
 * meddles with the interrupt enable/disable bits.
 */

static void mask_rtc_irq_bit(unsigned char bit)
{
        unsigned char val;

        spin_lock_irq(&rtc_lock);
        val = CMOS_READ(RTC_CONTROL);
        val &=  ~bit;
        CMOS_WRITE(val, RTC_CONTROL);
        CMOS_READ(RTC_INTR_FLAGS);

        rtc_irq_data = 0;
        spin_unlock_irq(&rtc_lock);
}

static void set_rtc_irq_bit(unsigned char bit)
{
        unsigned char val;

        spin_lock_irq(&rtc_lock);
        val = CMOS_READ(RTC_CONTROL);
        val |= bit;
        CMOS_WRITE(val, RTC_CONTROL);
        CMOS_READ(RTC_INTR_FLAGS);

        rtc_irq_data = 0;
        spin_unlock_irq(&rtc_lock);
}
#endif