2 * This code largely moved from arch/i386/kernel/timer/timer_tsc.c
3 * which was originally moved from arch/i386/kernel/time.c.
4 * See comments there for proper credits.
7 #include <linux/clocksource.h>
8 #include <linux/workqueue.h>
9 #include <linux/cpufreq.h>
10 #include <linux/jiffies.h>
11 #include <linux/init.h>
12 #include <linux/dmi.h>
14 #include <asm/delay.h>
17 #include <asm/timer.h>
19 #include "mach_timer.h"
21 static int tsc_enabled;
24 * On some systems the TSC frequency does not
25 * change with the cpu frequency. So we need
26 * an extra value to store the TSC freq
33 static int __init tsc_setup(char *str)
35 printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
36 "cannot disable TSC.\n");
41 * disable flag for tsc. Takes effect by clearing the TSC cpu flag
44 static int __init tsc_setup(char *str)
52 __setup("notsc", tsc_setup);
55 * code to mark and check if the TSC is unstable
56 * due to cpufreq or due to unsynced TSCs
58 static int tsc_unstable;
60 static inline int check_tsc_unstable(void)
65 /* Accellerators for sched_clock()
66 * convert from cycles(64bits) => nanoseconds (64bits)
68 * ns = cycles / (freq / ns_per_sec)
69 * ns = cycles * (ns_per_sec / freq)
70 * ns = cycles * (10^9 / (cpu_khz * 10^3))
71 * ns = cycles * (10^6 / cpu_khz)
73 * Then we use scaling math (suggested by george@mvista.com) to get:
74 * ns = cycles * (10^6 * SC / cpu_khz) / SC
75 * ns = cycles * cyc2ns_scale / SC
77 * And since SC is a constant power of two, we can convert the div
80 * We can use khz divisor instead of mhz to keep a better percision, since
81 * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
82 * (mathieu.desnoyers@polymtl.ca)
84 * -johnstul@us.ibm.com "math is hard, lets go shopping!"
86 static unsigned long cyc2ns_scale __read_mostly;
88 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
90 static inline void set_cyc2ns_scale(unsigned long cpu_khz)
92 cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;
95 static inline unsigned long long cycles_2_ns(unsigned long long cyc)
97 return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
101 * Scheduler clock - returns current time in nanosec units.
103 unsigned long long sched_clock(void)
105 unsigned long long this_offset;
108 * Fall back to jiffies if there's no TSC available:
110 if (unlikely(!tsc_enabled))
111 /* No locking but a rare wrong value is not a big deal: */
112 return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
114 /* read the Time Stamp Counter: */
115 get_scheduled_cycles(this_offset);
117 /* return the value in ns */
118 return cycles_2_ns(this_offset);
121 unsigned long native_calculate_cpu_khz(void)
123 unsigned long long start, end;
129 local_irq_save(flags);
131 /* run 3 times to ensure the cache is warm */
132 for (i = 0; i < 3; i++) {
133 mach_prepare_counter();
135 mach_countup(&count);
139 * Error: ECTCNEVERSET
140 * The CTC wasn't reliable: we got a hit on the very first read,
141 * or the CPU was so fast/slow that the quotient wouldn't fit in
147 delta64 = end - start;
149 /* cpu freq too fast: */
150 if (delta64 > (1ULL<<32))
153 /* cpu freq too slow: */
154 if (delta64 <= CALIBRATE_TIME_MSEC)
157 delta64 += CALIBRATE_TIME_MSEC/2; /* round for do_div */
158 do_div(delta64,CALIBRATE_TIME_MSEC);
160 local_irq_restore(flags);
161 return (unsigned long)delta64;
163 local_irq_restore(flags);
167 int recalibrate_cpu_khz(void)
170 unsigned long cpu_khz_old = cpu_khz;
173 cpu_khz = calculate_cpu_khz();
175 cpu_data[0].loops_per_jiffy =
176 cpufreq_scale(cpu_data[0].loops_per_jiffy,
177 cpu_khz_old, cpu_khz);
186 EXPORT_SYMBOL(recalibrate_cpu_khz);
188 #ifdef CONFIG_CPU_FREQ
191 * if the CPU frequency is scaled, TSC-based delays will need a different
192 * loops_per_jiffy value to function properly.
194 static unsigned int ref_freq = 0;
195 static unsigned long loops_per_jiffy_ref = 0;
196 static unsigned long cpu_khz_ref = 0;
199 time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
201 struct cpufreq_freqs *freq = data;
203 if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE)
204 write_seqlock_irq(&xtime_lock);
208 ref_freq = freq->new;
211 ref_freq = freq->old;
212 loops_per_jiffy_ref = cpu_data[freq->cpu].loops_per_jiffy;
213 cpu_khz_ref = cpu_khz;
216 if ((val == CPUFREQ_PRECHANGE && freq->old < freq->new) ||
217 (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
218 (val == CPUFREQ_RESUMECHANGE)) {
219 if (!(freq->flags & CPUFREQ_CONST_LOOPS))
220 cpu_data[freq->cpu].loops_per_jiffy =
221 cpufreq_scale(loops_per_jiffy_ref,
222 ref_freq, freq->new);
226 if (num_online_cpus() == 1)
227 cpu_khz = cpufreq_scale(cpu_khz_ref,
228 ref_freq, freq->new);
229 if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
231 set_cyc2ns_scale(cpu_khz);
233 * TSC based sched_clock turns
236 mark_tsc_unstable("cpufreq changes");
241 if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE)
242 write_sequnlock_irq(&xtime_lock);
247 static struct notifier_block time_cpufreq_notifier_block = {
248 .notifier_call = time_cpufreq_notifier
251 static int __init cpufreq_tsc(void)
253 return cpufreq_register_notifier(&time_cpufreq_notifier_block,
254 CPUFREQ_TRANSITION_NOTIFIER);
256 core_initcall(cpufreq_tsc);
260 /* clock source code */
262 static unsigned long current_tsc_khz = 0;
264 static cycle_t read_tsc(void)
273 static struct clocksource clocksource_tsc = {
277 .mask = CLOCKSOURCE_MASK(64),
278 .mult = 0, /* to be set */
280 .flags = CLOCK_SOURCE_IS_CONTINUOUS |
281 CLOCK_SOURCE_MUST_VERIFY,
284 void mark_tsc_unstable(char *reason)
289 printk("Marking TSC unstable due to: %s.\n", reason);
290 /* Can be called before registration */
291 if (clocksource_tsc.mult)
292 clocksource_change_rating(&clocksource_tsc, 0);
294 clocksource_tsc.rating = 0;
297 EXPORT_SYMBOL_GPL(mark_tsc_unstable);
299 static int __init dmi_mark_tsc_unstable(struct dmi_system_id *d)
301 printk(KERN_NOTICE "%s detected: marking TSC unstable.\n",
307 /* List of systems that have known TSC problems */
308 static struct dmi_system_id __initdata bad_tsc_dmi_table[] = {
310 .callback = dmi_mark_tsc_unstable,
311 .ident = "IBM Thinkpad 380XD",
313 DMI_MATCH(DMI_BOARD_VENDOR, "IBM"),
314 DMI_MATCH(DMI_BOARD_NAME, "2635FA0"),
321 * Make an educated guess if the TSC is trustworthy and synchronized
324 __cpuinit int unsynchronized_tsc(void)
326 if (!cpu_has_tsc || tsc_unstable)
329 * Intel systems are normally all synchronized.
330 * Exceptions must mark TSC as unstable:
332 if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
333 /* assume multi socket systems are not synchronized: */
334 if (num_possible_cpus() > 1)
341 * Geode_LX - the OLPC CPU has a possibly a very reliable TSC
343 #ifdef CONFIG_MGEODE_LX
344 /* RTSC counts during suspend */
345 #define RTSC_SUSP 0x100
347 static void __init check_geode_tsc_reliable(void)
351 rdmsrl(MSR_GEODE_BUSCONT_CONF0, val);
352 if ((val & RTSC_SUSP))
353 clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
356 static inline void check_geode_tsc_reliable(void) { }
360 void __init tsc_init(void)
362 if (!cpu_has_tsc || tsc_disable)
365 cpu_khz = calculate_cpu_khz();
371 printk("Detected %lu.%03lu MHz processor.\n",
372 (unsigned long)cpu_khz / 1000,
373 (unsigned long)cpu_khz % 1000);
375 set_cyc2ns_scale(cpu_khz);
378 /* Check and install the TSC clocksource */
379 dmi_check_system(bad_tsc_dmi_table);
381 unsynchronized_tsc();
382 check_geode_tsc_reliable();
383 current_tsc_khz = tsc_khz;
384 clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
385 clocksource_tsc.shift);
386 /* lower the rating if we already know its unstable: */
387 if (check_tsc_unstable()) {
388 clocksource_tsc.rating = 0;
389 clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
393 clocksource_register(&clocksource_tsc);
399 * Set the tsc_disable flag if there's no TSC support, this
400 * makes it a fast flag for the kernel to see whether it
401 * should be using the TSC.