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