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 */ 225