[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 <johnstul@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 181 insertions, 0 deletions

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 <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.
+ * @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<<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;
+}
+
+/**
+ * read_clocksource: - 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 read_clocksource(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;
+}
+
+/**
+ * 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 */