?? timer.c
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#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;}
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