[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>
This commit is contained in:
john stultz
committed by
Linus Torvalds
Linus Torvalds
parent
ade1a29e16
commit
734efb467b
1
kernel/time/Makefile
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1
kernel/time/Makefile
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@@ -0,0 +1 @@
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obj-y += clocksource.o jiffies.o
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344
kernel/time/clocksource.c
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344
kernel/time/clocksource.c
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@@ -0,0 +1,344 @@
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/*
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* linux/kernel/time/clocksource.c
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*
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* This file contains the functions which manage clocksource drivers.
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*
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* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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* TODO WishList:
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* o Allow clocksource drivers to be unregistered
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* o get rid of clocksource_jiffies extern
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*/
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#include <linux/clocksource.h>
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#include <linux/sysdev.h>
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#include <linux/init.h>
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#include <linux/module.h>
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/* XXX - Would like a better way for initializing curr_clocksource */
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extern struct clocksource clocksource_jiffies;
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/*[Clocksource internal variables]---------
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* curr_clocksource:
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* currently selected clocksource. Initialized to clocksource_jiffies.
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* next_clocksource:
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* pending next selected clocksource.
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* clocksource_list:
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* linked list with the registered clocksources
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* clocksource_lock:
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* protects manipulations to curr_clocksource and next_clocksource
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* and the clocksource_list
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* override_name:
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* Name of the user-specified clocksource.
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*/
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static struct clocksource *curr_clocksource = &clocksource_jiffies;
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static struct clocksource *next_clocksource;
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static LIST_HEAD(clocksource_list);
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static DEFINE_SPINLOCK(clocksource_lock);
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static char override_name[32];
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static int finished_booting;
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/* clocksource_done_booting - Called near the end of bootup
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*
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* Hack to avoid lots of clocksource churn at boot time
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*/
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static int clocksource_done_booting(void)
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{
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finished_booting = 1;
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return 0;
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}
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late_initcall(clocksource_done_booting);
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/**
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* get_next_clocksource - Returns the selected clocksource
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*
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*/
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struct clocksource *get_next_clocksource(void)
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{
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unsigned long flags;
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spin_lock_irqsave(&clocksource_lock, flags);
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if (next_clocksource && finished_booting) {
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curr_clocksource = next_clocksource;
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next_clocksource = NULL;
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}
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spin_unlock_irqrestore(&clocksource_lock, flags);
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return curr_clocksource;
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}
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/**
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* select_clocksource - Finds the best registered clocksource.
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*
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* Private function. Must hold clocksource_lock when called.
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*
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* Looks through the list of registered clocksources, returning
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* the one with the highest rating value. If there is a clocksource
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* name that matches the override string, it returns that clocksource.
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*/
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static struct clocksource *select_clocksource(void)
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{
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struct clocksource *best = NULL;
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struct list_head *tmp;
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list_for_each(tmp, &clocksource_list) {
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struct clocksource *src;
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src = list_entry(tmp, struct clocksource, list);
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if (!best)
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best = src;
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/* check for override: */
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if (strlen(src->name) == strlen(override_name) &&
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!strcmp(src->name, override_name)) {
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best = src;
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break;
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}
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/* pick the highest rating: */
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if (src->rating > best->rating)
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best = src;
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}
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return best;
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}
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/**
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* is_registered_source - Checks if clocksource is registered
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* @c: pointer to a clocksource
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*
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* Private helper function. Must hold clocksource_lock when called.
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*
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* Returns one if the clocksource is already registered, zero otherwise.
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*/
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static int is_registered_source(struct clocksource *c)
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{
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int len = strlen(c->name);
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struct list_head *tmp;
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list_for_each(tmp, &clocksource_list) {
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struct clocksource *src;
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src = list_entry(tmp, struct clocksource, list);
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if (strlen(src->name) == len && !strcmp(src->name, c->name))
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return 1;
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}
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return 0;
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}
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/**
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* register_clocksource - Used to install new clocksources
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* @t: clocksource to be registered
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*
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* Returns -EBUSY if registration fails, zero otherwise.
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*/
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int register_clocksource(struct clocksource *c)
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{
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int ret = 0;
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unsigned long flags;
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spin_lock_irqsave(&clocksource_lock, flags);
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/* check if clocksource is already registered */
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if (is_registered_source(c)) {
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printk("register_clocksource: Cannot register %s. "
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"Already registered!", c->name);
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ret = -EBUSY;
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} else {
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/* register it */
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list_add(&c->list, &clocksource_list);
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/* scan the registered clocksources, and pick the best one */
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next_clocksource = select_clocksource();
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}
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spin_unlock_irqrestore(&clocksource_lock, flags);
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return ret;
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}
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EXPORT_SYMBOL(register_clocksource);
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/**
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* reselect_clocksource - Rescan list for next clocksource
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*
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* A quick helper function to be used if a clocksource changes its
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* rating. Forces the clocksource list to be re-scaned for the best
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* clocksource.
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*/
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void reselect_clocksource(void)
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{
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unsigned long flags;
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spin_lock_irqsave(&clocksource_lock, flags);
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next_clocksource = select_clocksource();
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spin_unlock_irqrestore(&clocksource_lock, flags);
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}
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/**
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* sysfs_show_current_clocksources - sysfs interface for current clocksource
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* @dev: unused
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* @buf: char buffer to be filled with clocksource list
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*
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* Provides sysfs interface for listing current clocksource.
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*/
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static ssize_t
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sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
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{
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char *curr = buf;
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spin_lock_irq(&clocksource_lock);
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curr += sprintf(curr, "%s ", curr_clocksource->name);
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spin_unlock_irq(&clocksource_lock);
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curr += sprintf(curr, "\n");
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return curr - buf;
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}
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/**
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* sysfs_override_clocksource - interface for manually overriding clocksource
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* @dev: unused
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* @buf: name of override clocksource
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* @count: length of buffer
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*
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* Takes input from sysfs interface for manually overriding the default
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* clocksource selction.
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*/
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static ssize_t sysfs_override_clocksource(struct sys_device *dev,
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const char *buf, size_t count)
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{
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size_t ret = count;
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/* strings from sysfs write are not 0 terminated! */
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if (count >= sizeof(override_name))
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return -EINVAL;
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/* strip of \n: */
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if (buf[count-1] == '\n')
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count--;
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if (count < 1)
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return -EINVAL;
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spin_lock_irq(&clocksource_lock);
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/* copy the name given: */
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memcpy(override_name, buf, count);
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override_name[count] = 0;
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/* try to select it: */
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next_clocksource = select_clocksource();
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spin_unlock_irq(&clocksource_lock);
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return ret;
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}
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/**
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* sysfs_show_available_clocksources - sysfs interface for listing clocksource
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* @dev: unused
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* @buf: char buffer to be filled with clocksource list
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*
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* Provides sysfs interface for listing registered clocksources
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*/
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static ssize_t
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sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
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{
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struct list_head *tmp;
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char *curr = buf;
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spin_lock_irq(&clocksource_lock);
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list_for_each(tmp, &clocksource_list) {
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struct clocksource *src;
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src = list_entry(tmp, struct clocksource, list);
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curr += sprintf(curr, "%s ", src->name);
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}
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spin_unlock_irq(&clocksource_lock);
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curr += sprintf(curr, "\n");
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return curr - buf;
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}
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/*
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* Sysfs setup bits:
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*/
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static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
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sysfs_override_clocksource);
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static SYSDEV_ATTR(available_clocksource, 0600,
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sysfs_show_available_clocksources, NULL);
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static struct sysdev_class clocksource_sysclass = {
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set_kset_name("clocksource"),
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};
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static struct sys_device device_clocksource = {
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.id = 0,
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.cls = &clocksource_sysclass,
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};
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static int init_clocksource_sysfs(void)
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{
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int error = sysdev_class_register(&clocksource_sysclass);
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if (!error)
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error = sysdev_register(&device_clocksource);
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if (!error)
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error = sysdev_create_file(
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&device_clocksource,
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&attr_current_clocksource);
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if (!error)
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error = sysdev_create_file(
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&device_clocksource,
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&attr_available_clocksource);
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return error;
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}
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device_initcall(init_clocksource_sysfs);
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/**
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* boot_override_clocksource - boot clock override
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* @str: override name
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*
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* Takes a clocksource= boot argument and uses it
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* as the clocksource override name.
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*/
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static int __init boot_override_clocksource(char* str)
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{
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unsigned long flags;
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spin_lock_irqsave(&clocksource_lock, flags);
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if (str)
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strlcpy(override_name, str, sizeof(override_name));
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spin_unlock_irqrestore(&clocksource_lock, flags);
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return 1;
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}
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__setup("clocksource=", boot_override_clocksource);
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/**
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* boot_override_clock - Compatibility layer for deprecated boot option
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* @str: override name
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*
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* DEPRECATED! Takes a clock= boot argument and uses it
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* as the clocksource override name
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*/
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static int __init boot_override_clock(char* str)
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{
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printk("Warning! clock= boot option is deprecated.\n");
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return boot_override_clocksource(str);
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}
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__setup("clock=", boot_override_clock);
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73
kernel/time/jiffies.c
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73
kernel/time/jiffies.c
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@@ -0,0 +1,73 @@
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/***********************************************************************
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* linux/kernel/time/jiffies.c
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*
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* This file contains the jiffies based clocksource.
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*
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* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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************************************************************************/
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#include <linux/clocksource.h>
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#include <linux/jiffies.h>
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#include <linux/init.h>
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/* The Jiffies based clocksource is the lowest common
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* denominator clock source which should function on
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* all systems. It has the same coarse resolution as
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* the timer interrupt frequency HZ and it suffers
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* inaccuracies caused by missed or lost timer
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* interrupts and the inability for the timer
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* interrupt hardware to accuratly tick at the
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* requested HZ value. It is also not reccomended
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* for "tick-less" systems.
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*/
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#define NSEC_PER_JIFFY ((u32)((((u64)NSEC_PER_SEC)<<8)/ACTHZ))
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/* Since jiffies uses a simple NSEC_PER_JIFFY multiplier
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* conversion, the .shift value could be zero. However
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* this would make NTP adjustments impossible as they are
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* in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to
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* shift both the nominator and denominator the same
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* amount, and give ntp adjustments in units of 1/2^8
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*
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* The value 8 is somewhat carefully chosen, as anything
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* larger can result in overflows. NSEC_PER_JIFFY grows as
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* HZ shrinks, so values greater then 8 overflow 32bits when
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* HZ=100.
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*/
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#define JIFFIES_SHIFT 8
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static cycle_t jiffies_read(void)
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{
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return (cycle_t) jiffies;
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}
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struct clocksource clocksource_jiffies = {
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.name = "jiffies",
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.rating = 0, /* lowest rating*/
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.read = jiffies_read,
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.mask = 0xffffffff, /*32bits*/
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.mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
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.shift = JIFFIES_SHIFT,
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.is_continuous = 0, /* tick based, not free running */
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};
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static int __init init_jiffies_clocksource(void)
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{
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return register_clocksource(&clocksource_jiffies);
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}
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module_init(init_jiffies_clocksource);
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Reference in New Issue
Block a user