arch/arm/mach-at91/at91rm9200_time.c

   1 /*
   2  * linux/arch/arm/mach-at91/at91rm9200_time.c
   3  *
   4  *  Copyright (C) 2003 SAN People
   5  *  Copyright (C) 2003 ATMEL
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  20  */
  21
  22 #include <linux/init.h>
  23 #include <linux/interrupt.h>
  24 #include <linux/irq.h>
  25 #include <linux/kernel.h>
  26 #include <linux/sched.h>
  27 #include <linux/time.h>
  28
  29 #include <asm/hardware.h>
  30 #include <asm/io.h>
  31 #include <asm/mach/time.h>
  32
  33 #include <asm/arch/at91_st.h>
  34
  35 static unsigned long last_crtr;
  36
  37 /*
  38  * The ST_CRTR is updated asynchronously to the master clock.  It is therefore
  39  *  necessary to read it twice (with the same value) to ensure accuracy.
  40  */
  41 static inline unsigned long read_CRTR(void) {
  42         unsigned long x1, x2;
  43
  44         do {
  45                 x1 = at91_sys_read(AT91_ST_CRTR);
  46                 x2 = at91_sys_read(AT91_ST_CRTR);
  47         } while (x1 != x2);
  48
  49         return x1;
  50 }
  51
  52 /*
  53  * Returns number of microseconds since last timer interrupt.  Note that interrupts
  54  * will have been disabled by do_gettimeofday()
  55  *  'LATCH' is hwclock ticks (see CLOCK_TICK_RATE in timex.h) per jiffy.
  56  *  'tick' is usecs per jiffy (linux/timex.h).
  57  */
  58 static unsigned long at91rm9200_gettimeoffset(void)
  59 {
  60         unsigned long elapsed;
  61
  62         elapsed = (read_CRTR() - last_crtr) & AT91_ST_ALMV;
  63
  64         return (unsigned long)(elapsed * (tick_nsec / 1000)) / LATCH;
  65 }
  66
  67 /*
  68  * IRQ handler for the timer.
  69  */
  70 static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id)
  71 {
  72         if (at91_sys_read(AT91_ST_SR) & AT91_ST_PITS) { /* This is a shared interrupt */
  73                 write_seqlock(&xtime_lock);
  74
  75                 while (((read_CRTR() - last_crtr) & AT91_ST_ALMV) >= LATCH) {
  76                         timer_tick();
  77                         last_crtr = (last_crtr + LATCH) & AT91_ST_ALMV;
  78                 }
  79
  80                 write_sequnlock(&xtime_lock);
  81
  82                 return IRQ_HANDLED;
  83         }
  84         else
  85                 return IRQ_NONE;                /* not handled */
  86 }
  87
  88 static struct irqaction at91rm9200_timer_irq = {
  89         .name           = "at91_tick",
  90         .flags          = IRQF_SHARED | IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
  91         .handler        = at91rm9200_timer_interrupt
  92 };
  93
  94 void at91rm9200_timer_reset(void)
  95 {
  96         last_crtr = 0;
  97
  98         /* Real time counter incremented every 30.51758 microseconds */
  99         at91_sys_write(AT91_ST_RTMR, 1);
 100
 101         /* Set Period Interval timer */
 102         at91_sys_write(AT91_ST_PIMR, LATCH);
 103
 104         /* Clear any pending interrupts */
 105         (void) at91_sys_read(AT91_ST_SR);
 106
 107         /* Enable Period Interval Timer interrupt */
 108         at91_sys_write(AT91_ST_IER, AT91_ST_PITS);
 109 }
 110
 111 /*
 112  * Set up timer interrupt.
 113  */
 114 void __init at91rm9200_timer_init(void)
 115 {
 116         /* Disable all timer interrupts */
 117         at91_sys_write(AT91_ST_IDR, AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
 118         (void) at91_sys_read(AT91_ST_SR);       /* Clear any pending interrupts */
 119
 120         /* Make IRQs happen for the system timer */
 121         setup_irq(AT91_ID_SYS, &at91rm9200_timer_irq);
 122
 123         /* Change the kernel's 'tick' value to 10009 usec. (the default is 10000) */
 124         tick_usec = (LATCH * 1000000) / CLOCK_TICK_RATE;
 125
 126         /* Initialize and enable the timer interrupt */
 127         at91rm9200_timer_reset();
 128 }
 129
 130 #ifdef CONFIG_PM
 131 static void at91rm9200_timer_suspend(void)
 132 {
 133         /* disable Period Interval Timer interrupt */
 134         at91_sys_write(AT91_ST_IDR, AT91_ST_PITS);
 135 }
 136 #else
 137 #define at91rm9200_timer_suspend        NULL
 138 #endif
 139
 140 struct sys_timer at91rm9200_timer = {
 141         .init           = at91rm9200_timer_init,
 142         .offset         = at91rm9200_gettimeoffset,
 143         .suspend        = at91rm9200_timer_suspend,
 144         .resume         = at91rm9200_timer_reset,
 145 };
 146