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