#include <linux/init.h>#include <linux/kernel.h>#include <linux/string.h>#include <asm/timer.h>#ifdef CONFIG_HPET_TIMER/* * HPET memory read is slower than tsc reads, but is more dependable as it * always runs at constant frequency and reduces complexity due to * cpufreq. So, we prefer HPET timer to tsc based one. Also, we cannot use * timer_pit when HPET is active. So, we default to timer_tsc. */#endif/* list of timers, ordered by preference, NULL terminated */static struct timer_opts* timers[] = {#ifdef CONFIG_X86_CYCLONE_TIMER	&timer_cyclone,#endif#ifdef CONFIG_HPET_TIMER	&timer_hpet,#endif#ifdef CONFIG_X86_PM_TIMER	&timer_pmtmr,#endif	&timer_tsc,	&timer_pit,	NULL,};static char clock_override[10] __initdata;static int __init clock_setup(char* str){	if (str)		strlcpy(clock_override, str, sizeof(clock_override));	return 1;}__setup("clock=", clock_setup);/* The chosen timesource has been found to be bad. * Fall back to a known good timesource (the PIT) */void clock_fallback(void){	cur_timer = &timer_pit;}/* iterates through the list of timers, returning the first  * one that initializes successfully. */struct timer_opts* select_timer(void){	int i = 0;		/* find most preferred working timer */	while (timers[i]) {		if (timers[i]->init)			if (timers[i]->init(clock_override) == 0)				return timers[i];		++i;	}			panic("select_timer: Cannot find a suitable timer\n");	return NULL;}