text: /*
   * drivers/clocksource/arm_global_timer.c
   *
   * Copyright (C) 2013 STMicroelectronics (R&D) Limited.
   * Author: Stuart Menefy <stuart.menefy@st.com>
   * Author: Srinivas Kandagatla <srinivas.kandagatla@st.com>
   *
   * 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/interrupt.h>
  #include <linux/clocksource.h>
  #include <linux/clockchips.h>
  #include <linux/cpu.h>
  #include <linux/clk.h>
  #include <linux/err.h>
  #include <linux/io.h>
  #include <linux/of.h>
  #include <linux/of_irq.h>
  #include <linux/of_address.h>
  #include <linux/sched_clock.h>
  
  #include <asm/cputype.h>
  
  #define GT_COUNTER0	0x00
  #define GT_COUNTER1	0x04
  
  #define GT_CONTROL	0x08
  #define GT_CONTROL_TIMER_ENABLE		BIT(0)  /* this bit is NOT banked */
  #define GT_CONTROL_COMP_ENABLE		BIT(1)	/* banked */
  #define GT_CONTROL_IRQ_ENABLE		BIT(2)	/* banked */
  #define GT_CONTROL_AUTO_INC		BIT(3)	/* banked */
  
  #define GT_INT_STATUS	0x0c
  #define GT_INT_STATUS_EVENT_FLAG	BIT(0)
  
  #define GT_COMP0	0x10
  #define GT_COMP1	0x14
  #define GT_AUTO_INC	0x18
  
  /*
   * We are expecting to be clocked by the ARM peripheral clock.
   *
   * Note: it is assumed we are using a prescaler value of zero, so this is
   * the units for all operations.
   */
  static void __iomem *gt_base;
  static unsigned long gt_clk_rate;
  static int gt_ppi;
  static struct clock_event_device __percpu *gt_evt;
  
  /*
   * To get the value from the Global Timer Counter register proceed as follows:
   * 1. Read the upper 32-bit timer counter register
   * 2. Read the lower 32-bit timer counter register
   * 3. Read the upper 32-bit timer counter register again. If the value is
   *  different to the 32-bit upper value read previously, go back to step 2.
   *  Otherwise the 64-bit timer counter value is correct.
   */
  static u64 notrace _gt_counter_read(void)
  {
  	u64 counter;
  	u32 lower;
  	u32 upper, old_upper;
  
  	upper = readl_relaxed(gt_base + GT_COUNTER1);
  	do {
  		old_upper = upper;
  		lower = readl_relaxed(gt_base + GT_COUNTER0);
  		upper = readl_relaxed(gt_base + GT_COUNTER1);
  	} while (upper != old_upper);
  
  	counter = upper;
  	counter <<= 32;
  	counter |= lower;
  	return counter;
  }
  
  static u64 gt_counter_read(void)
  {
  	return _gt_counter_read();
  }
  
  /**
   * To ensure that updates to comparator value register do not set the
   * Interrupt Status Register proceed as follows:
   * 1. Clear the Comp Enable bit in the Timer Control Register.
   * 2. Write the lower 32-bit Comparator Value Register.
   * 3. Write the upper 32-bit Comparator Value Register.
   * 4. Set the Comp Enable bit and, if necessary, the IRQ enable bit.
   */
  static void gt_compare_set(unsigned long delta, int periodic)
  {
  	u64 counter = gt_counter_read();
  	unsigned long ctrl;
  
  	counter += delta;
  	ctrl = GT_CONTROL_TIMER_ENABLE;
  	writel_relaxed(ctrl, gt_base + GT_CONTROL);
  	writel_relaxed(lower_32_bits(counter), gt_base + GT_COMP0);
  	writel_relaxed(upper_32_bits(counter), gt_base + GT_COMP1);
  
  	if (periodic) {
  		writel_relaxed(delta, gt_base + GT_AUTO_INC);
  		ctrl |= GT_CONTROL_AUTO_INC;
  	}
  
  	ctrl |= GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE;
  	writel_relaxed(ctrl, gt_base + GT_CONTROL);
  }
  
  static int gt_clockevent_shutdown(struct clock_event_device *evt)
  {
  	unsigned long ctrl;
  
  	ctrl = readl(gt_base + GT_CONTROL);
  	ctrl &= ~(GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE |
  		  GT_CONTROL_AUTO_INC);
  	writel(ctrl, gt_base + GT_CONTROL);
  	return 0;
  }
  
  static int gt_clockevent_set_periodic(struct clock_event_device *evt)
  {
  	gt_compare_set(DIV_ROUND_CLOSEST(gt_clk_rate, HZ), 1);
  	return 0;
  }
  
  static int gt_clockevent_set_next_event(unsigned long evt,
  					struct clock_event_device *unused)
  {
  	gt_compare_set(evt, 0);
  	return 0;
  }
  
  static irqreturn_t gt_clockevent_interrupt(int irq, void *dev_id)
  {
  	struct clock_event_device *evt = dev_id;
  
  	if (!(readl_relaxed(gt_base + GT_INT_STATUS) &
  				GT_INT_STATUS_EVENT_FLAG))
  		return IRQ_NONE;
  
  	/**
  	 * ERRATA 740657( Global Timer can send 2 interrupts for
  	 * the same event in single-shot mode)
  	 * Workaround:
  	 *	Either disable single-shot mode.
  	 *	Or
  	 *	Modify the Interrupt Handler to avoid the
  	 *	offending sequence. This is achieved by clearing
  	 *	the Global Timer flag _after_ having incremented
  	 *	the Comparator register	value to a higher value.
  	 */
  	if (clockevent_state_oneshot(evt))
  		gt_compare_set(ULONG_MAX, 0);
  
  	writel_relaxed(GT_INT_STATUS_EVENT_FLAG, gt_base + GT_INT_STATUS);
  	evt->event_handler(evt);
  
  	return IRQ_HANDLED;
  }
  
  static int gt_clockevents_init(struct clock_event_device *clk)
  {
  	int cpu = smp_processor_id();
  
  	clk->name = "arm_global_timer";
  	clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
  		CLOCK_EVT_FEAT_PERCPU;
  	clk->set_state_shutdown = gt_clockevent_shutdown;
  	clk->set_state_periodic = gt_clockevent_set_periodic;
  	clk->set_state_oneshot = gt_clockevent_shutdown;
  	clk->set_next_event = gt_clockevent_set_next_event;
  	clk->cpumask = cpumask_of(cpu);
  	clk->rating = 300;
  	clk->irq = gt_ppi;
  	clockevents_config_and_register(clk, gt_clk_rate,
  					1, 0xffffffff);
  	enable_percpu_irq(clk->irq, IRQ_TYPE_NONE);
  	return 0;
  }
  
  static void gt_clockevents_stop(struct clock_event_device *clk)
  {
  	gt_clockevent_shutdown(clk);
  	disable_percpu_irq(clk->irq);
  }
  
  static cycle_t gt_clocksource_read(struct clocksource *cs)
  {
  	return gt_counter_read();
  }
  
  static void gt_resume(struct clocksource *cs)
  {
  	unsigned long ctrl;
  
  	ctrl = readl(gt_base + GT_CONTROL);
  	if (!(ctrl & GT_CONTROL_TIMER_ENABLE))
  		/* re-enable timer on resume */
  		writel(GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
  }
  
  static struct clocksource gt_clocksource = {
  	.name	= "arm_global_timer",
  	.rating	= 300,
  	.read	= gt_clocksource_read,
  	.mask	= CLOCKSOURCE_MASK(64),
  	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
  	.resume = gt_resume,
  };
  
  #ifdef CONFIG_CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
  static u64 notrace gt_sched_clock_read(void)
  {
  	return _gt_counter_read();
  }
  #endif
  
  static void __init gt_clocksource_init(void)
  {
  	writel(0, gt_base + GT_CONTROL);
  	writel(0, gt_base + GT_COUNTER0);
  	writel(0, gt_base + GT_COUNTER1);
  	/* enables timer on all the cores */
  	writel(GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
  
  #ifdef CONFIG_CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
  	sched_clock_register(gt_sched_clock_read, 64, gt_clk_rate);
  #endif
  	clocksource_register_hz(&gt_clocksource, gt_clk_rate);
  }
  
  static int gt_cpu_notify(struct notifier_block *self, unsigned long action,
  			 void *hcpu)
  {
  	switch (action & ~CPU_TASKS_FROZEN) {
  	case CPU_STARTING:
  		gt_clockevents_init(this_cpu_ptr(gt_evt));
  		break;
  	case CPU_DYING:
  		gt_clockevents_stop(this_cpu_ptr(gt_evt));
  		break;
  	}
  
  	return NOTIFY_OK;
  }
  static struct notifier_block gt_cpu_nb = {
  	.notifier_call = gt_cpu_notify,
  };
  
  static void __init global_timer_of_register(struct device_node *np)
  {
  	struct clk *gt_clk;
  	int err = 0;
  
  	/*
  	 * In A9 r2p0 the comparators for each processor with the global timer
  	 * fire when the timer value is greater than or equal to. In previous
  	 * revisions the comparators fired when the timer value was equal to.
  	 */
  	if (read_cpuid_part() == ARM_CPU_PART_CORTEX_A9
  	    && (read_cpuid_id() & 0xf0000f) < 0x200000) {
  		pr_warn("global-timer: non support for this cpu version.\n");
  		return;
  	}
  
  	gt_ppi = irq_of_parse_and_map(np, 0);
  	if (!gt_ppi) {
  		pr_warn("global-timer: unable to parse irq\n");
  		return;
  	}
  
  	gt_base = of_iomap(np, 0);
  	if (!gt_base) {
  		pr_warn("global-timer: invalid base address\n");
  		return;
  	}
  
  	gt_clk = of_clk_get(np, 0);
  	if (!IS_ERR(gt_clk)) {
  		err = clk_prepare_enable(gt_clk);
  		if (err)
  			goto out_unmap;
  	} else {
  		pr_warn("global-timer: clk not found\n");
  		err = -EINVAL;
  		goto out_unmap;
  	}
  
  	gt_clk_rate = clk_get_rate(gt_clk);
  	gt_evt = alloc_percpu(struct clock_event_device);
  	if (!gt_evt) {
  		pr_warn("global-timer: can't allocate memory\n");
  		err = -ENOMEM;
  		goto out_clk;
  	}
  
  	err = request_percpu_irq(gt_ppi, gt_clockevent_interrupt,
  				 "gt", gt_evt);
  	if (err) {
  		pr_warn("global-timer: can't register interrupt %d (%d)\n",
  			gt_ppi, err);
  		goto out_free;
  	}
  
  	err = register_cpu_notifier(&gt_cpu_nb);
  	if (err) {
  		pr_warn("global-timer: unable to register cpu notifier.\n");
  		goto out_irq;
  	}
  
  	/* Immediately configure the timer on the boot CPU */
  	gt_clocksource_init();
  	gt_clockevents_init(this_cpu_ptr(gt_evt));
  
  	return;
  
  out_irq:
  	free_percpu_irq(gt_ppi, gt_evt);
  out_free:
  	free_percpu(gt_evt);
  out_clk:
  	clk_disable_unprepare(gt_clk);
  out_unmap:
  	iounmap(gt_base);
  	WARN(err, "ARM Global timer register failed (%d)\n", err);
  }
  
  /* Only tested on r2p2 and r3p0  */
  CLOCKSOURCE_OF_DECLARE(arm_gt, "arm,cortex-a9-global-timer",
  			global_timer_of_register);
  