linux/drivers/clocksource/clksrc-dbx500-prcmu.c
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   1/*
   2 * Copyright (C) ST-Ericsson SA 2011
   3 *
   4 * License Terms: GNU General Public License v2
   5 * Author: Mattias Wallin <mattias.wallin@stericsson.com> for ST-Ericsson
   6 * Author: Sundar Iyer for ST-Ericsson
   7 * sched_clock implementation is based on:
   8 * plat-nomadik/timer.c Linus Walleij <linus.walleij@stericsson.com>
   9 *
  10 * DBx500-PRCMU Timer
  11 * The PRCMU has 5 timers which are available in a always-on
  12 * power domain.  We use the Timer 4 for our always-on clock
  13 * source on DB8500 and Timer 3 on DB5500.
  14 */
  15#include <linux/clockchips.h>
  16#include <linux/clksrc-dbx500-prcmu.h>
  17
  18#include <asm/sched_clock.h>
  19
  20#include <mach/setup.h>
  21#include <mach/hardware.h>
  22
  23#define RATE_32K                32768
  24
  25#define TIMER_MODE_CONTINOUS    0x1
  26#define TIMER_DOWNCOUNT_VAL     0xffffffff
  27
  28#define PRCMU_TIMER_REF         0
  29#define PRCMU_TIMER_DOWNCOUNT   0x4
  30#define PRCMU_TIMER_MODE        0x8
  31
  32#define SCHED_CLOCK_MIN_WRAP 131072 /* 2^32 / 32768 */
  33
  34static void __iomem *clksrc_dbx500_timer_base;
  35
  36static cycle_t clksrc_dbx500_prcmu_read(struct clocksource *cs)
  37{
  38        u32 count, count2;
  39
  40        do {
  41                count = readl(clksrc_dbx500_timer_base +
  42                              PRCMU_TIMER_DOWNCOUNT);
  43                count2 = readl(clksrc_dbx500_timer_base +
  44                               PRCMU_TIMER_DOWNCOUNT);
  45        } while (count2 != count);
  46
  47        /* Negate because the timer is a decrementing counter */
  48        return ~count;
  49}
  50
  51static struct clocksource clocksource_dbx500_prcmu = {
  52        .name           = "dbx500-prcmu-timer",
  53        .rating         = 300,
  54        .read           = clksrc_dbx500_prcmu_read,
  55        .mask           = CLOCKSOURCE_MASK(32),
  56        .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
  57};
  58
  59#ifdef CONFIG_CLKSRC_DBX500_PRCMU_SCHED_CLOCK
  60
  61static u32 notrace dbx500_prcmu_sched_clock_read(void)
  62{
  63        if (unlikely(!clksrc_dbx500_timer_base))
  64                return 0;
  65
  66        return clksrc_dbx500_prcmu_read(&clocksource_dbx500_prcmu);
  67}
  68
  69#endif
  70
  71void __init clksrc_dbx500_prcmu_init(void __iomem *base)
  72{
  73        clksrc_dbx500_timer_base = base;
  74
  75        /*
  76         * The A9 sub system expects the timer to be configured as
  77         * a continous looping timer.
  78         * The PRCMU should configure it but if it for some reason
  79         * don't we do it here.
  80         */
  81        if (readl(clksrc_dbx500_timer_base + PRCMU_TIMER_MODE) !=
  82            TIMER_MODE_CONTINOUS) {
  83                writel(TIMER_MODE_CONTINOUS,
  84                       clksrc_dbx500_timer_base + PRCMU_TIMER_MODE);
  85                writel(TIMER_DOWNCOUNT_VAL,
  86                       clksrc_dbx500_timer_base + PRCMU_TIMER_REF);
  87        }
  88#ifdef CONFIG_CLKSRC_DBX500_PRCMU_SCHED_CLOCK
  89        setup_sched_clock(dbx500_prcmu_sched_clock_read,
  90                         32, RATE_32K);
  91#endif
  92        clocksource_register_hz(&clocksource_dbx500_prcmu, RATE_32K);
  93}
  94
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