drivers/clocksource/arm_global_timer.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * 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>
  */

 #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/delay.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_CONTROL_PRESCALER_SHIFT      8
 #define GT_CONTROL_PRESCALER_MAX        0xF
 #define GT_CONTROL_PRESCALER_MASK       (GT_CONTROL_PRESCALER_MAX << \
 					 GT_CONTROL_PRESCALER_SHIFT)

 #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

 #define MAX_F_ERR 50
 /*
  * 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 struct notifier_block gt_clk_rate_change_nb;
 static u32 gt_psv_new, gt_psv_bck, gt_target_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 = readl(gt_base + GT_CONTROL);
 	ctrl &= ~(GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE |
 		  GT_CONTROL_AUTO_INC);
 	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_target_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_starting_cpu(unsigned int cpu)
 {
 	struct clock_event_device *clk = this_cpu_ptr(gt_evt);

 	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_state_oneshot_stopped = 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_target_rate,
 					1, 0xffffffff);
 	enable_percpu_irq(clk->irq, IRQ_TYPE_NONE);
 	return 0;
 }

 static int gt_dying_cpu(unsigned int cpu)
 {
 	struct clock_event_device *clk = this_cpu_ptr(gt_evt);

 	gt_clockevent_shutdown(clk);
 	disable_percpu_irq(clk->irq);
 	return 0;
 }

 static u64 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 unsigned long gt_read_long(void)
 {
 	return readl_relaxed(gt_base + GT_COUNTER0);
 }

 static struct delay_timer gt_delay_timer = {
 	.read_current_timer = gt_read_long,
 };

 static void gt_write_presc(u32 psv)
 {
 	u32 reg;

 	reg = readl(gt_base + GT_CONTROL);
 	reg &= ~GT_CONTROL_PRESCALER_MASK;
 	reg |= psv << GT_CONTROL_PRESCALER_SHIFT;
 	writel(reg, gt_base + GT_CONTROL);
 }

 static u32 gt_read_presc(void)
 {
 	u32 reg;

 	reg = readl(gt_base + GT_CONTROL);
 	reg &= GT_CONTROL_PRESCALER_MASK;
 	return reg >> GT_CONTROL_PRESCALER_SHIFT;
 }

 static void __init gt_delay_timer_init(void)
 {
 	gt_delay_timer.freq = gt_target_rate;
 	register_current_timer_delay(&gt_delay_timer);
 }

 static int __init gt_clocksource_init(void)
 {
 	writel(0, gt_base + GT_CONTROL);
 	writel(0, gt_base + GT_COUNTER0);
 	writel(0, gt_base + GT_COUNTER1);
 	/* set prescaler and enable timer on all the cores */
 	writel(((CONFIG_ARM_GT_INITIAL_PRESCALER_VAL - 1) <<
 		GT_CONTROL_PRESCALER_SHIFT)
 	       | 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_target_rate);
 #endif
 	return clocksource_register_hz(&gt_clocksource, gt_target_rate);
 }

 static int gt_clk_rate_change_cb(struct notifier_block *nb,
 				 unsigned long event, void *data)
 {
 	struct clk_notifier_data *ndata = data;

 	switch (event) {
 	case PRE_RATE_CHANGE:
 	{
 		int psv;

 		psv = DIV_ROUND_CLOSEST(ndata->new_rate,
 					gt_target_rate);

 		if (abs(gt_target_rate - (ndata->new_rate / psv)) > MAX_F_ERR)
 			return NOTIFY_BAD;

 		psv--;

 		/* prescaler within legal range? */
 		if (psv < 0 || psv > GT_CONTROL_PRESCALER_MAX)
 			return NOTIFY_BAD;

 		/*
 		 * store timer clock ctrl register so we can restore it in case
 		 * of an abort.
 		 */
 		gt_psv_bck = gt_read_presc();
 		gt_psv_new = psv;
 		/* scale down: adjust divider in post-change notification */
 		if (ndata->new_rate < ndata->old_rate)
 			return NOTIFY_DONE;

 		/* scale up: adjust divider now - before frequency change */
 		gt_write_presc(psv);
 		break;
 	}
 	case POST_RATE_CHANGE:
 		/* scale up: pre-change notification did the adjustment */
 		if (ndata->new_rate > ndata->old_rate)
 			return NOTIFY_OK;

 		/* scale down: adjust divider now - after frequency change */
 		gt_write_presc(gt_psv_new);
 		break;

 	case ABORT_RATE_CHANGE:
 		/* we have to undo the adjustment in case we scale up */
 		if (ndata->new_rate < ndata->old_rate)
 			return NOTIFY_OK;

 		/* restore original register value */
 		gt_write_presc(gt_psv_bck);
 		break;
 	default:
 		return NOTIFY_DONE;
 	}

 	return NOTIFY_DONE;
 }

 static int __init global_timer_of_register(struct device_node *np)
 {
 	struct clk *gt_clk;
 	static unsigned long gt_clk_rate;
 	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 -ENOSYS;
 	}

 	gt_ppi = irq_of_parse_and_map(np, 0);
 	if (!gt_ppi) {
 		pr_warn("global-timer: unable to parse irq\n");
 		return -EINVAL;
 	}

 	gt_base = of_iomap(np, 0);
 	if (!gt_base) {
 		pr_warn("global-timer: invalid base address\n");
 		return -ENXIO;
 	}

 	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_target_rate = gt_clk_rate / CONFIG_ARM_GT_INITIAL_PRESCALER_VAL;
 	gt_clk_rate_change_nb.notifier_call =
 		gt_clk_rate_change_cb;
 	err = clk_notifier_register(gt_clk, &gt_clk_rate_change_nb);
 	if (err) {
 		pr_warn("Unable to register clock notifier\n");
 		goto out_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_nb;
 	}

 	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;
 	}

 	/* Register and immediately configure the timer on the boot CPU */
 	err = gt_clocksource_init();
 	if (err)
 		goto out_irq;

 	err = cpuhp_setup_state(CPUHP_AP_ARM_GLOBAL_TIMER_STARTING,
 				"clockevents/arm/global_timer:starting",
 				gt_starting_cpu, gt_dying_cpu);
 	if (err)
 		goto out_irq;

 	gt_delay_timer_init();

 	return 0;

 out_irq:
 	free_percpu_irq(gt_ppi, gt_evt);
 out_free:
 	free_percpu(gt_evt);
 out_clk_nb:
 	clk_notifier_unregister(gt_clk, &gt_clk_rate_change_nb);
 out_clk:
 	clk_disable_unprepare(gt_clk);
 out_unmap:
 	iounmap(gt_base);
 	WARN(err, "ARM Global timer register failed (%d)\n", err);

 	return err;
 }

 /* Only tested on r2p2 and r3p0  */
 TIMER_OF_DECLARE(arm_gt, "arm,cortex-a9-global-timer",
 			global_timer_of_register);
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* 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>
	*/

	#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/delay.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_CONTROL_PRESCALER_SHIFT 8
	#define GT_CONTROL_PRESCALER_MAX 0xF
	#define GT_CONTROL_PRESCALER_MASK (GT_CONTROL_PRESCALER_MAX << \
	GT_CONTROL_PRESCALER_SHIFT)

	#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

	#define MAX_F_ERR 50
	/*
	* 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 struct notifier_block gt_clk_rate_change_nb;
	static u32 gt_psv_new, gt_psv_bck, gt_target_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 = readl(gt_base + GT_CONTROL);
	ctrl &= ~(GT_CONTROL_COMP_ENABLE \| GT_CONTROL_IRQ_ENABLE \|
	GT_CONTROL_AUTO_INC);
	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_target_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_starting_cpu(unsigned int cpu)
	{
	struct clock_event_device *clk = this_cpu_ptr(gt_evt);

	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_state_oneshot_stopped = 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_target_rate,
	1, 0xffffffff);
	enable_percpu_irq(clk->irq, IRQ_TYPE_NONE);
	return 0;
	}

	static int gt_dying_cpu(unsigned int cpu)
	{
	struct clock_event_device *clk = this_cpu_ptr(gt_evt);

	gt_clockevent_shutdown(clk);
	disable_percpu_irq(clk->irq);
	return 0;
	}

	static u64 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 unsigned long gt_read_long(void)
	{
	return readl_relaxed(gt_base + GT_COUNTER0);
	}

	static struct delay_timer gt_delay_timer = {
	.read_current_timer = gt_read_long,
	};

	static void gt_write_presc(u32 psv)
	{
	u32 reg;

	reg = readl(gt_base + GT_CONTROL);
	reg &= ~GT_CONTROL_PRESCALER_MASK;
	reg \|= psv << GT_CONTROL_PRESCALER_SHIFT;
	writel(reg, gt_base + GT_CONTROL);
	}

	static u32 gt_read_presc(void)
	{
	u32 reg;

	reg = readl(gt_base + GT_CONTROL);
	reg &= GT_CONTROL_PRESCALER_MASK;
	return reg >> GT_CONTROL_PRESCALER_SHIFT;
	}

	static void __init gt_delay_timer_init(void)
	{
	gt_delay_timer.freq = gt_target_rate;
	register_current_timer_delay(&gt_delay_timer);
	}

	static int __init gt_clocksource_init(void)
	{
	writel(0, gt_base + GT_CONTROL);
	writel(0, gt_base + GT_COUNTER0);
	writel(0, gt_base + GT_COUNTER1);
	/* set prescaler and enable timer on all the cores */
	writel(((CONFIG_ARM_GT_INITIAL_PRESCALER_VAL - 1) <<
	GT_CONTROL_PRESCALER_SHIFT)
	\| 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_target_rate);
	#endif
	return clocksource_register_hz(&gt_clocksource, gt_target_rate);
	}

	static int gt_clk_rate_change_cb(struct notifier_block *nb,
	unsigned long event, void *data)
	{
	struct clk_notifier_data *ndata = data;

	switch (event) {
	case PRE_RATE_CHANGE:
	{
	int psv;

	psv = DIV_ROUND_CLOSEST(ndata->new_rate,
	gt_target_rate);

	if (abs(gt_target_rate - (ndata->new_rate / psv)) > MAX_F_ERR)
	return NOTIFY_BAD;

	psv--;

	/* prescaler within legal range? */
	if (psv < 0 \|\| psv > GT_CONTROL_PRESCALER_MAX)
	return NOTIFY_BAD;

	/*
	* store timer clock ctrl register so we can restore it in case
	* of an abort.
	*/
	gt_psv_bck = gt_read_presc();
	gt_psv_new = psv;
	/* scale down: adjust divider in post-change notification */
	if (ndata->new_rate < ndata->old_rate)
	return NOTIFY_DONE;

	/* scale up: adjust divider now - before frequency change */
	gt_write_presc(psv);
	break;
	}
	case POST_RATE_CHANGE:
	/* scale up: pre-change notification did the adjustment */
	if (ndata->new_rate > ndata->old_rate)
	return NOTIFY_OK;

	/* scale down: adjust divider now - after frequency change */
	gt_write_presc(gt_psv_new);
	break;

	case ABORT_RATE_CHANGE:
	/* we have to undo the adjustment in case we scale up */
	if (ndata->new_rate < ndata->old_rate)
	return NOTIFY_OK;

	/* restore original register value */
	gt_write_presc(gt_psv_bck);
	break;
	default:
	return NOTIFY_DONE;
	}

	return NOTIFY_DONE;
	}

	static int __init global_timer_of_register(struct device_node *np)
	{
	struct clk *gt_clk;
	static unsigned long gt_clk_rate;
	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 -ENOSYS;
	}

	gt_ppi = irq_of_parse_and_map(np, 0);
	if (!gt_ppi) {
	pr_warn("global-timer: unable to parse irq\n");
	return -EINVAL;
	}

	gt_base = of_iomap(np, 0);
	if (!gt_base) {
	pr_warn("global-timer: invalid base address\n");
	return -ENXIO;
	}

	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_target_rate = gt_clk_rate / CONFIG_ARM_GT_INITIAL_PRESCALER_VAL;
	gt_clk_rate_change_nb.notifier_call =
	gt_clk_rate_change_cb;
	err = clk_notifier_register(gt_clk, &gt_clk_rate_change_nb);
	if (err) {
	pr_warn("Unable to register clock notifier\n");
	goto out_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_nb;
	}

	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;
	}

	/* Register and immediately configure the timer on the boot CPU */
	err = gt_clocksource_init();
	if (err)
	goto out_irq;

	err = cpuhp_setup_state(CPUHP_AP_ARM_GLOBAL_TIMER_STARTING,
	"clockevents/arm/global_timer:starting",
	gt_starting_cpu, gt_dying_cpu);
	if (err)
	goto out_irq;

	gt_delay_timer_init();

	return 0;

	out_irq:
	free_percpu_irq(gt_ppi, gt_evt);
	out_free:
	free_percpu(gt_evt);
	out_clk_nb:
	clk_notifier_unregister(gt_clk, &gt_clk_rate_change_nb);
	out_clk:
	clk_disable_unprepare(gt_clk);
	out_unmap:
	iounmap(gt_base);
	WARN(err, "ARM Global timer register failed (%d)\n", err);

	return err;
	}

	/* Only tested on r2p2 and r3p0 */
	TIMER_OF_DECLARE(arm_gt, "arm,cortex-a9-global-timer",
	global_timer_of_register);