[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>

3 files changed, 418 insertions, 0 deletions

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);