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
  71         /* timekeeping specific data, ignore */
  72         cycle_t cycle_interval;
  73         u64     xtime_interval;
  74         /*
  75          * Second part is written at each timer interrupt
  76          * Keep it in a different cache line to dirty no
  77          * more than one cache line.
  78          */
  79         cycle_t cycle_last ____cacheline_aligned_in_smp;
  80         u64 xtime_nsec;
  81         s64 error;
  82
  83 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
  84         /* Watchdog related data, used by the framework */
  85         struct list_head wd_list;
  86         cycle_t wd_last;
  87 #endif
  88 };
  89
  90 /*
  91  * Clock source flags bits::
  92  */
  93 #define CLOCK_SOURCE_IS_CONTINUOUS              0x01
  94 #define CLOCK_SOURCE_MUST_VERIFY                0x02
  95
  96 #define CLOCK_SOURCE_WATCHDOG                   0x10
  97 #define CLOCK_SOURCE_VALID_FOR_HRES             0x20
  98
  99 /* simplify initialization of mask field */
 100 #define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
 101
 102 /**
 103  * clocksource_khz2mult - calculates mult from khz and shift
 104  * @khz:                Clocksource frequency in KHz
 105  * @shift_constant:     Clocksource shift factor
 106  *
 107  * Helper functions that converts a khz counter frequency to a timsource
 108  * multiplier, given the clocksource shift value
 109  */
 110 static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
 111 {
 112         /*  khz = cyc/(Million ns)
 113          *  mult/2^shift  = ns/cyc
 114          *  mult = ns/cyc * 2^shift
 115          *  mult = 1Million/khz * 2^shift
 116          *  mult = 1000000 * 2^shift / khz
 117          *  mult = (1000000<<shift) / khz
 118          */
 119         u64 tmp = ((u64)1000000) << shift_constant;
 120
 121         tmp += khz/2; /* round for do_div */
 122         do_div(tmp, khz);
 123
 124         return (u32)tmp;
 125 }
 126
 127 /**
 128  * clocksource_hz2mult - calculates mult from hz and shift
 129  * @hz:                 Clocksource frequency in Hz
 130  * @shift_constant:     Clocksource shift factor
 131  *
 132  * Helper functions that converts a hz counter
 133  * frequency to a timsource multiplier, given the
 134  * clocksource shift value
 135  */
 136 static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
 137 {
 138         /*  hz = cyc/(Billion ns)
 139          *  mult/2^shift  = ns/cyc
 140          *  mult = ns/cyc * 2^shift
 141          *  mult = 1Billion/hz * 2^shift
 142          *  mult = 1000000000 * 2^shift / hz
 143          *  mult = (1000000000<<shift) / hz
 144          */
 145         u64 tmp = ((u64)1000000000) << shift_constant;
 146
 147         tmp += hz/2; /* round for do_div */
 148         do_div(tmp, hz);
 149
 150         return (u32)tmp;
 151 }
 152
 153 /**
 154  * clocksource_read: - Access the clocksource's current cycle value
 155  * @cs:         pointer to clocksource being read
 156  *
 157  * Uses the clocksource to return the current cycle_t value
 158  */
 159 static inline cycle_t clocksource_read(struct clocksource *cs)
 160 {
 161         return cs->read();
 162 }
 163
 164 /**
 165  * cyc2ns - converts clocksource cycles to nanoseconds
 166  * @cs:         Pointer to clocksource
 167  * @cycles:     Cycles
 168  *
 169  * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
 170  *
 171  * XXX - This could use some mult_lxl_ll() asm optimization
 172  */
 173 static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
 174 {
 175         u64 ret = (u64)cycles;
 176         ret = (ret * cs->mult) >> cs->shift;
 177         return ret;
 178 }
 179
 180 /**
 181  * clocksource_calculate_interval - Calculates a clocksource interval struct
 182  *
 183  * @c:          Pointer to clocksource.
 184  * @length_nsec: Desired interval length in nanoseconds.
 185  *
 186  * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
 187  * pair and interval request.
 188  *
 189  * Unless you're the timekeeping code, you should not be using this!
 190  */
 191 static inline void clocksource_calculate_interval(struct clocksource *c,
 192                                                   unsigned long length_nsec)
 193 {
 194         u64 tmp;
 195
 196         /* XXX - All of this could use a whole lot of optimization */
 197         tmp = length_nsec;
 198         tmp <<= c->shift;
 199         tmp += c->mult/2;
 200         do_div(tmp, c->mult);
 201
 202         c->cycle_interval = (cycle_t)tmp;
 203         if (c->cycle_interval == 0)
 204                 c->cycle_interval = 1;
 205
 206         c->xtime_interval = (u64)c->cycle_interval * c->mult;
 207 }
 208
 209
 210 /* used to install a new clocksource */
 211 extern int clocksource_register(struct clocksource*);
 212 extern struct clocksource* clocksource_get_next(void);
 213 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 214 extern void clocksource_resume(void);
 215
 216 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
 217 extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
 218 #else
 219 static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
 220 {
 221 }
 222 #endif
 223
 224 #endif /* _LINUX_CLOCKSOURCE_H */