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 extern struct clocksource *clock;       /* current clocksource */
  97
  98 /*
  99  * Clock source flags bits::
 100  */
 101 #define CLOCK_SOURCE_IS_CONTINUOUS              0x01
 102 #define CLOCK_SOURCE_MUST_VERIFY                0x02
 103
 104 #define CLOCK_SOURCE_WATCHDOG                   0x10
 105 #define CLOCK_SOURCE_VALID_FOR_HRES             0x20
 106
 107 /* simplify initialization of mask field */
 108 #define CLOCKSOURCE_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
 109
 110 /**
 111  * clocksource_khz2mult - calculates mult from khz and shift
 112  * @khz:                Clocksource frequency in KHz
 113  * @shift_constant:     Clocksource shift factor
 114  *
 115  * Helper functions that converts a khz counter frequency to a timsource
 116  * multiplier, given the clocksource shift value
 117  */
 118 static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
 119 {
 120         /*  khz = cyc/(Million ns)
 121          *  mult/2^shift  = ns/cyc
 122          *  mult = ns/cyc * 2^shift
 123          *  mult = 1Million/khz * 2^shift
 124          *  mult = 1000000 * 2^shift / khz
 125          *  mult = (1000000<<shift) / khz
 126          */
 127         u64 tmp = ((u64)1000000) << shift_constant;
 128
 129         tmp += khz/2; /* round for do_div */
 130         do_div(tmp, khz);
 131
 132         return (u32)tmp;
 133 }
 134
 135 /**
 136  * clocksource_hz2mult - calculates mult from hz and shift
 137  * @hz:                 Clocksource frequency in Hz
 138  * @shift_constant:     Clocksource shift factor
 139  *
 140  * Helper functions that converts a hz counter
 141  * frequency to a timsource multiplier, given the
 142  * clocksource shift value
 143  */
 144 static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
 145 {
 146         /*  hz = cyc/(Billion ns)
 147          *  mult/2^shift  = ns/cyc
 148          *  mult = ns/cyc * 2^shift
 149          *  mult = 1Billion/hz * 2^shift
 150          *  mult = 1000000000 * 2^shift / hz
 151          *  mult = (1000000000<<shift) / hz
 152          */
 153         u64 tmp = ((u64)1000000000) << shift_constant;
 154
 155         tmp += hz/2; /* round for do_div */
 156         do_div(tmp, hz);
 157
 158         return (u32)tmp;
 159 }
 160
 161 /**
 162  * clocksource_read: - Access the clocksource's current cycle value
 163  * @cs:         pointer to clocksource being read
 164  *
 165  * Uses the clocksource to return the current cycle_t value
 166  */
 167 static inline cycle_t clocksource_read(struct clocksource *cs)
 168 {
 169         return cs->read();
 170 }
 171
 172 /**
 173  * cyc2ns - converts clocksource cycles to nanoseconds
 174  * @cs:         Pointer to clocksource
 175  * @cycles:     Cycles
 176  *
 177  * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
 178  *
 179  * XXX - This could use some mult_lxl_ll() asm optimization
 180  */
 181 static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
 182 {
 183         u64 ret = (u64)cycles;
 184         ret = (ret * cs->mult) >> cs->shift;
 185         return ret;
 186 }
 187
 188 /**
 189  * clocksource_calculate_interval - Calculates a clocksource interval struct
 190  *
 191  * @c:          Pointer to clocksource.
 192  * @length_nsec: Desired interval length in nanoseconds.
 193  *
 194  * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
 195  * pair and interval request.
 196  *
 197  * Unless you're the timekeeping code, you should not be using this!
 198  */
 199 static inline void clocksource_calculate_interval(struct clocksource *c,
 200                                                   unsigned long length_nsec)
 201 {
 202         u64 tmp;
 203
 204         /* XXX - All of this could use a whole lot of optimization */
 205         tmp = length_nsec;
 206         tmp <<= c->shift;
 207         tmp += c->mult/2;
 208         do_div(tmp, c->mult);
 209
 210         c->cycle_interval = (cycle_t)tmp;
 211         if (c->cycle_interval == 0)
 212                 c->cycle_interval = 1;
 213
 214         c->xtime_interval = (u64)c->cycle_interval * c->mult;
 215 }
 216
 217
 218 /* used to install a new clocksource */
 219 extern int clocksource_register(struct clocksource*);
 220 extern void clocksource_unregister(struct clocksource*);
 221 extern void clocksource_touch_watchdog(void);
 222 extern struct clocksource* clocksource_get_next(void);
 223 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 224 extern void clocksource_resume(void);
 225
 226 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
 227 extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
 228 extern void update_vsyscall_tz(void);
 229 #else
 230 static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
 231 {
 232 }
 233
 234 static inline void update_vsyscall_tz(void)
 235 {
 236 }
 237 #endif
 238
 239 #endif /* _LINUX_CLOCKSOURCE_H */