arch/arm/cpu/arm920t/ep93xx/timer.c

   1 /*
   2  * Cirrus Logic EP93xx timer support.
   3  *
   4  * Copyright (C) 2009, 2010 Matthias Kaehlcke <matthias@kaehlcke.net>
   5  *
   6  * Copyright (C) 2004, 2005
   7  * Cory T. Tusar, Videon Central, Inc., <ctusar@videon-central.com>
   8  *
   9  * Based on the original intr.c Cirrus Logic EP93xx Rev D. interrupt support,
  10  * author unknown.
  11  *
  12  * See file CREDITS for list of people who contributed to this project.
  13  *
  14  * This program is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU General Public License as published by
  16  * the Free Software Foundation; either version 2 of the License, or
  17  * (at your option) any later version.
  18  *
  19  * This program is distributed in the hope that it will be useful, but
  20  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  21  * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  22  * for more details.
  23  *
  24  * You should have received a copy of the GNU General Public License along
  25  * with this program; if not, write to the Free Software Foundation, Inc.,
  26  * 675 Mass Ave, Cambridge, MA 02139, USA.
  27  */
  28
  29 #include <common.h>
  30 #include <linux/types.h>
  31 #include <asm/arch/ep93xx.h>
  32 #include <asm/io.h>
  33 #include <div64.h>
  34
  35 #define TIMER_CLKSEL    (1 << 3)
  36 #define TIMER_ENABLE    (1 << 7)
  37
  38 #define TIMER_FREQ                      508469          /* ticks / second */
  39 #define TIMER_MAX_VAL                   0xFFFFFFFF
  40
  41 static struct ep93xx_timer
  42 {
  43         unsigned long long ticks;
  44         unsigned long last_read;
  45 } timer;
  46
  47 static inline unsigned long long usecs_to_ticks(unsigned long usecs)
  48 {
  49         unsigned long long ticks = (unsigned long long)usecs * TIMER_FREQ;
  50         do_div(ticks, 1000 * 1000);
  51
  52         return ticks;
  53 }
  54
  55 static inline void read_timer(void)
  56 {
  57         struct timer_regs *timer_regs = (struct timer_regs *)TIMER_BASE;
  58         const unsigned long now = TIMER_MAX_VAL - readl(&timer_regs->timer3.value);
  59
  60         if (now >= timer.last_read)
  61                 timer.ticks += now - timer.last_read;
  62         else
  63                 /* an overflow occurred */
  64                 timer.ticks += TIMER_MAX_VAL - timer.last_read + now;
  65
  66         timer.last_read = now;
  67 }
  68
  69 /*
  70  * Get the number of ticks (in CONFIG_SYS_HZ resolution)
  71  */
  72 unsigned long long get_ticks(void)
  73 {
  74         unsigned long long sys_ticks;
  75
  76         read_timer();
  77
  78         sys_ticks = timer.ticks * CONFIG_SYS_HZ;
  79         do_div(sys_ticks, TIMER_FREQ);
  80
  81         return sys_ticks;
  82 }
  83
  84 unsigned long get_timer_masked(void)
  85 {
  86         return get_ticks();
  87 }
  88
  89 unsigned long get_timer(unsigned long base)
  90 {
  91         return get_timer_masked() - base;
  92 }
  93
  94 void reset_timer_masked(void)
  95 {
  96         read_timer();
  97         timer.ticks = 0;
  98 }
  99
 100 void __udelay(unsigned long usec)
 101 {
 102         unsigned long long target;
 103
 104         read_timer();
 105
 106         target = timer.ticks + usecs_to_ticks(usec);
 107
 108         while (timer.ticks < target)
 109                 read_timer();
 110 }
 111
 112 int timer_init(void)
 113 {
 114         struct timer_regs *timer_regs = (struct timer_regs *)TIMER_BASE;
 115
 116         /* use timer 3 with 508KHz and free running, not enabled now */
 117         writel(TIMER_CLKSEL, &timer_regs->timer3.control);
 118
 119         /* set initial timer value */
 120         writel(TIMER_MAX_VAL, &timer_regs->timer3.load);
 121
 122         /* Enable the timer */
 123         writel(TIMER_ENABLE | TIMER_CLKSEL,
 124                 &timer_regs->timer3.control);
 125
 126         reset_timer_masked();
 127
 128         return 0;
 129 }
 130
 131 /*
 132  * This function is derived from PowerPC code (timebase clock frequency).
 133  * On ARM it returns the number of timer ticks per second.
 134  */
 135 unsigned long get_tbclk(void)
 136 {
 137         return CONFIG_SYS_HZ;
 138 }