[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>

5 files changed, 609 insertions, 4 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index bca6f389da66..968631678d4a 100644
--- a/Documentation/kernel-parameters.txt
+++ b/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).
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 */
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
new file mode 100644
index 000000000000..e1dfd8e86cce
--- /dev/null
+++ b/kernel/time/Makefile
@@ -0,0 +1 @@
+obj-y += clocksource.o jiffies.o
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
new file mode 100644
index 000000000000..95dd2200a109
--- /dev/null
+++ b/kernel/time/clocksource.c
@@ -0,0 +1,344 @@
+/*
+ * linux/kernel/time/clocksource.c
+ *
+ * This file contains the functions which manage clocksource drivers.
+ *
+ * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * TODO WishList:
+ *   o Allow clocksource drivers to be unregistered
+ *   o get rid of clocksource_jiffies extern
+ */
+
+#include <linux/clocksource.h>
+#include <linux/sysdev.h>
+#include <linux/init.h>
+#include <linux/module.h>
+
+/* XXX - Would like a better way for initializing curr_clocksource */
+extern struct clocksource clocksource_jiffies;
+
+/*[Clocksource internal variables]---------
+ * curr_clocksource:
+ *      currently selected clocksource. Initialized to clocksource_jiffies.
+ * next_clocksource:
+ *      pending next selected clocksource.
+ * clocksource_list:
+ *      linked list with the registered clocksources
+ * clocksource_lock:
+ *      protects manipulations to curr_clocksource and next_clocksource
+ *      and the clocksource_list
+ * override_name:
+ *      Name of the user-specified clocksource.
+ */
+static struct clocksource *curr_clocksource = &clocksource_jiffies;
+static struct clocksource *next_clocksource;
+static LIST_HEAD(clocksource_list);
+static DEFINE_SPINLOCK(clocksource_lock);
+static char override_name[32];
+static int finished_booting;
+
+/* clocksource_done_booting - Called near the end of bootup
+ *
+ * Hack to avoid lots of clocksource churn at boot time
+ */
+static int clocksource_done_booting(void)
+{
+        finished_booting = 1;
+        return 0;
+}
+
+late_initcall(clocksource_done_booting);
+
+/**
+ * get_next_clocksource - Returns the selected clocksource
+ *
+ */
+struct clocksource *get_next_clocksource(void)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&clocksource_lock, flags);
+        if (next_clocksource && finished_booting) {
+                curr_clocksource = next_clocksource;
+                next_clocksource = NULL;
+        }
+        spin_unlock_irqrestore(&clocksource_lock, flags);
+
+        return curr_clocksource;
+}
+
+/**
+ * select_clocksource - Finds the best registered clocksource.
+ *
+ * Private function. Must hold clocksource_lock when called.
+ *
+ * Looks through the list of registered clocksources, returning
+ * the one with the highest rating value. If there is a clocksource
+ * name that matches the override string, it returns that clocksource.
+ */
+static struct clocksource *select_clocksource(void)
+{
+        struct clocksource *best = NULL;
+        struct list_head *tmp;
+
+        list_for_each(tmp, &clocksource_list) {
+                struct clocksource *src;
+
+                src = list_entry(tmp, struct clocksource, list);
+                if (!best)
+                        best = src;
+
+                /* check for override: */
+                if (strlen(src->name) == strlen(override_name) &&
+                    !strcmp(src->name, override_name)) {
+                        best = src;
+                        break;
+                }
+                /* pick the highest rating: */
+                if (src->rating > best->rating)
+                        best = src;
+        }
+
+        return best;
+}
+
+/**
+ * is_registered_source - Checks if clocksource is registered
+ * @c:          pointer to a clocksource
+ *
+ * Private helper function. Must hold clocksource_lock when called.
+ *
+ * Returns one if the clocksource is already registered, zero otherwise.
+ */
+static int is_registered_source(struct clocksource *c)
+{
+        int len = strlen(c->name);
+        struct list_head *tmp;
+
+        list_for_each(tmp, &clocksource_list) {
+                struct clocksource *src;
+
+                src = list_entry(tmp, struct clocksource, list);
+                if (strlen(src->name) == len && !strcmp(src->name, c->name))
+                        return 1;
+        }
+
+        return 0;
+}
+
+/**
+ * register_clocksource - Used to install new clocksources
+ * @t:          clocksource to be registered
+ *
+ * Returns -EBUSY if registration fails, zero otherwise.
+ */
+int register_clocksource(struct clocksource *c)
+{
+        int ret = 0;
+        unsigned long flags;
+
+        spin_lock_irqsave(&clocksource_lock, flags);
+        /* check if clocksource is already registered */
+        if (is_registered_source(c)) {
+                printk("register_clocksource: Cannot register %s. "
+                        "Already registered!", c->name);
+                ret = -EBUSY;
+        } else {
+                /* register it */
+                list_add(&c->list, &clocksource_list);
+                /* scan the registered clocksources, and pick the best one */
+                next_clocksource = select_clocksource();
+        }
+        spin_unlock_irqrestore(&clocksource_lock, flags);
+        return ret;
+}
+
+EXPORT_SYMBOL(register_clocksource);
+
+/**
+ * reselect_clocksource - Rescan list for next clocksource
+ *
+ * A quick helper function to be used if a clocksource changes its
+ * rating. Forces the clocksource list to be re-scaned for the best
+ * clocksource.
+ */
+void reselect_clocksource(void)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&clocksource_lock, flags);
+        next_clocksource = select_clocksource();
+        spin_unlock_irqrestore(&clocksource_lock, flags);
+}
+
+/**
+ * sysfs_show_current_clocksources - sysfs interface for current clocksource
+ * @dev:        unused
+ * @buf:        char buffer to be filled with clocksource list
+ *
+ * Provides sysfs interface for listing current clocksource.
+ */
+static ssize_t
+sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
+{
+        char *curr = buf;
+
+        spin_lock_irq(&clocksource_lock);
+        curr += sprintf(curr, "%s ", curr_clocksource->name);
+        spin_unlock_irq(&clocksource_lock);
+
+        curr += sprintf(curr, "\n");
+
+        return curr - buf;
+}
+
+/**
+ * sysfs_override_clocksource - interface for manually overriding clocksource
+ * @dev:        unused
+ * @buf:        name of override clocksource
+ * @count:      length of buffer
+ *
+ * Takes input from sysfs interface for manually overriding the default
+ * clocksource selction.
+ */
+static ssize_t sysfs_override_clocksource(struct sys_device *dev,
+                                          const char *buf, size_t count)
+{
+        size_t ret = count;
+        /* strings from sysfs write are not 0 terminated! */
+        if (count >= sizeof(override_name))
+                return -EINVAL;
+
+        /* strip of \n: */
+        if (buf[count-1] == '\n')
+                count--;
+        if (count < 1)
+                return -EINVAL;
+
+        spin_lock_irq(&clocksource_lock);
+
+        /* copy the name given: */
+        memcpy(override_name, buf, count);
+        override_name[count] = 0;
+
+        /* try to select it: */
+        next_clocksource = select_clocksource();
+
+        spin_unlock_irq(&clocksource_lock);
+
+        return ret;
+}
+
+/**
+ * sysfs_show_available_clocksources - sysfs interface for listing clocksource
+ * @dev:        unused
+ * @buf:        char buffer to be filled with clocksource list
+ *
+ * Provides sysfs interface for listing registered clocksources
+ */
+static ssize_t
+sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
+{
+        struct list_head *tmp;
+        char *curr = buf;
+
+        spin_lock_irq(&clocksource_lock);
+        list_for_each(tmp, &clocksource_list) {
+                struct clocksource *src;
+
+                src = list_entry(tmp, struct clocksource, list);
+                curr += sprintf(curr, "%s ", src->name);
+        }
+        spin_unlock_irq(&clocksource_lock);
+
+        curr += sprintf(curr, "\n");
+
+        return curr - buf;
+}
+
+/*
+ * Sysfs setup bits:
+ */
+static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
+                        sysfs_override_clocksource);
+
+static SYSDEV_ATTR(available_clocksource, 0600,
+                        sysfs_show_available_clocksources, NULL);
+
+static struct sysdev_class clocksource_sysclass = {
+        set_kset_name("clocksource"),
+};
+
+static struct sys_device device_clocksource = {
+        .id     = 0,
+        .cls    = &clocksource_sysclass,
+};
+
+static int init_clocksource_sysfs(void)
+{
+        int error = sysdev_class_register(&clocksource_sysclass);
+
+        if (!error)
+                error = sysdev_register(&device_clocksource);
+        if (!error)
+                error = sysdev_create_file(
+                                &device_clocksource,
+                                &attr_current_clocksource);
+        if (!error)
+                error = sysdev_create_file(
+                                &device_clocksource,
+                                &attr_available_clocksource);
+        return error;
+}
+
+device_initcall(init_clocksource_sysfs);
+
+/**
+ * boot_override_clocksource - boot clock override
+ * @str:        override name
+ *
+ * Takes a clocksource= boot argument and uses it
+ * as the clocksource override name.
+ */
+static int __init boot_override_clocksource(char* str)
+{
+        unsigned long flags;
+        spin_lock_irqsave(&clocksource_lock, flags);
+        if (str)
+                strlcpy(override_name, str, sizeof(override_name));
+        spin_unlock_irqrestore(&clocksource_lock, flags);
+        return 1;
+}
+
+__setup("clocksource=", boot_override_clocksource);
+
+/**
+ * boot_override_clock - Compatibility layer for deprecated boot option
+ * @str:        override name
+ *
+ * DEPRECATED! Takes a clock= boot argument and uses it
+ * as the clocksource override name
+ */
+static int __init boot_override_clock(char* str)
+{
+        printk("Warning! clock= boot option is deprecated.\n");
+
+        return boot_override_clocksource(str);
+}
+
+__setup("clock=", boot_override_clock);
diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
new file mode 100644
index 000000000000..1fe8376e717b
--- /dev/null
+++ b/kernel/time/jiffies.c
@@ -0,0 +1,73 @@
+/***********************************************************************
+* linux/kernel/time/jiffies.c
+*
+* This file contains the jiffies based clocksource.
+*
+* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
+*
+* This program is free software; you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published by
+* the Free Software Foundation; either version 2 of the License, or
+* (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with this program; if not, write to the Free Software
+* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+*
+************************************************************************/
+#include <linux/clocksource.h>
+#include <linux/jiffies.h>
+#include <linux/init.h>
+
+/* The Jiffies based clocksource is the lowest common
+ * denominator clock source which should function on
+ * all systems. It has the same coarse resolution as
+ * the timer interrupt frequency HZ and it suffers
+ * inaccuracies caused by missed or lost timer
+ * interrupts and the inability for the timer
+ * interrupt hardware to accuratly tick at the
+ * requested HZ value. It is also not reccomended
+ * for "tick-less" systems.
+ */
+#define NSEC_PER_JIFFY  ((u32)((((u64)NSEC_PER_SEC)<<8)/ACTHZ))
+
+/* Since jiffies uses a simple NSEC_PER_JIFFY multiplier
+ * conversion, the .shift value could be zero. However
+ * this would make NTP adjustments impossible as they are
+ * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to
+ * shift both the nominator and denominator the same
+ * amount, and give ntp adjustments in units of 1/2^8
+ *
+ * The value 8 is somewhat carefully chosen, as anything
+ * larger can result in overflows. NSEC_PER_JIFFY grows as
+ * HZ shrinks, so values greater then 8 overflow 32bits when
+ * HZ=100.
+ */
+#define JIFFIES_SHIFT   8
+
+static cycle_t jiffies_read(void)
+{
+        return (cycle_t) jiffies;
+}
+
+struct clocksource clocksource_jiffies = {
+        .name           = "jiffies",
+        .rating         = 0, /* lowest rating*/
+        .read           = jiffies_read,
+        .mask           = 0xffffffff, /*32bits*/
+        .mult           = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
+        .shift          = JIFFIES_SHIFT,
+        .is_continuous  = 0, /* tick based, not free running */
+};
+
+static int __init init_jiffies_clocksource(void)
+{
+        return register_clocksource(&clocksource_jiffies);
+}
+
+module_init(init_jiffies_clocksource);