/*
* 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);
