kernel/time/clocksource.c - maze/linux - Git at Google

 /*
  * 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 __init clocksource_done_booting(void)
 {
 	finished_booting = 1;
 	return 0;
 }

 late_initcall(clocksource_done_booting);

 /**
  * clocksource_get_next - Returns the selected clocksource
  *
  */
 struct clocksource *clocksource_get_next(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;
 }

 /**
  * clocksource_register - Used to install new clocksources
  * @t:		clocksource to be registered
  *
  * Returns -EBUSY if registration fails, zero otherwise.
  */
 int clocksource_register(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(clocksource_register);

 /**
  * clocksource_reselect - 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-scanned for the best
  * clocksource.
  */
 void clocksource_reselect(void)
 {
 	unsigned long flags;

 	spin_lock_irqsave(&clocksource_lock, flags);
 	next_clocksource = select_clocksource();
 	spin_unlock_irqrestore(&clocksource_lock, flags);
 }
 EXPORT_SYMBOL(clocksource_reselect);

 #ifdef CONFIG_SYSFS
 /**
  * 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 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);
 #endif /* CONFIG_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)
 {
 	if (!strcmp(str, "pmtmr")) {
 		printk("Warning: clock=pmtmr is deprecated. "
 			"Use clocksource=acpi_pm.\n");
 		return boot_override_clocksource("acpi_pm");
 	}
 	printk("Warning! clock= boot option is deprecated. "
 		"Use clocksource=xyz\n");
 	return boot_override_clocksource(str);
 }

 __setup("clock=", boot_override_clock);
	/*
	* 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 __init clocksource_done_booting(void)
	{
	finished_booting = 1;
	return 0;
	}

	late_initcall(clocksource_done_booting);

	/**
	* clocksource_get_next - Returns the selected clocksource
	*
	*/
	struct clocksource *clocksource_get_next(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;
	}

	/**
	* clocksource_register - Used to install new clocksources
	* @t: clocksource to be registered
	*
	* Returns -EBUSY if registration fails, zero otherwise.
	*/
	int clocksource_register(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(clocksource_register);

	/**
	* clocksource_reselect - 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-scanned for the best
	* clocksource.
	*/
	void clocksource_reselect(void)
	{
	unsigned long flags;

	spin_lock_irqsave(&clocksource_lock, flags);
	next_clocksource = select_clocksource();
	spin_unlock_irqrestore(&clocksource_lock, flags);
	}
	EXPORT_SYMBOL(clocksource_reselect);

	#ifdef CONFIG_SYSFS
	/**
	* 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 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);
	#endif /* CONFIG_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)
	{
	if (!strcmp(str, "pmtmr")) {
	printk("Warning: clock=pmtmr is deprecated. "
	"Use clocksource=acpi_pm.\n");
	return boot_override_clocksource("acpi_pm");
	}
	printk("Warning! clock= boot option is deprecated. "
	"Use clocksource=xyz\n");
	return boot_override_clocksource(str);
	}

	__setup("clock=", boot_override_clock);