arch/arm/include/asm/arch_timer.h

#ifndef __ASMARM_ARCH_TIMER_H
#define __ASMARM_ARCH_TIMER_H

#include <asm/barrier.h>
#include <asm/errno.h>
#include <linux/clocksource.h>
#include <linux/types.h>

#ifdef CONFIG_ARM_ARCH_TIMER
int arch_timer_of_register(void);
int arch_timer_sched_clock_init(void);
struct timecounter *arch_timer_get_timecounter(void);

#define ARCH_TIMER_CTRL_ENABLE		(1 << 0)
#define ARCH_TIMER_CTRL_IT_MASK		(1 << 1)
#define ARCH_TIMER_CTRL_IT_STAT		(1 << 2)

#define ARCH_TIMER_REG_CTRL		0
#define ARCH_TIMER_REG_TVAL		1

#define ARCH_TIMER_PHYS_ACCESS		0
#define ARCH_TIMER_VIRT_ACCESS		1

/*
 * These register accessors are marked inline so the compiler can
 * nicely work out which register we want, and chuck away the rest of
 * the code. At least it does so with a recent GCC (4.6.3).
 */
static inline void arch_timer_reg_write(const int access, const int reg, u32 val)
{
	if (access == ARCH_TIMER_PHYS_ACCESS) {
		switch (reg) {
		case ARCH_TIMER_REG_CTRL:
			asm volatile("mcr p15, 0, %0, c14, c2, 1" : : "r" (val));
			break;
		case ARCH_TIMER_REG_TVAL:
			asm volatile("mcr p15, 0, %0, c14, c2, 0" : : "r" (val));
			break;
		}
	}

	if (access == ARCH_TIMER_VIRT_ACCESS) {
		switch (reg) {
		case ARCH_TIMER_REG_CTRL:
			asm volatile("mcr p15, 0, %0, c14, c3, 1" : : "r" (val));
			break;
		case ARCH_TIMER_REG_TVAL:
			asm volatile("mcr p15, 0, %0, c14, c3, 0" : : "r" (val));
			break;
		}
	}
}

static inline u32 arch_timer_reg_read(const int access, const int reg)
{
	u32 val = 0;

	if (access == ARCH_TIMER_PHYS_ACCESS) {
		switch (reg) {
		case ARCH_TIMER_REG_CTRL:
			asm volatile("mrc p15, 0, %0, c14, c2, 1" : "=r" (val));
			break;
		case ARCH_TIMER_REG_TVAL:
			asm volatile("mrc p15, 0, %0, c14, c2, 0" : "=r" (val));
			break;
		}
	}

	if (access == ARCH_TIMER_VIRT_ACCESS) {
		switch (reg) {
		case ARCH_TIMER_REG_CTRL:
			asm volatile("mrc p15, 0, %0, c14, c3, 1" : "=r" (val));
			break;
		case ARCH_TIMER_REG_TVAL:
			asm volatile("mrc p15, 0, %0, c14, c3, 0" : "=r" (val));
			break;
		}
	}

	return val;
}

static inline u32 arch_timer_get_cntfrq(void)
{
	u32 val;
	asm volatile("mrc p15, 0, %0, c14, c0, 0" : "=r" (val));
	return val;
}

static inline u64 arch_counter_get_cntpct(void)
{
	u64 cval;

	asm volatile("mrrc p15, 0, %Q0, %R0, c14" : "=r" (cval));
	return cval;
}

static inline u64 arch_counter_get_cntvct(void)
{
	u64 cval;

	asm volatile("mrrc p15, 1, %Q0, %R0, c14" : "=r" (cval));
	return cval;
}
#else
static inline int arch_timer_of_register(void)
{
	return -ENXIO;
}

static inline int arch_timer_sched_clock_init(void)
{
	return -ENXIO;
}

static inline struct timecounter *arch_timer_get_timecounter(void)
{
	return NULL;
}
#endif

#endif