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