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Diffstat (limited to 'include/linux/clocksource.h')
| -rw-r--r-- | include/linux/clocksource.h | 185 |
1 files changed, 185 insertions, 0 deletions
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h new file mode 100644 index 000000000000..d852024ed095 --- /dev/null +++ b/include/linux/clocksource.h @@ -0,0 +1,185 @@ +/* linux/include/linux/clocksource.h + * + * This file contains the structure definitions for clocksources. + * + * If you are not a clocksource, or timekeeping code, you should + * not be including this file! + */ +#ifndef _LINUX_CLOCKSOURCE_H +#define _LINUX_CLOCKSOURCE_H + +#include <linux/types.h> +#include <linux/timex.h> +#include <linux/time.h> +#include <linux/list.h> +#include <asm/div64.h> +#include <asm/io.h> + +/* clocksource cycle base type */ +typedef u64 cycle_t; + +/** + * struct clocksource - hardware abstraction for a free running counter + * Provides mostly state-free accessors to the underlying hardware. + * + * @name: ptr to clocksource name + * @list: list head for registration + * @rating: rating value for selection (higher is better) + * To avoid rating inflation the following + * list should give you a guide as to how + * to assign your clocksource a rating + * 1-99: Unfit for real use + * Only available for bootup and testing purposes. + * 100-199: Base level usability. + * Functional for real use, but not desired. + * 200-299: Good. + * A correct and usable clocksource. + * 300-399: Desired. + * A reasonably fast and accurate clocksource. + * 400-499: Perfect + * The ideal clocksource. A must-use where + * available. + * @read: returns a cycle value + * @mask: bitmask for two's complement + * subtraction of non 64 bit counters + * @mult: cycle to nanosecond multiplier + * @shift: cycle to nanosecond divisor (power of two) + * @update_callback: called when safe to alter clocksource values + * @is_continuous: defines if clocksource is free-running. + * @cycle_interval: Used internally by timekeeping core, please ignore. + * @xtime_interval: Used internally by timekeeping core, please ignore. + */ +struct clocksource { + char *name; + struct list_head list; + int rating; + cycle_t (*read)(void); + cycle_t mask; + u32 mult; + u32 shift; + int (*update_callback)(void); + int is_continuous; + + /* timekeeping specific data, ignore */ + cycle_t cycle_last, cycle_interval; + u64 xtime_nsec, xtime_interval; + s64 error; +}; + +/* simplify initialization of mask field */ +#define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1) + +/** + * clocksource_khz2mult - calculates mult from khz and shift + * @khz: Clocksource frequency in KHz + * @shift_constant: Clocksource shift factor + * + * Helper functions that converts a khz counter frequency to a timsource + * multiplier, given the clocksource shift value + */ +static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant) +{ + /* khz = cyc/(Million ns) + * mult/2^shift = ns/cyc + * mult = ns/cyc * 2^shift + * mult = 1Million/khz * 2^shift + * mult = 1000000 * 2^shift / khz + * mult = (1000000<<shift) / khz + */ + u64 tmp = ((u64)1000000) << shift_constant; + + tmp += khz/2; /* round for do_div */ + do_div(tmp, khz); + + return (u32)tmp; +} + +/** + * clocksource_hz2mult - calculates mult from hz and shift + * @hz: Clocksource frequency in Hz + * @shift_constant: Clocksource shift factor + * + * Helper functions that converts a hz counter + * frequency to a timsource multiplier, given the + * clocksource shift value + */ +static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant) +{ + /* hz = cyc/(Billion ns) + * mult/2^shift = ns/cyc + * mult = ns/cyc * 2^shift + * mult = 1Billion/hz * 2^shift + * mult = 1000000000 * 2^shift / hz + * mult = (1000000000<<shift) / hz + */ + u64 tmp = ((u64)1000000000) << shift_constant; + + tmp += hz/2; /* round for do_div */ + do_div(tmp, hz); + + return (u32)tmp; +} + +/** + * clocksource_read: - Access the clocksource's current cycle value + * @cs: pointer to clocksource being read + * + * Uses the clocksource to return the current cycle_t value + */ +static inline cycle_t clocksource_read(struct clocksource *cs) +{ + return cs->read(); +} + +/** + * cyc2ns - converts clocksource cycles to nanoseconds + * @cs: Pointer to clocksource + * @cycles: Cycles + * + * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds. + * + * XXX - This could use some mult_lxl_ll() asm optimization + */ +static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles) +{ + u64 ret = (u64)cycles; + ret = (ret * cs->mult) >> cs->shift; + return ret; +} + +/** + * clocksource_calculate_interval - Calculates a clocksource interval struct + * + * @c: Pointer to clocksource. + * @length_nsec: Desired interval length in nanoseconds. + * + * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment + * pair and interval request. + * + * Unless you're the timekeeping code, you should not be using this! + */ +static inline void clocksource_calculate_interval(struct clocksource *c, + unsigned long length_nsec) +{ + u64 tmp; + + /* XXX - All of this could use a whole lot of optimization */ + tmp = length_nsec; + tmp <<= c->shift; + tmp += c->mult/2; + do_div(tmp, c->mult); + + c->cycle_interval = (cycle_t)tmp; + if (c->cycle_interval == 0) + c->cycle_interval = 1; + + c->xtime_interval = (u64)c->cycle_interval * c->mult; +} + + +/* used to install a new clocksource */ +int clocksource_register(struct clocksource*); +void clocksource_reselect(void); +struct clocksource* clocksource_get_next(void); + +#endif /* _LINUX_CLOCKSOURCE_H */ |