text: /*
   *  linux/arch/arm/kernel/smp_twd.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 <linux/clockchips.h>
  #include <linux/irq.h>
  #include <linux/io.h>
  
  #include <asm/smp_twd.h>
  #include <asm/hardware/gic.h>
  
  /* set up by the platform code */
  void __iomem *twd_base;
  
  static unsigned long twd_timer_rate;
  
  static void twd_set_mode(enum clock_event_mode mode,
  			struct clock_event_device *clk)
  {
  	unsigned long ctrl;
  
  	switch (mode) {
  	case CLOCK_EVT_MODE_PERIODIC:
  		/* timer load already set up */
  		ctrl = TWD_TIMER_CONTROL_ENABLE | TWD_TIMER_CONTROL_IT_ENABLE
  			| TWD_TIMER_CONTROL_PERIODIC;
  		break;
  	case CLOCK_EVT_MODE_ONESHOT:
  		/* period set, and timer enabled in 'next_event' hook */
  		ctrl = TWD_TIMER_CONTROL_IT_ENABLE | TWD_TIMER_CONTROL_ONESHOT;
  		break;
  	case CLOCK_EVT_MODE_UNUSED:
  	case CLOCK_EVT_MODE_SHUTDOWN:
  	default:
  		ctrl = 0;
  	}
  
  	__raw_writel(ctrl, twd_base + TWD_TIMER_CONTROL);
  }
  
  static int twd_set_next_event(unsigned long evt,
  			struct clock_event_device *unused)
  {
  	unsigned long ctrl = __raw_readl(twd_base + TWD_TIMER_CONTROL);
  
  	ctrl |= TWD_TIMER_CONTROL_ENABLE;
  
  	__raw_writel(evt, twd_base + TWD_TIMER_COUNTER);
  	__raw_writel(ctrl, twd_base + TWD_TIMER_CONTROL);
  
  	return 0;
  }
  
  /*
   * local_timer_ack: checks for a local timer interrupt.
   *
   * If a local timer interrupt has occurred, acknowledge and return 1.
   * Otherwise, return 0.
   */
  int twd_timer_ack(void)
  {
  	if (__raw_readl(twd_base + TWD_TIMER_INTSTAT)) {
  		__raw_writel(1, twd_base + TWD_TIMER_INTSTAT);
  		return 1;
  	}
  
  	return 0;
  }
  
  static void __cpuinit twd_calibrate_rate(void)
  {
  	unsigned long load, count;
  	u64 waitjiffies;
  
  	/*
  	 * If this is the first time round, we need to work out how fast
  	 * the timer ticks
  	 */
  	if (twd_timer_rate == 0) {
  		printk(KERN_INFO "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, twd_base + TWD_TIMER_CONTROL);
  
  				 /* maximum value */
  		__raw_writel(0xFFFFFFFFU, twd_base + TWD_TIMER_COUNTER);
  
  		while (get_jiffies_64() < waitjiffies)
  			udelay(10);
  
  		count = __raw_readl(twd_base + TWD_TIMER_COUNTER);
  
  		twd_timer_rate = (0xFFFFFFFFU - count) * (HZ / 5);
  
  		printk("%lu.%02luMHz.\n", twd_timer_rate / 1000000,
  			(twd_timer_rate / 100000) % 100);
  	}
  
  	load = twd_timer_rate / HZ;
  
  	__raw_writel(load, twd_base + TWD_TIMER_LOAD);
  }
  
  /*
   * Setup the local clock events for a CPU.
   */
  void __cpuinit twd_timer_setup(struct clock_event_device *clk)
  {
  	unsigned long flags;
  
  	twd_calibrate_rate();
  
  	clk->name = "local_timer";
  	clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
  			CLOCK_EVT_FEAT_C3STOP;
  	clk->rating = 350;
  	clk->set_mode = twd_set_mode;
  	clk->set_next_event = twd_set_next_event;
  	clk->shift = 20;
  	clk->mult = div_sc(twd_timer_rate, NSEC_PER_SEC, clk->shift);
  	clk->max_delta_ns = clockevent_delta2ns(0xffffffff, clk);
  	clk->min_delta_ns = clockevent_delta2ns(0xf, clk);
  
  	/* Make sure our local interrupt controller has this enabled */
  	local_irq_save(flags);
  	irq_to_desc(clk->irq)->status |= IRQ_NOPROBE;
  	get_irq_chip(clk->irq)->unmask(clk->irq);
  	local_irq_restore(flags);
  
  	clockevents_register_device(clk);
  }
  
  #ifdef CONFIG_HOTPLUG_CPU
  /*
   * take a local timer down
   */
  void twd_timer_stop(void)
  {
  	__raw_writel(0, twd_base + TWD_TIMER_CONTROL);
  }
  #endif
  