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  * @cycle_interval:     Used internally by timekeeping core, please ignore.
  53  * @xtime_interval:     Used internally by timekeeping core, please ignore.
  54  */
  55 struct clocksource {
  56         /*
  57          * First part of structure is read mostly
  58          */
  59         char *name;
  60         struct list_head list;
  61         int rating;
  62         cycle_t (*read)(void);
  63         cycle_t mask;
  64         u32 mult;
  65         u32 shift;
  66         unsigned long flags;
  67         cycle_t (*vread)(void);
  68
  69         /* timekeeping specific data, ignore */
  70         cycle_t cycle_interval;
  71         u64     xtime_interval;
  72         /*
  73          * Second part is written at each timer interrupt
  74          * Keep it in a different cache line to dirty no
  75          * more than one cache line.
  76          */
  77         cycle_t cycle_last ____cacheline_aligned_in_smp;
  78         u64 xtime_nsec;
  79         s64 error;
  80
  81 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
  82         /* Watchdog related data, used by the framework */
  83         struct list_head wd_list;
  84         cycle_t wd_last;
  85 #endif
  86 };
  87
  88 /*
  89  * Clock source flags bits::
  90  */
  91 #define CLOCK_SOURCE_IS_CONTINUOUS              0x01
  92 #define CLOCK_SOURCE_MUST_VERIFY                0x02
  93
  94 #define CLOCK_SOURCE_WATCHDOG                   0x10
  95 #define CLOCK_SOURCE_VALID_FOR_HRES             0x20
  96
  97 /* simplify initialization of mask field */
  98 #define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
  99
 100 /**
 101  * clocksource_khz2mult - calculates mult from khz and shift
 102  * @khz:                Clocksource frequency in KHz
 103  * @shift_constant:     Clocksource shift factor
 104  *
 105  * Helper functions that converts a khz counter frequency to a timsource
 106  * multiplier, given the clocksource shift value
 107  */
 108 static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
 109 {
 110         /*  khz = cyc/(Million ns)
 111          *  mult/2^shift  = ns/cyc
 112          *  mult = ns/cyc * 2^shift
 113          *  mult = 1Million/khz * 2^shift
 114          *  mult = 1000000 * 2^shift / khz
 115          *  mult = (1000000<<shift) / khz
 116          */
 117         u64 tmp = ((u64)1000000) << shift_constant;
 118
 119         tmp += khz/2; /* round for do_div */
 120         do_div(tmp, khz);
 121
 122         return (u32)tmp;
 123 }
 124
 125 /**
 126  * clocksource_hz2mult - calculates mult from hz and shift
 127  * @hz:                 Clocksource frequency in Hz
 128  * @shift_constant:     Clocksource shift factor
 129  *
 130  * Helper functions that converts a hz counter
 131  * frequency to a timsource multiplier, given the
 132  * clocksource shift value
 133  */
 134 static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
 135 {
 136         /*  hz = cyc/(Billion ns)
 137          *  mult/2^shift  = ns/cyc
 138          *  mult = ns/cyc * 2^shift
 139          *  mult = 1Billion/hz * 2^shift
 140          *  mult = 1000000000 * 2^shift / hz
 141          *  mult = (1000000000<<shift) / hz
 142          */
 143         u64 tmp = ((u64)1000000000) << shift_constant;
 144
 145         tmp += hz/2; /* round for do_div */
 146         do_div(tmp, hz);
 147
 148         return (u32)tmp;
 149 }
 150
 151 /**
 152  * clocksource_read: - Access the clocksource's current cycle value
 153  * @cs:         pointer to clocksource being read
 154  *
 155  * Uses the clocksource to return the current cycle_t value
 156  */
 157 static inline cycle_t clocksource_read(struct clocksource *cs)
 158 {
 159         return cs->read();
 160 }
 161
 162 /**
 163  * cyc2ns - converts clocksource cycles to nanoseconds
 164  * @cs:         Pointer to clocksource
 165  * @cycles:     Cycles
 166  *
 167  * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
 168  *
 169  * XXX - This could use some mult_lxl_ll() asm optimization
 170  */
 171 static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
 172 {
 173         u64 ret = (u64)cycles;
 174         ret = (ret * cs->mult) >> cs->shift;
 175         return ret;
 176 }
 177
 178 /**
 179  * clocksource_calculate_interval - Calculates a clocksource interval struct
 180  *
 181  * @c:          Pointer to clocksource.
 182  * @length_nsec: Desired interval length in nanoseconds.
 183  *
 184  * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
 185  * pair and interval request.
 186  *
 187  * Unless you're the timekeeping code, you should not be using this!
 188  */
 189 static inline void clocksource_calculate_interval(struct clocksource *c,
 190                                                   unsigned long length_nsec)
 191 {
 192         u64 tmp;
 193
 194         /* XXX - All of this could use a whole lot of optimization */
 195         tmp = length_nsec;
 196         tmp <<= c->shift;
 197         tmp += c->mult/2;
 198         do_div(tmp, c->mult);
 199
 200         c->cycle_interval = (cycle_t)tmp;
 201         if (c->cycle_interval == 0)
 202                 c->cycle_interval = 1;
 203
 204         c->xtime_interval = (u64)c->cycle_interval * c->mult;
 205 }
 206
 207
 208 /* used to install a new clocksource */
 209 extern int clocksource_register(struct clocksource*);
 210 extern struct clocksource* clocksource_get_next(void);
 211 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 212
 213 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
 214 extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
 215 #else
 216 static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
 217 {
 218 }
 219 #endif
 220
 221 #endif /* _LINUX_CLOCKSOURCE_H */