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 <asm/div64.h>
  18 #include <asm/io.h>
  19
  20 /* clocksource cycle base type */
  21 typedef u64 cycle_t;
  22 struct clocksource;
  23
  24 /**
  25  * struct clocksource - hardware abstraction for a free running counter
  26  *      Provides mostly state-free accessors to the underlying hardware.
  27  *
  28  * @name:               ptr to clocksource name
  29  * @list:               list head for registration
  30  * @rating:             rating value for selection (higher is better)
  31  *                      To avoid rating inflation the following
  32  *                      list should give you a guide as to how
  33  *                      to assign your clocksource a rating
  34  *                      1-99: Unfit for real use
  35  *                              Only available for bootup and testing purposes.
  36  *                      100-199: Base level usability.
  37  *                              Functional for real use, but not desired.
  38  *                      200-299: Good.
  39  *                              A correct and usable clocksource.
  40  *                      300-399: Desired.
  41  *                              A reasonably fast and accurate clocksource.
  42  *                      400-499: Perfect
  43  *                              The ideal clocksource. A must-use where
  44  *                              available.
  45  * @read:               returns a cycle value
  46  * @mask:               bitmask for two's complement
  47  *                      subtraction of non 64 bit counters
  48  * @mult:               cycle to nanosecond multiplier
  49  * @shift:              cycle to nanosecond divisor (power of two)
  50  * @flags:              flags describing special properties
  51  * @vread:              vsyscall based read
  52  * @resume:             resume function for the clocksource, if necessary
  53  * @cycle_interval:     Used internally by timekeeping core, please ignore.
  54  * @xtime_interval:     Used internally by timekeeping core, please ignore.
  55  */
  56 struct clocksource {
  57         /*
  58          * First part of structure is read mostly
  59          */
  60         char *name;
  61         struct list_head list;
  62         int rating;
  63         cycle_t (*read)(void);
  64         cycle_t mask;
  65         u32 mult;
  66         u32 shift;
  67         unsigned long flags;
  68         cycle_t (*vread)(void);
  69         void (*resume)(void);
  70 #ifdef CONFIG_IA64
  71         void *fsys_mmio;        /* used by fsyscall asm code */
  72 #define CLKSRC_FSYS_MMIO_SET(mmio, addr)      ((mmio) = (addr))
  73 #else
  74 #define CLKSRC_FSYS_MMIO_SET(mmio, addr)      do { } while (0)
  75 #endif
  76
  77         /* timekeeping specific data, ignore */
  78         cycle_t cycle_interval;
  79         u64     xtime_interval;
  80         /*
  81          * Second part is written at each timer interrupt
  82          * Keep it in a different cache line to dirty no
  83          * more than one cache line.
  84          */
  85         cycle_t cycle_last ____cacheline_aligned_in_smp;
  86         u64 xtime_nsec;
  87         s64 error;
  88
  89 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
  90         /* Watchdog related data, used by the framework */
  91         struct list_head wd_list;
  92         cycle_t wd_last;
  93 #endif
  94 };
  95
  96 /*
  97  * Clock source flags bits::
  98  */
  99 #define CLOCK_SOURCE_IS_CONTINUOUS              0x01
 100 #define CLOCK_SOURCE_MUST_VERIFY                0x02
 101
 102 #define CLOCK_SOURCE_WATCHDOG                   0x10
 103 #define CLOCK_SOURCE_VALID_FOR_HRES             0x20
 104
 105 /* simplify initialization of mask field */
 106 #define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
 107
 108 /**
 109  * clocksource_khz2mult - calculates mult from khz and shift
 110  * @khz:                Clocksource frequency in KHz
 111  * @shift_constant:     Clocksource shift factor
 112  *
 113  * Helper functions that converts a khz counter frequency to a timsource
 114  * multiplier, given the clocksource shift value
 115  */
 116 static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
 117 {
 118         /*  khz = cyc/(Million ns)
 119          *  mult/2^shift  = ns/cyc
 120          *  mult = ns/cyc * 2^shift
 121          *  mult = 1Million/khz * 2^shift
 122          *  mult = 1000000 * 2^shift / khz
 123          *  mult = (1000000<<shift) / khz
 124          */
 125         u64 tmp = ((u64)1000000) << shift_constant;
 126
 127         tmp += khz/2; /* round for do_div */
 128         do_div(tmp, khz);
 129
 130         return (u32)tmp;
 131 }
 132
 133 /**
 134  * clocksource_hz2mult - calculates mult from hz and shift
 135  * @hz:                 Clocksource frequency in Hz
 136  * @shift_constant:     Clocksource shift factor
 137  *
 138  * Helper functions that converts a hz counter
 139  * frequency to a timsource multiplier, given the
 140  * clocksource shift value
 141  */
 142 static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
 143 {
 144         /*  hz = cyc/(Billion ns)
 145          *  mult/2^shift  = ns/cyc
 146          *  mult = ns/cyc * 2^shift
 147          *  mult = 1Billion/hz * 2^shift
 148          *  mult = 1000000000 * 2^shift / hz
 149          *  mult = (1000000000<<shift) / hz
 150          */
 151         u64 tmp = ((u64)1000000000) << shift_constant;
 152
 153         tmp += hz/2; /* round for do_div */
 154         do_div(tmp, hz);
 155
 156         return (u32)tmp;
 157 }
 158
 159 /**
 160  * clocksource_read: - Access the clocksource's current cycle value
 161  * @cs:         pointer to clocksource being read
 162  *
 163  * Uses the clocksource to return the current cycle_t value
 164  */
 165 static inline cycle_t clocksource_read(struct clocksource *cs)
 166 {
 167         return cs->read();
 168 }
 169
 170 /**
 171  * cyc2ns - converts clocksource cycles to nanoseconds
 172  * @cs:         Pointer to clocksource
 173  * @cycles:     Cycles
 174  *
 175  * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
 176  *
 177  * XXX - This could use some mult_lxl_ll() asm optimization
 178  */
 179 static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
 180 {
 181         u64 ret = (u64)cycles;
 182         ret = (ret * cs->mult) >> cs->shift;
 183         return ret;
 184 }
 185
 186 /**
 187  * clocksource_calculate_interval - Calculates a clocksource interval struct
 188  *
 189  * @c:          Pointer to clocksource.
 190  * @length_nsec: Desired interval length in nanoseconds.
 191  *
 192  * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
 193  * pair and interval request.
 194  *
 195  * Unless you're the timekeeping code, you should not be using this!
 196  */
 197 static inline void clocksource_calculate_interval(struct clocksource *c,
 198                                                   unsigned long length_nsec)
 199 {
 200         u64 tmp;
 201
 202         /* XXX - All of this could use a whole lot of optimization */
 203         tmp = length_nsec;
 204         tmp <<= c->shift;
 205         tmp += c->mult/2;
 206         do_div(tmp, c->mult);
 207
 208         c->cycle_interval = (cycle_t)tmp;
 209         if (c->cycle_interval == 0)
 210                 c->cycle_interval = 1;
 211
 212         c->xtime_interval = (u64)c->cycle_interval * c->mult;
 213 }
 214
 215
 216 /* used to install a new clocksource */
 217 extern int clocksource_register(struct clocksource*);
 218 extern struct clocksource* clocksource_get_next(void);
 219 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 220 extern void clocksource_resume(void);
 221
 222 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
 223 extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
 224 #else
 225 static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
 226 {
 227 }
 228 #endif
 229
 230 #endif /* _LINUX_CLOCKSOURCE_H */