arch/i386/kernel/tsc.c

   1 /*
   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.
   5  */
   6
   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>
  13
  14 #include <asm/delay.h>
  15 #include <asm/tsc.h>
  16 #include <asm/io.h>
  17 #include <asm/timer.h>
  18
  19 #include "mach_timer.h"
  20
  21 /*
  22  * On some systems the TSC frequency does not
  23  * change with the cpu frequency. So we need
  24  * an extra value to store the TSC freq
  25  */
  26 unsigned int tsc_khz;
  27 unsigned long long (*custom_sched_clock)(void);
  28
  29 int tsc_disable;
  30
  31 #ifdef CONFIG_X86_TSC
  32 static int __init tsc_setup(char *str)
  33 {
  34         printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
  35                                 "cannot disable TSC.\n");
  36         return 1;
  37 }
  38 #else
  39 /*
  40  * disable flag for tsc. Takes effect by clearing the TSC cpu flag
  41  * in cpu/common.c
  42  */
  43 static int __init tsc_setup(char *str)
  44 {
  45         tsc_disable = 1;
  46
  47         return 1;
  48 }
  49 #endif
  50
  51 __setup("notsc", tsc_setup);
  52
  53 /*
  54  * code to mark and check if the TSC is unstable
  55  * due to cpufreq or due to unsynced TSCs
  56  */
  57 static int tsc_unstable;
  58
  59 static inline int check_tsc_unstable(void)
  60 {
  61         return tsc_unstable;
  62 }
  63
  64 /* Accellerators for sched_clock()
  65  * convert from cycles(64bits) => nanoseconds (64bits)
  66  *  basic equation:
  67  *              ns = cycles / (freq / ns_per_sec)
  68  *              ns = cycles * (ns_per_sec / freq)
  69  *              ns = cycles * (10^9 / (cpu_khz * 10^3))
  70  *              ns = cycles * (10^6 / cpu_khz)
  71  *
  72  *      Then we use scaling math (suggested by george@mvista.com) to get:
  73  *              ns = cycles * (10^6 * SC / cpu_khz) / SC
  74  *              ns = cycles * cyc2ns_scale / SC
  75  *
  76  *      And since SC is a constant power of two, we can convert the div
  77  *  into a shift.
  78  *
  79  *  We can use khz divisor instead of mhz to keep a better percision, since
  80  *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
  81  *  (mathieu.desnoyers@polymtl.ca)
  82  *
  83  *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
  84  */
  85 static unsigned long cyc2ns_scale __read_mostly;
  86
  87 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
  88
  89 static inline void set_cyc2ns_scale(unsigned long cpu_khz)
  90 {
  91         cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;
  92 }
  93
  94 static inline unsigned long long cycles_2_ns(unsigned long long cyc)
  95 {
  96         return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
  97 }
  98
  99 /*
 100  * Scheduler clock - returns current time in nanosec units.
 101  */
 102 unsigned long long sched_clock(void)
 103 {
 104         unsigned long long this_offset;
 105
 106         /*
 107          * Fall back to jiffies if there's no TSC available:
 108          */
 109         if (unlikely(tsc_disable))
 110                 /* No locking but a rare wrong value is not a big deal: */
 111                 return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
 112
 113         /* read the Time Stamp Counter: */
 114         get_scheduled_cycles(this_offset);
 115
 116         /* return the value in ns */
 117         return cycles_2_ns(this_offset);
 118 }
 119
 120 unsigned long native_calculate_cpu_khz(void)
 121 {
 122         unsigned long long start, end;
 123         unsigned long count;
 124         u64 delta64;
 125         int i;
 126         unsigned long flags;
 127
 128         local_irq_save(flags);
 129
 130         /* run 3 times to ensure the cache is warm */
 131         for (i = 0; i < 3; i++) {
 132                 mach_prepare_counter();
 133                 rdtscll(start);
 134                 mach_countup(&count);
 135                 rdtscll(end);
 136         }
 137         /*
 138          * Error: ECTCNEVERSET
 139          * The CTC wasn't reliable: we got a hit on the very first read,
 140          * or the CPU was so fast/slow that the quotient wouldn't fit in
 141          * 32 bits..
 142          */
 143         if (count <= 1)
 144                 goto err;
 145
 146         delta64 = end - start;
 147
 148         /* cpu freq too fast: */
 149         if (delta64 > (1ULL<<32))
 150                 goto err;
 151
 152         /* cpu freq too slow: */
 153         if (delta64 <= CALIBRATE_TIME_MSEC)
 154                 goto err;
 155
 156         delta64 += CALIBRATE_TIME_MSEC/2; /* round for do_div */
 157         do_div(delta64,CALIBRATE_TIME_MSEC);
 158
 159         local_irq_restore(flags);
 160         return (unsigned long)delta64;
 161 err:
 162         local_irq_restore(flags);
 163         return 0;
 164 }
 165
 166 int recalibrate_cpu_khz(void)
 167 {
 168 #ifndef CONFIG_SMP
 169         unsigned long cpu_khz_old = cpu_khz;
 170
 171         if (cpu_has_tsc) {
 172                 cpu_khz = calculate_cpu_khz();
 173                 tsc_khz = cpu_khz;
 174                 cpu_data[0].loops_per_jiffy =
 175                         cpufreq_scale(cpu_data[0].loops_per_jiffy,
 176                                         cpu_khz_old, cpu_khz);
 177                 return 0;
 178         } else
 179                 return -ENODEV;
 180 #else
 181         return -ENODEV;
 182 #endif
 183 }
 184
 185 EXPORT_SYMBOL(recalibrate_cpu_khz);
 186
 187 #ifdef CONFIG_CPU_FREQ
 188
 189 /*
 190  * if the CPU frequency is scaled, TSC-based delays will need a different
 191  * loops_per_jiffy value to function properly.
 192  */
 193 static unsigned int ref_freq = 0;
 194 static unsigned long loops_per_jiffy_ref = 0;
 195 static unsigned long cpu_khz_ref = 0;
 196
 197 static int
 198 time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
 199 {
 200         struct cpufreq_freqs *freq = data;
 201
 202         if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE)
 203                 write_seqlock_irq(&xtime_lock);
 204
 205         if (!ref_freq) {
 206                 if (!freq->old){
 207                         ref_freq = freq->new;
 208                         goto end;
 209                 }
 210                 ref_freq = freq->old;
 211                 loops_per_jiffy_ref = cpu_data[freq->cpu].loops_per_jiffy;
 212                 cpu_khz_ref = cpu_khz;
 213         }
 214
 215         if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
 216             (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
 217             (val == CPUFREQ_RESUMECHANGE)) {
 218                 if (!(freq->flags & CPUFREQ_CONST_LOOPS))
 219                         cpu_data[freq->cpu].loops_per_jiffy =
 220                                 cpufreq_scale(loops_per_jiffy_ref,
 221                                                 ref_freq, freq->new);
 222
 223                 if (cpu_khz) {
 224
 225                         if (num_online_cpus() == 1)
 226                                 cpu_khz = cpufreq_scale(cpu_khz_ref,
 227                                                 ref_freq, freq->new);
 228                         if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
 229                                 tsc_khz = cpu_khz;
 230                                 set_cyc2ns_scale(cpu_khz);
 231                                 /*
 232                                  * TSC based sched_clock turns
 233                                  * to junk w/ cpufreq
 234                                  */
 235                                 mark_tsc_unstable();
 236                         }
 237                 }
 238         }
 239 end:
 240         if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE)
 241                 write_sequnlock_irq(&xtime_lock);
 242
 243         return 0;
 244 }
 245
 246 static struct notifier_block time_cpufreq_notifier_block = {
 247         .notifier_call  = time_cpufreq_notifier
 248 };
 249
 250 static int __init cpufreq_tsc(void)
 251 {
 252         return cpufreq_register_notifier(&time_cpufreq_notifier_block,
 253                                          CPUFREQ_TRANSITION_NOTIFIER);
 254 }
 255 core_initcall(cpufreq_tsc);
 256
 257 #endif
 258
 259 /* clock source code */
 260
 261 static unsigned long current_tsc_khz = 0;
 262
 263 static cycle_t read_tsc(void)
 264 {
 265         cycle_t ret;
 266
 267         rdtscll(ret);
 268
 269         return ret;
 270 }
 271
 272 static struct clocksource clocksource_tsc = {
 273         .name                   = "tsc",
 274         .rating                 = 300,
 275         .read                   = read_tsc,
 276         .mask                   = CLOCKSOURCE_MASK(64),
 277         .mult                   = 0, /* to be set */
 278         .shift                  = 22,
 279         .flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
 280                                   CLOCK_SOURCE_MUST_VERIFY,
 281 };
 282
 283 void mark_tsc_unstable(void)
 284 {
 285         if (!tsc_unstable) {
 286                 tsc_unstable = 1;
 287                 /* Can be called before registration */
 288                 if (clocksource_tsc.mult)
 289                         clocksource_change_rating(&clocksource_tsc, 0);
 290                 else
 291                         clocksource_tsc.rating = 0;
 292         }
 293 }
 294 EXPORT_SYMBOL_GPL(mark_tsc_unstable);
 295
 296 static int __init dmi_mark_tsc_unstable(struct dmi_system_id *d)
 297 {
 298         printk(KERN_NOTICE "%s detected: marking TSC unstable.\n",
 299                        d->ident);
 300         tsc_unstable = 1;
 301         return 0;
 302 }
 303
 304 /* List of systems that have known TSC problems */
 305 static struct dmi_system_id __initdata bad_tsc_dmi_table[] = {
 306         {
 307          .callback = dmi_mark_tsc_unstable,
 308          .ident = "IBM Thinkpad 380XD",
 309          .matches = {
 310                      DMI_MATCH(DMI_BOARD_VENDOR, "IBM"),
 311                      DMI_MATCH(DMI_BOARD_NAME, "2635FA0"),
 312                      },
 313          },
 314          {}
 315 };
 316
 317 /*
 318  * Make an educated guess if the TSC is trustworthy and synchronized
 319  * over all CPUs.
 320  */
 321 __cpuinit int unsynchronized_tsc(void)
 322 {
 323         if (!cpu_has_tsc || tsc_unstable)
 324                 return 1;
 325         /*
 326          * Intel systems are normally all synchronized.
 327          * Exceptions must mark TSC as unstable:
 328          */
 329         if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
 330                 /* assume multi socket systems are not synchronized: */
 331                 if (num_possible_cpus() > 1)
 332                         tsc_unstable = 1;
 333         }
 334         return tsc_unstable;
 335 }
 336
 337 /*
 338  * Geode_LX - the OLPC CPU has a possibly a very reliable TSC
 339  */
 340 #ifdef CONFIG_MGEODE_LX
 341 /* RTSC counts during suspend */
 342 #define RTSC_SUSP 0x100
 343
 344 static void __init check_geode_tsc_reliable(void)
 345 {
 346         unsigned long val;
 347
 348         rdmsrl(MSR_GEODE_BUSCONT_CONF0, val);
 349         if ((val & RTSC_SUSP))
 350                 clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
 351 }
 352 #else
 353 static inline void check_geode_tsc_reliable(void) { }
 354 #endif
 355
 356
 357 void __init tsc_init(void)
 358 {
 359         if (!cpu_has_tsc || tsc_disable)
 360                 goto out_no_tsc;
 361
 362         cpu_khz = calculate_cpu_khz();
 363         tsc_khz = cpu_khz;
 364
 365         if (!cpu_khz)
 366                 goto out_no_tsc;
 367
 368         printk("Detected %lu.%03lu MHz processor.\n",
 369                                 (unsigned long)cpu_khz / 1000,
 370                                 (unsigned long)cpu_khz % 1000);
 371
 372         set_cyc2ns_scale(cpu_khz);
 373         use_tsc_delay();
 374
 375         /* Check and install the TSC clocksource */
 376         dmi_check_system(bad_tsc_dmi_table);
 377
 378         unsynchronized_tsc();
 379         check_geode_tsc_reliable();
 380         current_tsc_khz = tsc_khz;
 381         clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
 382                                                         clocksource_tsc.shift);
 383         /* lower the rating if we already know its unstable: */
 384         if (check_tsc_unstable()) {
 385                 clocksource_tsc.rating = 0;
 386                 clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
 387         }
 388         clocksource_register(&clocksource_tsc);
 389
 390         return;
 391
 392 out_no_tsc:
 393         /*
 394          * Set the tsc_disable flag if there's no TSC support, this
 395          * makes it a fast flag for the kernel to see whether it
 396          * should be using the TSC.
 397          */
 398         tsc_disable = 1;
 399 }