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  * @cycle_interval:     Used internally by timekeeping core, please ignore.
  51  * @xtime_interval:     Used internally by timekeeping core, please ignore.
  52  */
  53 struct clocksource {
  54         char *name;
  55         struct list_head list;
  56         int rating;
  57         cycle_t (*read)(void);
  58         cycle_t mask;
  59         u32 mult;
  60         u32 shift;
  61         unsigned long flags;
  62
  63         /* timekeeping specific data, ignore */
  64         cycle_t cycle_last, cycle_interval;
  65         u64 xtime_nsec, xtime_interval;
  66         s64 error;
  67
  68 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
  69         /* Watchdog related data, used by the framework */
  70         struct list_head wd_list;
  71         cycle_t wd_last;
  72 #endif
  73 };
  74
  75 /*
  76  * Clock source flags bits::
  77  */
  78 #define CLOCK_SOURCE_IS_CONTINUOUS              0x01
  79 #define CLOCK_SOURCE_MUST_VERIFY                0x02
  80
  81 #define CLOCK_SOURCE_WATCHDOG                   0x10
  82 #define CLOCK_SOURCE_VALID_FOR_HRES             0x20
  83
  84 /* simplify initialization of mask field */
  85 #define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
  86
  87 /**
  88  * clocksource_khz2mult - calculates mult from khz and shift
  89  * @khz:                Clocksource frequency in KHz
  90  * @shift_constant:     Clocksource shift factor
  91  *
  92  * Helper functions that converts a khz counter frequency to a timsource
  93  * multiplier, given the clocksource shift value
  94  */
  95 static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
  96 {
  97         /*  khz = cyc/(Million ns)
  98          *  mult/2^shift  = ns/cyc
  99          *  mult = ns/cyc * 2^shift
 100          *  mult = 1Million/khz * 2^shift
 101          *  mult = 1000000 * 2^shift / khz
 102          *  mult = (1000000<<shift) / khz
 103          */
 104         u64 tmp = ((u64)1000000) << shift_constant;
 105
 106         tmp += khz/2; /* round for do_div */
 107         do_div(tmp, khz);
 108
 109         return (u32)tmp;
 110 }
 111
 112 /**
 113  * clocksource_hz2mult - calculates mult from hz and shift
 114  * @hz:                 Clocksource frequency in Hz
 115  * @shift_constant:     Clocksource shift factor
 116  *
 117  * Helper functions that converts a hz counter
 118  * frequency to a timsource multiplier, given the
 119  * clocksource shift value
 120  */
 121 static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
 122 {
 123         /*  hz = cyc/(Billion ns)
 124          *  mult/2^shift  = ns/cyc
 125          *  mult = ns/cyc * 2^shift
 126          *  mult = 1Billion/hz * 2^shift
 127          *  mult = 1000000000 * 2^shift / hz
 128          *  mult = (1000000000<<shift) / hz
 129          */
 130         u64 tmp = ((u64)1000000000) << shift_constant;
 131
 132         tmp += hz/2; /* round for do_div */
 133         do_div(tmp, hz);
 134
 135         return (u32)tmp;
 136 }
 137
 138 /**
 139  * clocksource_read: - Access the clocksource's current cycle value
 140  * @cs:         pointer to clocksource being read
 141  *
 142  * Uses the clocksource to return the current cycle_t value
 143  */
 144 static inline cycle_t clocksource_read(struct clocksource *cs)
 145 {
 146         return cs->read();
 147 }
 148
 149 /**
 150  * cyc2ns - converts clocksource cycles to nanoseconds
 151  * @cs:         Pointer to clocksource
 152  * @cycles:     Cycles
 153  *
 154  * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
 155  *
 156  * XXX - This could use some mult_lxl_ll() asm optimization
 157  */
 158 static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
 159 {
 160         u64 ret = (u64)cycles;
 161         ret = (ret * cs->mult) >> cs->shift;
 162         return ret;
 163 }
 164
 165 /**
 166  * clocksource_calculate_interval - Calculates a clocksource interval struct
 167  *
 168  * @c:          Pointer to clocksource.
 169  * @length_nsec: Desired interval length in nanoseconds.
 170  *
 171  * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
 172  * pair and interval request.
 173  *
 174  * Unless you're the timekeeping code, you should not be using this!
 175  */
 176 static inline void clocksource_calculate_interval(struct clocksource *c,
 177                                                   unsigned long length_nsec)
 178 {
 179         u64 tmp;
 180
 181         /* XXX - All of this could use a whole lot of optimization */
 182         tmp = length_nsec;
 183         tmp <<= c->shift;
 184         tmp += c->mult/2;
 185         do_div(tmp, c->mult);
 186
 187         c->cycle_interval = (cycle_t)tmp;
 188         if (c->cycle_interval == 0)
 189                 c->cycle_interval = 1;
 190
 191         c->xtime_interval = (u64)c->cycle_interval * c->mult;
 192 }
 193
 194
 195 /* used to install a new clocksource */
 196 extern int clocksource_register(struct clocksource*);
 197 extern struct clocksource* clocksource_get_next(void);
 198 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 199
 200 #endif /* _LINUX_CLOCKSOURCE_H */