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 <linux/init.h>
  18 #include <asm/div64.h>
  19 #include <asm/io.h>
  20
  21 /* clocksource cycle base type */
  22 typedef u64 cycle_t;
  23 struct clocksource;
  24
  25 /**
  26  * struct cyclecounter - hardware abstraction for a free running counter
  27  *      Provides completely state-free accessors to the underlying hardware.
  28  *      Depending on which hardware it reads, the cycle counter may wrap
  29  *      around quickly. Locking rules (if necessary) have to be defined
  30  *      by the implementor and user of specific instances of this API.
  31  *
  32  * @read:               returns the current cycle value
  33  * @mask:               bitmask for two's complement
  34  *                      subtraction of non 64 bit counters,
  35  *                      see CLOCKSOURCE_MASK() helper macro
  36  * @mult:               cycle to nanosecond multiplier
  37  * @shift:              cycle to nanosecond divisor (power of two)
  38  */
  39 struct cyclecounter {
  40         cycle_t (*read)(const struct cyclecounter *cc);
  41         cycle_t mask;
  42         u32 mult;
  43         u32 shift;
  44 };
  45
  46 /**
  47  * struct timecounter - layer above a %struct cyclecounter which counts nanoseconds
  48  *      Contains the state needed by timecounter_read() to detect
  49  *      cycle counter wrap around. Initialize with
  50  *      timecounter_init(). Also used to convert cycle counts into the
  51  *      corresponding nanosecond counts with timecounter_cyc2time(). Users
  52  *      of this code are responsible for initializing the underlying
  53  *      cycle counter hardware, locking issues and reading the time
  54  *      more often than the cycle counter wraps around. The nanosecond
  55  *      counter will only wrap around after ~585 years.
  56  *
  57  * @cc:                 the cycle counter used by this instance
  58  * @cycle_last:         most recent cycle counter value seen by
  59  *                      timecounter_read()
  60  * @nsec:               continuously increasing count
  61  */
  62 struct timecounter {
  63         const struct cyclecounter *cc;
  64         cycle_t cycle_last;
  65         u64 nsec;
  66 };
  67
  68 /**
  69  * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
  70  * @tc:         Pointer to cycle counter.
  71  * @cycles:     Cycles
  72  *
  73  * XXX - This could use some mult_lxl_ll() asm optimization. Same code
  74  * as in cyc2ns, but with unsigned result.
  75  */
  76 static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
  77                                       cycle_t cycles)
  78 {
  79         u64 ret = (u64)cycles;
  80         ret = (ret * cc->mult) >> cc->shift;
  81         return ret;
  82 }
  83
  84 /**
  85  * timecounter_init - initialize a time counter
  86  * @tc:                 Pointer to time counter which is to be initialized/reset
  87  * @cc:                 A cycle counter, ready to be used.
  88  * @start_tstamp:       Arbitrary initial time stamp.
  89  *
  90  * After this call the current cycle register (roughly) corresponds to
  91  * the initial time stamp. Every call to timecounter_read() increments
  92  * the time stamp counter by the number of elapsed nanoseconds.
  93  */
  94 extern void timecounter_init(struct timecounter *tc,
  95                              const struct cyclecounter *cc,
  96                              u64 start_tstamp);
  97
  98 /**
  99  * timecounter_read - return nanoseconds elapsed since timecounter_init()
 100  *                    plus the initial time stamp
 101  * @tc:          Pointer to time counter.
 102  *
 103  * In other words, keeps track of time since the same epoch as
 104  * the function which generated the initial time stamp.
 105  */
 106 extern u64 timecounter_read(struct timecounter *tc);
 107
 108 /**
 109  * timecounter_cyc2time - convert a cycle counter to same
 110  *                        time base as values returned by
 111  *                        timecounter_read()
 112  * @tc:         Pointer to time counter.
 113  * @cycle:      a value returned by tc->cc->read()
 114  *
 115  * Cycle counts that are converted correctly as long as they
 116  * fall into the interval [-1/2 max cycle count, +1/2 max cycle count],
 117  * with "max cycle count" == cs->mask+1.
 118  *
 119  * This allows conversion of cycle counter values which were generated
 120  * in the past.
 121  */
 122 extern u64 timecounter_cyc2time(struct timecounter *tc,
 123                                 cycle_t cycle_tstamp);
 124
 125 /**
 126  * struct clocksource - hardware abstraction for a free running counter
 127  *      Provides mostly state-free accessors to the underlying hardware.
 128  *      This is the structure used for system time.
 129  *
 130  * @name:               ptr to clocksource name
 131  * @list:               list head for registration
 132  * @rating:             rating value for selection (higher is better)
 133  *                      To avoid rating inflation the following
 134  *                      list should give you a guide as to how
 135  *                      to assign your clocksource a rating
 136  *                      1-99: Unfit for real use
 137  *                              Only available for bootup and testing purposes.
 138  *                      100-199: Base level usability.
 139  *                              Functional for real use, but not desired.
 140  *                      200-299: Good.
 141  *                              A correct and usable clocksource.
 142  *                      300-399: Desired.
 143  *                              A reasonably fast and accurate clocksource.
 144  *                      400-499: Perfect
 145  *                              The ideal clocksource. A must-use where
 146  *                              available.
 147  * @read:               returns a cycle value, passes clocksource as argument
 148  * @enable:             optional function to enable the clocksource
 149  * @disable:            optional function to disable the clocksource
 150  * @mask:               bitmask for two's complement
 151  *                      subtraction of non 64 bit counters
 152  * @mult:               cycle to nanosecond multiplier
 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  */
 158 struct clocksource {
 159         /*
 160          * First part of structure is read mostly
 161          */
 162         char *name;
 163         struct list_head list;
 164         int rating;
 165         cycle_t (*read)(struct clocksource *cs);
 166         int (*enable)(struct clocksource *cs);
 167         void (*disable)(struct clocksource *cs);
 168         cycle_t mask;
 169         u32 mult;
 170         u32 shift;
 171         unsigned long flags;
 172         cycle_t (*vread)(void);
 173         void (*resume)(void);
 174 #ifdef CONFIG_IA64
 175         void *fsys_mmio;        /* used by fsyscall asm code */
 176 #define CLKSRC_FSYS_MMIO_SET(mmio, addr)      ((mmio) = (addr))
 177 #else
 178 #define CLKSRC_FSYS_MMIO_SET(mmio, addr)      do { } while (0)
 179 #endif
 180
 181         /*
 182          * Second part is written at each timer interrupt
 183          * Keep it in a different cache line to dirty no
 184          * more than one cache line.
 185          */
 186         cycle_t cycle_last ____cacheline_aligned_in_smp;
 187
 188 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
 189         /* Watchdog related data, used by the framework */
 190         struct list_head wd_list;
 191         cycle_t wd_last;
 192 #endif
 193 };
 194
 195 /*
 196  * Clock source flags bits::
 197  */
 198 #define CLOCK_SOURCE_IS_CONTINUOUS              0x01
 199 #define CLOCK_SOURCE_MUST_VERIFY                0x02
 200
 201 #define CLOCK_SOURCE_WATCHDOG                   0x10
 202 #define CLOCK_SOURCE_VALID_FOR_HRES             0x20
 203 #define CLOCK_SOURCE_UNSTABLE                   0x40
 204
 205 /* simplify initialization of mask field */
 206 #define CLOCKSOURCE_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
 207
 208 /**
 209  * clocksource_khz2mult - calculates mult from khz and shift
 210  * @khz:                Clocksource frequency in KHz
 211  * @shift_constant:     Clocksource shift factor
 212  *
 213  * Helper functions that converts a khz counter frequency to a timsource
 214  * multiplier, given the clocksource shift value
 215  */
 216 static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
 217 {
 218         /*  khz = cyc/(Million ns)
 219          *  mult/2^shift  = ns/cyc
 220          *  mult = ns/cyc * 2^shift
 221          *  mult = 1Million/khz * 2^shift
 222          *  mult = 1000000 * 2^shift / khz
 223          *  mult = (1000000<<shift) / khz
 224          */
 225         u64 tmp = ((u64)1000000) << shift_constant;
 226
 227         tmp += khz/2; /* round for do_div */
 228         do_div(tmp, khz);
 229
 230         return (u32)tmp;
 231 }
 232
 233 /**
 234  * clocksource_hz2mult - calculates mult from hz and shift
 235  * @hz:                 Clocksource frequency in Hz
 236  * @shift_constant:     Clocksource shift factor
 237  *
 238  * Helper functions that converts a hz counter
 239  * frequency to a timsource multiplier, given the
 240  * clocksource shift value
 241  */
 242 static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
 243 {
 244         /*  hz = cyc/(Billion ns)
 245          *  mult/2^shift  = ns/cyc
 246          *  mult = ns/cyc * 2^shift
 247          *  mult = 1Billion/hz * 2^shift
 248          *  mult = 1000000000 * 2^shift / hz
 249          *  mult = (1000000000<<shift) / hz
 250          */
 251         u64 tmp = ((u64)1000000000) << shift_constant;
 252
 253         tmp += hz/2; /* round for do_div */
 254         do_div(tmp, hz);
 255
 256         return (u32)tmp;
 257 }
 258
 259 /**
 260  * clocksource_cyc2ns - converts clocksource cycles to nanoseconds
 261  *
 262  * Converts cycles to nanoseconds, using the given mult and shift.
 263  *
 264  * XXX - This could use some mult_lxl_ll() asm optimization
 265  */
 266 static inline s64 clocksource_cyc2ns(cycle_t cycles, u32 mult, u32 shift)
 267 {
 268         return ((u64) cycles * mult) >> shift;
 269 }
 270
 271
 272 /* used to install a new clocksource */
 273 extern int clocksource_register(struct clocksource*);
 274 extern void clocksource_unregister(struct clocksource*);
 275 extern void clocksource_touch_watchdog(void);
 276 extern struct clocksource* clocksource_get_next(void);
 277 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 278 extern void clocksource_resume(void);
 279 extern struct clocksource * __init __weak clocksource_default_clock(void);
 280
 281 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
 282 extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
 283 extern void update_vsyscall_tz(void);
 284 #else
 285 static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
 286 {
 287 }
 288
 289 static inline void update_vsyscall_tz(void)
 290 {
 291 }
 292 #endif
 293
 294 extern void timekeeping_notify(struct clocksource *clock);
 295
 296 #endif /* _LINUX_CLOCKSOURCE_H */