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/timer.h>
  16 #include <asm/div64.h>
  17 #include <asm/io.h>
  18
  19 /* clocksource cycle base type */
  20 typedef u64 cycle_t;
  21 struct clocksource;
  22
  23 /**
  24  * struct clocksource - hardware abstraction for a free running counter
  25  *      Provides mostly state-free accessors to the underlying hardware.
  26  *
  27  * @name:               ptr to clocksource name
  28  * @list:               list head for registration
  29  * @rating:             rating value for selection (higher is better)
  30  *                      To avoid rating inflation the following
  31  *                      list should give you a guide as to how
  32  *                      to assign your clocksource a rating
  33  *                      1-99: Unfit for real use
  34  *                              Only available for bootup and testing purposes.
  35  *                      100-199: Base level usability.
  36  *                              Functional for real use, but not desired.
  37  *                      200-299: Good.
  38  *                              A correct and usable clocksource.
  39  *                      300-399: Desired.
  40  *                              A reasonably fast and accurate clocksource.
  41  *                      400-499: Perfect
  42  *                              The ideal clocksource. A must-use where
  43  *                              available.
  44  * @read:               returns a cycle value
  45  * @mask:               bitmask for two's complement
  46  *                      subtraction of non 64 bit counters
  47  * @mult:               cycle to nanosecond multiplier
  48  * @shift:              cycle to nanosecond divisor (power of two)
  49  * @flags:              flags describing special properties
  50  * @vread:              vsyscall based read
  51  * @cycle_interval:     Used internally by timekeeping core, please ignore.
  52  * @xtime_interval:     Used internally by timekeeping core, please ignore.
  53  */
  54 struct clocksource {
  55         char *name;
  56         struct list_head list;
  57         int rating;
  58         cycle_t (*read)(void);
  59         cycle_t mask;
  60         u32 mult;
  61         u32 shift;
  62         unsigned long flags;
  63         cycle_t (*vread)(void);
  64
  65         /* timekeeping specific data, ignore */
  66         cycle_t cycle_last, cycle_interval;
  67         u64 xtime_nsec, xtime_interval;
  68         s64 error;
  69
  70 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
  71         /* Watchdog related data, used by the framework */
  72         struct list_head wd_list;
  73         cycle_t wd_last;
  74 #endif
  75 };
  76
  77 /*
  78  * Clock source flags bits::
  79  */
  80 #define CLOCK_SOURCE_IS_CONTINUOUS              0x01
  81 #define CLOCK_SOURCE_MUST_VERIFY                0x02
  82
  83 #define CLOCK_SOURCE_WATCHDOG                   0x10
  84 #define CLOCK_SOURCE_VALID_FOR_HRES             0x20
  85
  86 /* simplify initialization of mask field */
  87 #define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
  88
  89 /**
  90  * clocksource_khz2mult - calculates mult from khz and shift
  91  * @khz:                Clocksource frequency in KHz
  92  * @shift_constant:     Clocksource shift factor
  93  *
  94  * Helper functions that converts a khz counter frequency to a timsource
  95  * multiplier, given the clocksource shift value
  96  */
  97 static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
  98 {
  99         /*  khz = cyc/(Million ns)
 100          *  mult/2^shift  = ns/cyc
 101          *  mult = ns/cyc * 2^shift
 102          *  mult = 1Million/khz * 2^shift
 103          *  mult = 1000000 * 2^shift / khz
 104          *  mult = (1000000<<shift) / khz
 105          */
 106         u64 tmp = ((u64)1000000) << shift_constant;
 107
 108         tmp += khz/2; /* round for do_div */
 109         do_div(tmp, khz);
 110
 111         return (u32)tmp;
 112 }
 113
 114 /**
 115  * clocksource_hz2mult - calculates mult from hz and shift
 116  * @hz:                 Clocksource frequency in Hz
 117  * @shift_constant:     Clocksource shift factor
 118  *
 119  * Helper functions that converts a hz counter
 120  * frequency to a timsource multiplier, given the
 121  * clocksource shift value
 122  */
 123 static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
 124 {
 125         /*  hz = cyc/(Billion ns)
 126          *  mult/2^shift  = ns/cyc
 127          *  mult = ns/cyc * 2^shift
 128          *  mult = 1Billion/hz * 2^shift
 129          *  mult = 1000000000 * 2^shift / hz
 130          *  mult = (1000000000<<shift) / hz
 131          */
 132         u64 tmp = ((u64)1000000000) << shift_constant;
 133
 134         tmp += hz/2; /* round for do_div */
 135         do_div(tmp, hz);
 136
 137         return (u32)tmp;
 138 }
 139
 140 /**
 141  * clocksource_read: - Access the clocksource's current cycle value
 142  * @cs:         pointer to clocksource being read
 143  *
 144  * Uses the clocksource to return the current cycle_t value
 145  */
 146 static inline cycle_t clocksource_read(struct clocksource *cs)
 147 {
 148         return cs->read();
 149 }
 150
 151 /**
 152  * cyc2ns - converts clocksource cycles to nanoseconds
 153  * @cs:         Pointer to clocksource
 154  * @cycles:     Cycles
 155  *
 156  * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
 157  *
 158  * XXX - This could use some mult_lxl_ll() asm optimization
 159  */
 160 static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
 161 {
 162         u64 ret = (u64)cycles;
 163         ret = (ret * cs->mult) >> cs->shift;
 164         return ret;
 165 }
 166
 167 /**
 168  * clocksource_calculate_interval - Calculates a clocksource interval struct
 169  *
 170  * @c:          Pointer to clocksource.
 171  * @length_nsec: Desired interval length in nanoseconds.
 172  *
 173  * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
 174  * pair and interval request.
 175  *
 176  * Unless you're the timekeeping code, you should not be using this!
 177  */
 178 static inline void clocksource_calculate_interval(struct clocksource *c,
 179                                                   unsigned long length_nsec)
 180 {
 181         u64 tmp;
 182
 183         /* XXX - All of this could use a whole lot of optimization */
 184         tmp = length_nsec;
 185         tmp <<= c->shift;
 186         tmp += c->mult/2;
 187         do_div(tmp, c->mult);
 188
 189         c->cycle_interval = (cycle_t)tmp;
 190         if (c->cycle_interval == 0)
 191                 c->cycle_interval = 1;
 192
 193         c->xtime_interval = (u64)c->cycle_interval * c->mult;
 194 }
 195
 196
 197 /* used to install a new clocksource */
 198 extern int clocksource_register(struct clocksource*);
 199 extern struct clocksource* clocksource_get_next(void);
 200 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 201
 202 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
 203 extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
 204 #else
 205 static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
 206 {
 207 }
 208 #endif
 209
 210 #endif /* _LINUX_CLOCKSOURCE_H */