[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>

Documentation/kernel-parameters.txt

@@ -61,6 +61,7 @@ parameter is applicable:
 	MTD	MTD support is enabled.
 	NET	Appropriate network support is enabled.
 	NUMA	NUMA support is enabled.
+	GENERIC_TIME The generic timeofday code is enabled.
 	NFS	Appropriate NFS support is enabled.
 	OSS	OSS sound support is enabled.
 	PARIDE	The ParIDE subsystem is enabled.
@@ -341,10 +342,11 @@ running once the system is up.
 			Value can be changed at runtime via
 				/selinux/checkreqprot.
 
- 	clock=		[BUGS=IA-32,HW] gettimeofday timesource override.
-			Forces specified timesource (if avaliable) to be used
-			when calculating gettimeofday(). If specicified
-			timesource is not avalible, it defaults to PIT.
+	clock=		[BUGS=IA-32, HW] gettimeofday clocksource override.
+			[Deprecated]
+			Forces specified clocksource (if avaliable) to be used
+			when calculating gettimeofday(). If specified
+			clocksource is not avalible, it defaults to PIT.
 			Format: { pit | tsc | cyclone | pmtmr }
 
 	disable_8254_timer
@@ -1617,6 +1619,10 @@ running once the system is up.
 
 	time		Show timing data prefixed to each printk message line
 
+	clocksource=	[GENERIC_TIME] Override the default clocksource
+			Override the default clocksource and use the clocksource
+			with the name specified.
+
 	tipar.timeout=	[HW,PPT]
 			Set communications timeout in tenths of a second
 			(default 15).

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 */

kernel/time/Makefile

@@ -0,0 +1 @@
+obj-y += clocksource.o jiffies.o