include/linux/clocksource.h

   1 /*  linux/include/linux/clocksource.h
   2  *
   3  *  This file contains the structure definitions for clocksources.
   4  *
   5  *  If you are not a clocksource, or timekeeping code, you should
   6  *  not be including this file!
   7  */
   8 #ifndef _LINUX_CLOCKSOURCE_H
   9 #define _LINUX_CLOCKSOURCE_H
  10
  11 #include <linux/types.h>
  12 #include <linux/timex.h>
  13 #include <linux/time.h>
  14 #include <linux/list.h>
  15 #include <linux/cache.h>
  16 #include <linux/timer.h>
  17 #include <asm/div64.h>
  18 #include <asm/io.h>
  19
  20 /* clocksource cycle base type */
  21 typedef u64 cycle_t;
  22 struct clocksource;
  23
  24 /**
  25  * struct cyclecounter - hardware abstraction for a free running counter
  26  *      Provides completely state-free accessors to the underlying hardware.
  27  *      Depending on which hardware it reads, the cycle counter may wrap
  28  *      around quickly. Locking rules (if necessary) have to be defined
  29  *      by the implementor and user of specific instances of this API.
  30  *
  31  * @read:               returns the current cycle value
  32  * @mask:               bitmask for two's complement
  33  *                      subtraction of non 64 bit counters,
  34  *                      see CLOCKSOURCE_MASK() helper macro
  35  * @mult:               cycle to nanosecond multiplier
  36  * @shift:              cycle to nanosecond divisor (power of two)
  37  */
  38 struct cyclecounter {
  39         cycle_t (*read)(const struct cyclecounter *cc);
  40         cycle_t mask;
  41         u32 mult;
  42         u32 shift;
  43 };
  44
  45 /**
  46  * struct timecounter - layer above a %struct cyclecounter which counts nanoseconds
  47  *      Contains the state needed by timecounter_read() to detect
  48  *      cycle counter wrap around. Initialize with
  49  *      timecounter_init(). Also used to convert cycle counts into the
  50  *      corresponding nanosecond counts with timecounter_cyc2time(). Users
  51  *      of this code are responsible for initializing the underlying
  52  *      cycle counter hardware, locking issues and reading the time
  53  *      more often than the cycle counter wraps around. The nanosecond
  54  *      counter will only wrap around after ~585 years.
  55  *
  56  * @cc:                 the cycle counter used by this instance
  57  * @cycle_last:         most recent cycle counter value seen by
  58  *                      timecounter_read()
  59  * @nsec:               continuously increasing count
  60  */
  61 struct timecounter {
  62         const struct cyclecounter *cc;
  63         cycle_t cycle_last;
  64         u64 nsec;
  65 };
  66
  67 /**
  68  * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
  69  * @tc:         Pointer to cycle counter.
  70  * @cycles:     Cycles
  71  *
  72  * XXX - This could use some mult_lxl_ll() asm optimization. Same code
  73  * as in cyc2ns, but with unsigned result.
  74  */
  75 static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
  76                                       cycle_t cycles)
  77 {
  78         u64 ret = (u64)cycles;
  79         ret = (ret * cc->mult) >> cc->shift;
  80         return ret;
  81 }
  82
  83 /**
  84  * timecounter_init - initialize a time counter
  85  * @tc:                 Pointer to time counter which is to be initialized/reset
  86  * @cc:                 A cycle counter, ready to be used.
  87  * @start_tstamp:       Arbitrary initial time stamp.
  88  *
  89  * After this call the current cycle register (roughly) corresponds to
  90  * the initial time stamp. Every call to timecounter_read() increments
  91  * the time stamp counter by the number of elapsed nanoseconds.
  92  */
  93 extern void timecounter_init(struct timecounter *tc,
  94                              const struct cyclecounter *cc,
  95                              u64 start_tstamp);
  96
  97 /**
  98  * timecounter_read - return nanoseconds elapsed since timecounter_init()
  99  *                    plus the initial time stamp
 100  * @tc:          Pointer to time counter.
 101  *
 102  * In other words, keeps track of time since the same epoch as
 103  * the function which generated the initial time stamp.
 104  */
 105 extern u64 timecounter_read(struct timecounter *tc);
 106
 107 /**
 108  * timecounter_cyc2time - convert a cycle counter to same
 109  *                        time base as values returned by
 110  *                        timecounter_read()
 111  * @tc:         Pointer to time counter.
 112  * @cycle:      a value returned by tc->cc->read()
 113  *
 114  * Cycle counts that are converted correctly as long as they
 115  * fall into the interval [-1/2 max cycle count, +1/2 max cycle count],
 116  * with "max cycle count" == cs->mask+1.
 117  *
 118  * This allows conversion of cycle counter values which were generated
 119  * in the past.
 120  */
 121 extern u64 timecounter_cyc2time(struct timecounter *tc,
 122                                 cycle_t cycle_tstamp);
 123
 124 /**
 125  * struct clocksource - hardware abstraction for a free running counter
 126  *      Provides mostly state-free accessors to the underlying hardware.
 127  *      This is the structure used for system time.
 128  *
 129  * @name:               ptr to clocksource name
 130  * @list:               list head for registration
 131  * @rating:             rating value for selection (higher is better)
 132  *                      To avoid rating inflation the following
 133  *                      list should give you a guide as to how
 134  *                      to assign your clocksource a rating
 135  *                      1-99: Unfit for real use
 136  *                              Only available for bootup and testing purposes.
 137  *                      100-199: Base level usability.
 138  *                              Functional for real use, but not desired.
 139  *                      200-299: Good.
 140  *                              A correct and usable clocksource.
 141  *                      300-399: Desired.
 142  *                              A reasonably fast and accurate clocksource.
 143  *                      400-499: Perfect
 144  *                              The ideal clocksource. A must-use where
 145  *                              available.
 146  * @read:               returns a cycle value, passes clocksource as argument
 147  * @enable:             optional function to enable the clocksource
 148  * @disable:            optional function to disable the clocksource
 149  * @mask:               bitmask for two's complement
 150  *                      subtraction of non 64 bit counters
 151  * @mult:               cycle to nanosecond multiplier (adjusted by NTP)
 152  * @mult_orig:          cycle to nanosecond multiplier (unadjusted by NTP)
 153  * @shift:              cycle to nanosecond divisor (power of two)
 154  * @flags:              flags describing special properties
 155  * @vread:              vsyscall based read
 156  * @resume:             resume function for the clocksource, if necessary
 157  * @cycle_interval:     Used internally by timekeeping core, please ignore.
 158  * @xtime_interval:     Used internally by timekeeping core, please ignore.
 159  */
 160 struct clocksource {
 161         /*
 162          * First part of structure is read mostly
 163          */
 164         char *name;
 165         struct list_head list;
 166         int rating;
 167         cycle_t (*read)(struct clocksource *cs);
 168         int (*enable)(struct clocksource *cs);
 169         void (*disable)(struct clocksource *cs);
 170         cycle_t mask;
 171         u32 mult;
 172         u32 mult_orig;
 173         u32 shift;
 174         unsigned long flags;
 175         cycle_t (*vread)(void);
 176         void (*resume)(void);
 177 #ifdef CONFIG_IA64
 178         void *fsys_mmio;        /* used by fsyscall asm code */
 179 #define CLKSRC_FSYS_MMIO_SET(mmio, addr)      ((mmio) = (addr))
 180 #else
 181 #define CLKSRC_FSYS_MMIO_SET(mmio, addr)      do { } while (0)
 182 #endif
 183
 184         /* timekeeping specific data, ignore */
 185         cycle_t cycle_interval;
 186         u64     xtime_interval;
 187         u32     raw_interval;
 188         /*
 189          * Second part is written at each timer interrupt
 190          * Keep it in a different cache line to dirty no
 191          * more than one cache line.
 192          */
 193         cycle_t cycle_last ____cacheline_aligned_in_smp;
 194         u64 xtime_nsec;
 195         s64 error;
 196         struct timespec raw_time;
 197
 198 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
 199         /* Watchdog related data, used by the framework */
 200         struct list_head wd_list;
 201         cycle_t wd_last;
 202 #endif
 203 };
 204
 205 extern struct clocksource *clock;       /* current clocksource */
 206
 207 /*
 208  * Clock source flags bits::
 209  */
 210 #define CLOCK_SOURCE_IS_CONTINUOUS              0x01
 211 #define CLOCK_SOURCE_MUST_VERIFY                0x02
 212
 213 #define CLOCK_SOURCE_WATCHDOG                   0x10
 214 #define CLOCK_SOURCE_VALID_FOR_HRES             0x20
 215
 216 /* simplify initialization of mask field */
 217 #define CLOCKSOURCE_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
 218
 219 /**
 220  * clocksource_khz2mult - calculates mult from khz and shift
 221  * @khz:                Clocksource frequency in KHz
 222  * @shift_constant:     Clocksource shift factor
 223  *
 224  * Helper functions that converts a khz counter frequency to a timsource
 225  * multiplier, given the clocksource shift value
 226  */
 227 static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
 228 {
 229         /*  khz = cyc/(Million ns)
 230          *  mult/2^shift  = ns/cyc
 231          *  mult = ns/cyc * 2^shift
 232          *  mult = 1Million/khz * 2^shift
 233          *  mult = 1000000 * 2^shift / khz
 234          *  mult = (1000000<<shift) / khz
 235          */
 236         u64 tmp = ((u64)1000000) << shift_constant;
 237
 238         tmp += khz/2; /* round for do_div */
 239         do_div(tmp, khz);
 240
 241         return (u32)tmp;
 242 }
 243
 244 /**
 245  * clocksource_hz2mult - calculates mult from hz and shift
 246  * @hz:                 Clocksource frequency in Hz
 247  * @shift_constant:     Clocksource shift factor
 248  *
 249  * Helper functions that converts a hz counter
 250  * frequency to a timsource multiplier, given the
 251  * clocksource shift value
 252  */
 253 static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
 254 {
 255         /*  hz = cyc/(Billion ns)
 256          *  mult/2^shift  = ns/cyc
 257          *  mult = ns/cyc * 2^shift
 258          *  mult = 1Billion/hz * 2^shift
 259          *  mult = 1000000000 * 2^shift / hz
 260          *  mult = (1000000000<<shift) / hz
 261          */
 262         u64 tmp = ((u64)1000000000) << shift_constant;
 263
 264         tmp += hz/2; /* round for do_div */
 265         do_div(tmp, hz);
 266
 267         return (u32)tmp;
 268 }
 269
 270 /**
 271  * clocksource_read: - Access the clocksource's current cycle value
 272  * @cs:         pointer to clocksource being read
 273  *
 274  * Uses the clocksource to return the current cycle_t value
 275  */
 276 static inline cycle_t clocksource_read(struct clocksource *cs)
 277 {
 278         return cs->read(cs);
 279 }
 280
 281 /**
 282  * clocksource_enable: - enable clocksource
 283  * @cs:         pointer to clocksource
 284  *
 285  * Enables the specified clocksource. The clocksource callback
 286  * function should start up the hardware and setup mult and field
 287  * members of struct clocksource to reflect hardware capabilities.
 288  */
 289 static inline int clocksource_enable(struct clocksource *cs)
 290 {
 291         int ret = 0;
 292
 293         if (cs->enable)
 294                 ret = cs->enable(cs);
 295
 296         /*
 297          * The frequency may have changed while the clocksource
 298          * was disabled. If so the code in ->enable() must update
 299          * the mult value to reflect the new frequency. Make sure
 300          * mult_orig follows this change.
 301          */
 302         cs->mult_orig = cs->mult;
 303
 304         return ret;
 305 }
 306
 307 /**
 308  * clocksource_disable: - disable clocksource
 309  * @cs:         pointer to clocksource
 310  *
 311  * Disables the specified clocksource. The clocksource callback
 312  * function should power down the now unused hardware block to
 313  * save power.
 314  */
 315 static inline void clocksource_disable(struct clocksource *cs)
 316 {
 317         /*
 318          * Save mult_orig in mult so clocksource_enable() can
 319          * restore the value regardless if ->enable() updates
 320          * the value of mult or not.
 321          */
 322         cs->mult = cs->mult_orig;
 323
 324         if (cs->disable)
 325                 cs->disable(cs);
 326 }
 327
 328 /**
 329  * cyc2ns - converts clocksource cycles to nanoseconds
 330  * @cs:         Pointer to clocksource
 331  * @cycles:     Cycles
 332  *
 333  * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
 334  *
 335  * XXX - This could use some mult_lxl_ll() asm optimization
 336  */
 337 static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
 338 {
 339         u64 ret = (u64)cycles;
 340         ret = (ret * cs->mult) >> cs->shift;
 341         return ret;
 342 }
 343
 344 /**
 345  * clocksource_calculate_interval - Calculates a clocksource interval struct
 346  *
 347  * @c:          Pointer to clocksource.
 348  * @length_nsec: Desired interval length in nanoseconds.
 349  *
 350  * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
 351  * pair and interval request.
 352  *
 353  * Unless you're the timekeeping code, you should not be using this!
 354  */
 355 static inline void clocksource_calculate_interval(struct clocksource *c,
 356                                                   unsigned long length_nsec)
 357 {
 358         u64 tmp;
 359
 360         /* Do the ns -> cycle conversion first, using original mult */
 361         tmp = length_nsec;
 362         tmp <<= c->shift;
 363         tmp += c->mult_orig/2;
 364         do_div(tmp, c->mult_orig);
 365
 366         c->cycle_interval = (cycle_t)tmp;
 367         if (c->cycle_interval == 0)
 368                 c->cycle_interval = 1;
 369
 370         /* Go back from cycles -> shifted ns, this time use ntp adjused mult */
 371         c->xtime_interval = (u64)c->cycle_interval * c->mult;
 372         c->raw_interval = ((u64)c->cycle_interval * c->mult_orig) >> c->shift;
 373 }
 374
 375
 376 /* used to install a new clocksource */
 377 extern int clocksource_register(struct clocksource*);
 378 extern void clocksource_unregister(struct clocksource*);
 379 extern void clocksource_touch_watchdog(void);
 380 extern struct clocksource* clocksource_get_next(void);
 381 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 382 extern void clocksource_resume(void);
 383
 384 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
 385 extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
 386 extern void update_vsyscall_tz(void);
 387 #else
 388 static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
 389 {
 390 }
 391
 392 static inline void update_vsyscall_tz(void)
 393 {
 394 }
 395 #endif
 396
 397 #endif /* _LINUX_CLOCKSOURCE_H */