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  * @resume:             resume function for the clocksource, if necessary
  52  * @cycle_interval:     Used internally by timekeeping core, please ignore.
  53  * @xtime_interval:     Used internally by timekeeping core, please ignore.
  54  */
  55 struct clocksource {
  56         char *name;
  57         struct list_head list;
  58         int rating;
  59         cycle_t (*read)(void);
  60         cycle_t mask;
  61         u32 mult;
  62         u32 shift;
  63         unsigned long flags;
  64         cycle_t (*vread)(void);
  65         void (*resume)(void);
  66
  67         /* timekeeping specific data, ignore */
  68         cycle_t cycle_last, cycle_interval;
  69         u64 xtime_nsec, xtime_interval;
  70         s64 error;
  71
  72 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
  73         /* Watchdog related data, used by the framework */
  74         struct list_head wd_list;
  75         cycle_t wd_last;
  76 #endif
  77 };
  78
  79 /*
  80  * Clock source flags bits::
  81  */
  82 #define CLOCK_SOURCE_IS_CONTINUOUS              0x01
  83 #define CLOCK_SOURCE_MUST_VERIFY                0x02
  84
  85 #define CLOCK_SOURCE_WATCHDOG                   0x10
  86 #define CLOCK_SOURCE_VALID_FOR_HRES             0x20
  87
  88 /* simplify initialization of mask field */
  89 #define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
  90
  91 /**
  92  * clocksource_khz2mult - calculates mult from khz and shift
  93  * @khz:                Clocksource frequency in KHz
  94  * @shift_constant:     Clocksource shift factor
  95  *
  96  * Helper functions that converts a khz counter frequency to a timsource
  97  * multiplier, given the clocksource shift value
  98  */
  99 static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
 100 {
 101         /*  khz = cyc/(Million ns)
 102          *  mult/2^shift  = ns/cyc
 103          *  mult = ns/cyc * 2^shift
 104          *  mult = 1Million/khz * 2^shift
 105          *  mult = 1000000 * 2^shift / khz
 106          *  mult = (1000000<<shift) / khz
 107          */
 108         u64 tmp = ((u64)1000000) << shift_constant;
 109
 110         tmp += khz/2; /* round for do_div */
 111         do_div(tmp, khz);
 112
 113         return (u32)tmp;
 114 }
 115
 116 /**
 117  * clocksource_hz2mult - calculates mult from hz and shift
 118  * @hz:                 Clocksource frequency in Hz
 119  * @shift_constant:     Clocksource shift factor
 120  *
 121  * Helper functions that converts a hz counter
 122  * frequency to a timsource multiplier, given the
 123  * clocksource shift value
 124  */
 125 static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
 126 {
 127         /*  hz = cyc/(Billion ns)
 128          *  mult/2^shift  = ns/cyc
 129          *  mult = ns/cyc * 2^shift
 130          *  mult = 1Billion/hz * 2^shift
 131          *  mult = 1000000000 * 2^shift / hz
 132          *  mult = (1000000000<<shift) / hz
 133          */
 134         u64 tmp = ((u64)1000000000) << shift_constant;
 135
 136         tmp += hz/2; /* round for do_div */
 137         do_div(tmp, hz);
 138
 139         return (u32)tmp;
 140 }
 141
 142 /**
 143  * clocksource_read: - Access the clocksource's current cycle value
 144  * @cs:         pointer to clocksource being read
 145  *
 146  * Uses the clocksource to return the current cycle_t value
 147  */
 148 static inline cycle_t clocksource_read(struct clocksource *cs)
 149 {
 150         return cs->read();
 151 }
 152
 153 /**
 154  * cyc2ns - converts clocksource cycles to nanoseconds
 155  * @cs:         Pointer to clocksource
 156  * @cycles:     Cycles
 157  *
 158  * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
 159  *
 160  * XXX - This could use some mult_lxl_ll() asm optimization
 161  */
 162 static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
 163 {
 164         u64 ret = (u64)cycles;
 165         ret = (ret * cs->mult) >> cs->shift;
 166         return ret;
 167 }
 168
 169 /**
 170  * clocksource_calculate_interval - Calculates a clocksource interval struct
 171  *
 172  * @c:          Pointer to clocksource.
 173  * @length_nsec: Desired interval length in nanoseconds.
 174  *
 175  * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
 176  * pair and interval request.
 177  *
 178  * Unless you're the timekeeping code, you should not be using this!
 179  */
 180 static inline void clocksource_calculate_interval(struct clocksource *c,
 181                                                   unsigned long length_nsec)
 182 {
 183         u64 tmp;
 184
 185         /* XXX - All of this could use a whole lot of optimization */
 186         tmp = length_nsec;
 187         tmp <<= c->shift;
 188         tmp += c->mult/2;
 189         do_div(tmp, c->mult);
 190
 191         c->cycle_interval = (cycle_t)tmp;
 192         if (c->cycle_interval == 0)
 193                 c->cycle_interval = 1;
 194
 195         c->xtime_interval = (u64)c->cycle_interval * c->mult;
 196 }
 197
 198
 199 /* used to install a new clocksource */
 200 extern int clocksource_register(struct clocksource*);
 201 extern struct clocksource* clocksource_get_next(void);
 202 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 203 extern void clocksource_resume(void);
 204
 205 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
 206 extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
 207 #else
 208 static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
 209 {
 210 }
 211 #endif
 212
 213 #endif /* _LINUX_CLOCKSOURCE_H */