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linux-2.6/arch/x86/kernel/i8253.c

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/*
* 8253/PIT functions
*
*/
#include <linux/clockchips.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/timex.h>
#include <linux/delay.h>
#include <linux/i8253.h>
#include <linux/init.h>
#include <linux/io.h>
#include <asm/hpet.h>
#include <asm/smp.h>
/*
* HPET replaces the PIT, when enabled. So we need to know, which of
* the two timers is used
*/
struct clock_event_device *global_clock_event;
/*
* Initialize the PIT timer.
*
* This is also called after resume to bring the PIT into operation again.
*/
static void init_pit_timer(enum clock_event_mode mode,
struct clock_event_device *evt)
{
raw_spin_lock(&i8253_lock);
switch (mode) {
case CLOCK_EVT_MODE_PERIODIC:
/* binary, mode 2, LSB/MSB, ch 0 */
outb_pit(0x34, PIT_MODE);
outb_pit(LATCH & 0xff , PIT_CH0); /* LSB */
outb_pit(LATCH >> 8 , PIT_CH0); /* MSB */
break;
case CLOCK_EVT_MODE_SHUTDOWN:
case CLOCK_EVT_MODE_UNUSED:
if (evt->mode == CLOCK_EVT_MODE_PERIODIC ||
evt->mode == CLOCK_EVT_MODE_ONESHOT) {
outb_pit(0x30, PIT_MODE);
outb_pit(0, PIT_CH0);
outb_pit(0, PIT_CH0);
}
break;
case CLOCK_EVT_MODE_ONESHOT:
/* One shot setup */
outb_pit(0x38, PIT_MODE);
break;
case CLOCK_EVT_MODE_RESUME:
/* Nothing to do here */
break;
}
raw_spin_unlock(&i8253_lock);
}
/*
* Program the next event in oneshot mode
*
* Delta is given in PIT ticks
*/
static int pit_next_event(unsigned long delta, struct clock_event_device *evt)
{
raw_spin_lock(&i8253_lock);
outb_pit(delta & 0xff , PIT_CH0); /* LSB */
outb_pit(delta >> 8 , PIT_CH0); /* MSB */
raw_spin_unlock(&i8253_lock);
return 0;
}
/*
* On UP the PIT can serve all of the possible timer functions. On SMP systems
* it can be solely used for the global tick.
*
* The profiling and update capabilities are switched off once the local apic is
* registered. This mechanism replaces the previous #ifdef LOCAL_APIC -
* !using_apic_timer decisions in do_timer_interrupt_hook()
*/
static struct clock_event_device pit_ce = {
.name = "pit",
.features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
.set_mode = init_pit_timer,
.set_next_event = pit_next_event,
.irq = 0,
};
/*
* Initialize the conversion factor and the min/max deltas of the clock event
* structure and register the clock event source with the framework.
*/
void __init setup_pit_timer(void)
{
/*
* Start pit with the boot cpu mask and make it global after the
* IO_APIC has been initialized.
*/
pit_ce.cpumask = cpumask_of(smp_processor_id());
clockevents_config_and_register(&pit_ce, CLOCK_TICK_RATE, 0xF, 0x7FFF);
global_clock_event = &pit_ce;
}
#ifndef CONFIG_X86_64
static int __init init_pit_clocksource(void)
{
/*
* Several reasons not to register PIT as a clocksource:
*
* - On SMP PIT does not scale due to i8253_lock
* - when HPET is enabled
* - when local APIC timer is active (PIT is switched off)
*/
if (num_possible_cpus() > 1 || is_hpet_enabled() ||
pit_ce.mode != CLOCK_EVT_MODE_PERIODIC)
return 0;
return clocksource_i8253_init();
}
[PATCH] clocksource init adjustments (fix bug #7426) This patch resolves the issue found here: http://bugme.osdl.org/show_bug.cgi?id=7426 The basic summary is: Currently we register most of i386/x86_64 clocksources at module_init time. Then we enable clocksource selection at late_initcall time. This causes some problems for drivers that use gettimeofday for init calibration routines (specifically the es1968 driver in this case), where durring module_init, the only clocksource available is the low-res jiffies clocksource. This may cause slight calibration errors, due to the small sampling time used. It should be noted that drivers that require fine grained time may not function on architectures that do not have better then jiffies resolution timekeeping (there are a few). However, this does not discount the reasonable need for such fine-grained timekeeping at init time. Thus the solution here is to register clocksources earlier (ideally when the hardware is being initialized), and then we enable clocksource selection at fs_initcall (before device_initcall). This patch should probably get some testing time in -mm, since clocksource selection is one of the most important issues for correct timekeeping, and I've only been able to test this on a few of my own boxes. Signed-off-by: John Stultz <johnstul@us.ibm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@elte.hu> Cc: "David S. Miller" <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-03-05 08:30:50 +00:00
arch_initcall(init_pit_clocksource);
#endif /* !CONFIG_X86_64 */