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 */ 222