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  * SPDX-License-Identifier:     GPL-2.0+
  13  */
  14
  15 #include <common.h>
  16 #include <linux/types.h>
  17 #include <asm/arch/ep93xx.h>
  18 #include <asm/io.h>
  19 #include <div64.h>
  20
  21 #define TIMER_CLKSEL    (1 << 3)
  22 #define TIMER_ENABLE    (1 << 7)
  23
  24 #define TIMER_FREQ                      508469          /* ticks / second */
  25 #define TIMER_MAX_VAL                   0xFFFFFFFF
  26
  27 static struct ep93xx_timer
  28 {
  29         unsigned long long ticks;
  30         unsigned long last_read;
  31 } timer;
  32
  33 static inline unsigned long long usecs_to_ticks(unsigned long usecs)
  34 {
  35         unsigned long long ticks = (unsigned long long)usecs * TIMER_FREQ;
  36         do_div(ticks, 1000 * 1000);
  37
  38         return ticks;
  39 }
  40
  41 static inline void read_timer(void)
  42 {
  43         struct timer_regs *timer_regs = (struct timer_regs *)TIMER_BASE;
  44         const unsigned long now = TIMER_MAX_VAL - readl(&timer_regs->timer3.value);
  45
  46         if (now >= timer.last_read)
  47                 timer.ticks += now - timer.last_read;
  48         else
  49                 /* an overflow occurred */
  50                 timer.ticks += TIMER_MAX_VAL - timer.last_read + now;
  51
  52         timer.last_read = now;
  53 }
  54
  55 /*
  56  * Get the number of ticks (in CONFIG_SYS_HZ resolution)
  57  */
  58 unsigned long long get_ticks(void)
  59 {
  60         unsigned long long sys_ticks;
  61
  62         read_timer();
  63
  64         sys_ticks = timer.ticks * CONFIG_SYS_HZ;
  65         do_div(sys_ticks, TIMER_FREQ);
  66
  67         return sys_ticks;
  68 }
  69
  70 unsigned long get_timer_masked(void)
  71 {
  72         return get_ticks();
  73 }
  74
  75 unsigned long get_timer(unsigned long base)
  76 {
  77         return get_timer_masked() - base;
  78 }
  79
  80 void __udelay(unsigned long usec)
  81 {
  82         unsigned long long target;
  83
  84         read_timer();
  85
  86         target = timer.ticks + usecs_to_ticks(usec);
  87
  88         while (timer.ticks < target)
  89                 read_timer();
  90 }
  91
  92 int timer_init(void)
  93 {
  94         struct timer_regs *timer_regs = (struct timer_regs *)TIMER_BASE;
  95
  96         /* use timer 3 with 508KHz and free running, not enabled now */
  97         writel(TIMER_CLKSEL, &timer_regs->timer3.control);
  98
  99         /* set initial timer value */
 100         writel(TIMER_MAX_VAL, &timer_regs->timer3.load);
 101
 102         /* Enable the timer */
 103         writel(TIMER_ENABLE | TIMER_CLKSEL,
 104                 &timer_regs->timer3.control);
 105
 106         /* Reset the timer */
 107         read_timer();
 108         timer.ticks = 0;
 109
 110         return 0;
 111 }
 112
 113 /*
 114  * This function is derived from PowerPC code (timebase clock frequency).
 115  * On ARM it returns the number of timer ticks per second.
 116  */
 117 unsigned long get_tbclk(void)
 118 {
 119         return CONFIG_SYS_HZ;
 120 }