From 734efb467b31e56c2f9430590a9aa867ecf3eea1 Mon Sep 17 00:00:00 2001 From: john stultz Date: Mon, 26 Jun 2006 00:25:05 -0700 Subject: [PATCH] Time: Clocksource Infrastructure This introduces the clocksource management infrastructure. A clocksource is a driver-like architecture generic abstraction of a free-running counter. This code defines the clocksource structure, and provides management code for registering, selecting, accessing and scaling clocksources. Additionally, this includes the trivial jiffies clocksource, a lowest common denominator clocksource, provided mainly for use as an example. [hirofumi@mail.parknet.co.jp: Don't enable IRQ too early] Signed-off-by: John Stultz Signed-off-by: Ingo Molnar Signed-off-by: Paul Mundt Signed-off-by: John Stultz Signed-off-by: OGAWA Hirofumi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/clocksource.h | 181 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 181 insertions(+) create mode 100644 include/linux/clocksource.h (limited to 'include/linux/clocksource.h') diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h new file mode 100644 index 000000000000..c4187cda0ee4 --- /dev/null +++ b/include/linux/clocksource.h @@ -0,0 +1,181 @@ +/* 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 +#include +#include +#include +#include +#include + +/* 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. + * @interval_cycles: Used internally by timekeeping core, please ignore. + * @interval_snsecs: 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 interval_cycles; + u64 interval_snsecs; +}; + + +/** + * 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<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; +} + +/** + * calculate_clocksource_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 calculate_clocksource_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->interval_cycles = (cycle_t)tmp; + if(c->interval_cycles == 0) + c->interval_cycles = 1; + + c->interval_snsecs = (u64)c->interval_cycles * c->mult; +} + +/* used to install a new clocksource */ +int register_clocksource(struct clocksource*); +void reselect_clocksource(void); +struct clocksource* get_next_clocksource(void); + +#endif /* _LINUX_CLOCKSOURCE_H */ -- cgit v1.2.2