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localtimer.c

/*
 *  linux/arch/arm/mach-realview/localtimer.c
 *
 *  Copyright (C) 2002 ARM Ltd.
 *  All Rights Reserved
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/smp.h>
#include <linux/jiffies.h>

#include <asm/mach/time.h>
#include <asm/hardware/arm_twd.h>
#include <asm/hardware/gic.h>
#include <asm/hardware.h>
#include <asm/io.h>
#include <asm/irq.h>

#define TWD_BASE(cpu)   (__io_address(REALVIEW_TWD_BASE) + \
                   ((cpu) * REALVIEW_TWD_SIZE))

static unsigned long mpcore_timer_rate;

/*
 * local_timer_ack: checks for a local timer interrupt.
 *
 * If a local timer interrupt has occured, acknowledge and return 1.
 * Otherwise, return 0.
 */
int local_timer_ack(void)
{
      void __iomem *base = TWD_BASE(smp_processor_id());

      if (__raw_readl(base + TWD_TIMER_INTSTAT)) {
            __raw_writel(1, base + TWD_TIMER_INTSTAT);
            return 1;
      }

      return 0;
}

void __cpuinit local_timer_setup(unsigned int cpu)
{
      void __iomem *base = TWD_BASE(cpu);
      unsigned int load, offset;
      u64 waitjiffies;
      unsigned int count;

      /*
       * If this is the first time round, we need to work out how fast
       * the timer ticks
       */
      if (mpcore_timer_rate == 0) {
            printk("Calibrating local timer... ");

            /* Wait for a tick to start */
            waitjiffies = get_jiffies_64() + 1;

            while (get_jiffies_64() < waitjiffies)
                  udelay(10);

            /* OK, now the tick has started, let's get the timer going */
            waitjiffies += 5;

                         /* enable, no interrupt or reload */
            __raw_writel(0x1, base + TWD_TIMER_CONTROL);

                         /* maximum value */
            __raw_writel(0xFFFFFFFFU, base + TWD_TIMER_COUNTER);

            while (get_jiffies_64() < waitjiffies)
                  udelay(10);

            count = __raw_readl(base + TWD_TIMER_COUNTER);

            mpcore_timer_rate = (0xFFFFFFFFU - count) * (HZ / 5);

            printk("%lu.%02luMHz.\n", mpcore_timer_rate / 1000000,
                  (mpcore_timer_rate / 100000) % 100);
      }

      load = mpcore_timer_rate / HZ;

      __raw_writel(load, base + TWD_TIMER_LOAD);
      __raw_writel(0x7,  base + TWD_TIMER_CONTROL);

      /*
       * Now maneuver our local tick into the right part of the jiffy.
       * Start by working out where within the tick our local timer
       * interrupt should go.
       */
      offset = ((mpcore_timer_rate / HZ) / (NR_CPUS + 1)) * (cpu + 1);

      /*
       * gettimeoffset() will return a number of us since the last tick.
       * Convert this number of us to a local timer tick count.
       * Be careful of integer overflow whilst keeping maximum precision.
       *
       * with HZ=100 and 1MHz (fpga) ~ 1GHz processor:
       * load = 1 ~ 10,000
       * mpcore_timer_rate/10000 = 100 ~ 100,000
       *
       * so the multiply value will be less than 10^9 always.
       */
      load = (system_timer->offset() * (mpcore_timer_rate / 10000)) / 100;

      /* Add on our offset to get the load value */
      load = (load + offset) % (mpcore_timer_rate / HZ);

      __raw_writel(load, base + TWD_TIMER_COUNTER);

      /* Make sure our local interrupt controller has this enabled */
      __raw_writel(1 << IRQ_LOCALTIMER,
                 __io_address(REALVIEW_GIC_DIST_BASE) + GIC_DIST_ENABLE_SET);
}

/*
 * take a local timer down
 */
void __cpuexit local_timer_stop(unsigned int cpu)
{
      __raw_writel(0, TWD_BASE(cpu) + TWD_TIMER_CONTROL);
}

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