original_kernel/include/asm-powerpc/timex.h

#ifndef _ASM_POWERPC_TIMEX_H
#define _ASM_POWERPC_TIMEX_H

#ifdef __KERNEL__

/*
 * PowerPC architecture timex specifications
 */

#include <linux/config.h>
#include <asm/cputable.h>

#define CLOCK_TICK_RATE	1024000 /* Underlying HZ */

typedef unsigned long cycles_t;

static inline cycles_t get_cycles(void)
{
	cycles_t ret;

#ifdef __powerpc64__

	__asm__ __volatile__("mftb %0" : "=r" (ret) : );

#else
	/*
	 * For the "cycle" counter we use the timebase lower half.
	 * Currently only used on SMP.
	 */

	ret = 0;

	__asm__ __volatile__(
		"98:	mftb %0\n"
		"99:\n"
		".section __ftr_fixup,\"a\"\n"
		"	.long %1\n"
		"	.long 0\n"
		"	.long 98b\n"
		"	.long 99b\n"
		".previous"
		: "=r" (ret) : "i" (CPU_FTR_601));
#endif

	return ret;
}

#endif	/* __KERNEL__ */
#endif	/* _ASM_POWERPC_TIMEX_H */