arch/arm/mach-sa1100/time.c

   1 /*
   2  * linux/arch/arm/mach-sa1100/time.c
   3  *
   4  * Copyright (C) 1998 Deborah Wallach.
   5  * Twiddles  (C) 1999   Hugo Fiennes <hugo@empeg.com>
   6  *
   7  * 2000/03/29 (C) Nicolas Pitre <nico@cam.org>
   8  *      Rewritten: big cleanup, much simpler, better HZ accuracy.
   9  *
  10  */
  11 #include <linux/init.h>
  12 #include <linux/errno.h>
  13 #include <linux/interrupt.h>
  14 #include <linux/timex.h>
  15 #include <linux/signal.h>
  16
  17 #include <asm/mach/time.h>
  18 #include <asm/hardware.h>
  19
  20 #define RTC_DEF_DIVIDER         (32768 - 1)
  21 #define RTC_DEF_TRIM            0
  22
  23 static unsigned long __init sa1100_get_rtc_time(void)
  24 {
  25         /*
  26          * According to the manual we should be able to let RTTR be zero
  27          * and then a default diviser for a 32.768KHz clock is used.
  28          * Apparently this doesn't work, at least for my SA1110 rev 5.
  29          * If the clock divider is uninitialized then reset it to the
  30          * default value to get the 1Hz clock.
  31          */
  32         if (RTTR == 0) {
  33                 RTTR = RTC_DEF_DIVIDER + (RTC_DEF_TRIM << 16);
  34                 printk(KERN_WARNING "Warning: uninitialized Real Time Clock\n");
  35                 /* The current RTC value probably doesn't make sense either */
  36                 RCNR = 0;
  37                 return 0;
  38         }
  39         return RCNR;
  40 }
  41
  42 static int sa1100_set_rtc(void)
  43 {
  44         unsigned long current_time = xtime.tv_sec;
  45
  46         if (RTSR & RTSR_ALE) {
  47                 /* make sure not to forward the clock over an alarm */
  48                 unsigned long alarm = RTAR;
  49                 if (current_time >= alarm && alarm >= RCNR)
  50                         return -ERESTARTSYS;
  51         }
  52         RCNR = current_time;
  53         return 0;
  54 }
  55
  56 /* IRQs are disabled before entering here from do_gettimeofday() */
  57 static unsigned long sa1100_gettimeoffset (void)
  58 {
  59         unsigned long ticks_to_match, elapsed, usec;
  60
  61         /* Get ticks before next timer match */
  62         ticks_to_match = OSMR0 - OSCR;
  63
  64         /* We need elapsed ticks since last match */
  65         elapsed = LATCH - ticks_to_match;
  66
  67         /* Now convert them to usec */
  68         usec = (unsigned long)(elapsed * (tick_nsec / 1000))/LATCH;
  69
  70         return usec;
  71 }
  72
  73 /*
  74  * We will be entered with IRQs enabled.
  75  *
  76  * Loop until we get ahead of the free running timer.
  77  * This ensures an exact clock tick count and time accuracy.
  78  * IRQs are disabled inside the loop to ensure coherence between
  79  * lost_ticks (updated in do_timer()) and the match reg value, so we
  80  * can use do_gettimeofday() from interrupt handlers.
  81  */
  82 static irqreturn_t
  83 sa1100_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
  84 {
  85         unsigned int next_match;
  86
  87         do {
  88                 timer_tick(regs);
  89                 OSSR = OSSR_M0;  /* Clear match on timer 0 */
  90                 next_match = (OSMR0 += LATCH);
  91         } while ((signed long)(next_match - OSCR) <= 0);
  92
  93         return IRQ_HANDLED;
  94 }
  95
  96 static struct irqaction sa1100_timer_irq = {
  97         .name           = "SA11xx Timer Tick",
  98         .flags          = SA_INTERRUPT,
  99         .handler        = sa1100_timer_interrupt
 100 };
 101
 102 void __init sa1100_init_time(void)
 103 {
 104         struct timespec tv;
 105
 106         gettimeoffset = sa1100_gettimeoffset;
 107         set_rtc = sa1100_set_rtc;
 108
 109         tv.tv_nsec = 0;
 110         tv.tv_sec = sa1100_get_rtc_time();
 111         do_settimeofday(&tv);
 112
 113         OSMR0 = 0;              /* set initial match at 0 */
 114         OSSR = 0xf;             /* clear status on all timers */
 115         setup_irq(IRQ_OST0, &sa1100_timer_irq);
 116         OIER |= OIER_E0;        /* enable match on timer 0 to cause interrupts */
 117         OSCR = 0;               /* initialize free-running timer, force first match */
 118 }
 119