Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame^] | 1 | #include <linux/init.h> |
| 2 | #include <linux/kernel.h> |
| 3 | #include <linux/string.h> |
| 4 | #include <asm/timer.h> |
| 5 | |
| 6 | #ifdef CONFIG_HPET_TIMER |
| 7 | /* |
| 8 | * HPET memory read is slower than tsc reads, but is more dependable as it |
| 9 | * always runs at constant frequency and reduces complexity due to |
| 10 | * cpufreq. So, we prefer HPET timer to tsc based one. Also, we cannot use |
| 11 | * timer_pit when HPET is active. So, we default to timer_tsc. |
| 12 | */ |
| 13 | #endif |
| 14 | /* list of timers, ordered by preference, NULL terminated */ |
| 15 | static struct init_timer_opts* __initdata timers[] = { |
| 16 | #ifdef CONFIG_X86_CYCLONE_TIMER |
| 17 | &timer_cyclone_init, |
| 18 | #endif |
| 19 | #ifdef CONFIG_HPET_TIMER |
| 20 | &timer_hpet_init, |
| 21 | #endif |
| 22 | #ifdef CONFIG_X86_PM_TIMER |
| 23 | &timer_pmtmr_init, |
| 24 | #endif |
| 25 | &timer_tsc_init, |
| 26 | &timer_pit_init, |
| 27 | NULL, |
| 28 | }; |
| 29 | |
| 30 | static char clock_override[10] __initdata; |
| 31 | |
| 32 | static int __init clock_setup(char* str) |
| 33 | { |
| 34 | if (str) |
| 35 | strlcpy(clock_override, str, sizeof(clock_override)); |
| 36 | return 1; |
| 37 | } |
| 38 | __setup("clock=", clock_setup); |
| 39 | |
| 40 | |
| 41 | /* The chosen timesource has been found to be bad. |
| 42 | * Fall back to a known good timesource (the PIT) |
| 43 | */ |
| 44 | void clock_fallback(void) |
| 45 | { |
| 46 | cur_timer = &timer_pit; |
| 47 | } |
| 48 | |
| 49 | /* iterates through the list of timers, returning the first |
| 50 | * one that initializes successfully. |
| 51 | */ |
| 52 | struct timer_opts* __init select_timer(void) |
| 53 | { |
| 54 | int i = 0; |
| 55 | |
| 56 | /* find most preferred working timer */ |
| 57 | while (timers[i]) { |
| 58 | if (timers[i]->init) |
| 59 | if (timers[i]->init(clock_override) == 0) |
| 60 | return timers[i]->opts; |
| 61 | ++i; |
| 62 | } |
| 63 | |
| 64 | panic("select_timer: Cannot find a suitable timer\n"); |
| 65 | return NULL; |
| 66 | } |