linux/arch/x86/kernel/i8253.c

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/*
* 8253/PIT functions
*
*/
#include <linux/clockchips.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <asm/smp.h>
#include <asm/delay.h>
#include <asm/i8253.h>
#include <asm/io.h>
#include <asm/hpet.h>
DEFINE_SPINLOCK(i8253_lock);
EXPORT_SYMBOL(i8253_lock);
#ifdef CONFIG_X86_32
static void pit_disable_clocksource(void);
#else
static inline void pit_disable_clocksource(void) { }
#endif
/*
* 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)
{
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);
}
pit_disable_clocksource();
break;
case CLOCK_EVT_MODE_ONESHOT:
/* One shot setup */
pit_disable_clocksource();
outb_pit(0x38, PIT_MODE);
break;
case CLOCK_EVT_MODE_RESUME:
/* Nothing to do here */
break;
}
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)
{
spin_lock(&i8253_lock);
outb_pit(delta & 0xff , PIT_CH0); /* LSB */
outb_pit(delta >> 8 , PIT_CH0); /* MSB */
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_clockevent = {
.name = "pit",
.features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
.set_mode = init_pit_timer,
.set_next_event = pit_next_event,
.shift = 32,
.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_clockevent.cpumask = cpumask_of(smp_processor_id());
pit_clockevent.mult = div_sc(CLOCK_TICK_RATE, NSEC_PER_SEC,
pit_clockevent.shift);
pit_clockevent.max_delta_ns =
clockevent_delta2ns(0x7FFF, &pit_clockevent);
pit_clockevent.min_delta_ns =
clockevent_delta2ns(0xF, &pit_clockevent);
clockevents_register_device(&pit_clockevent);
global_clock_event = &pit_clockevent;
}
#ifndef CONFIG_X86_64
/*
* Since the PIT overflows every tick, its not very useful
* to just read by itself. So use jiffies to emulate a free
* running counter:
*/
static cycle_t pit_read(void)
{
unsigned long flags;
int count;
u32 jifs;
static int old_count;
static u32 old_jifs;
spin_lock_irqsave(&i8253_lock, flags);
/*
* Although our caller may have the read side of xtime_lock,
* this is now a seqlock, and we are cheating in this routine
* by having side effects on state that we cannot undo if
* there is a collision on the seqlock and our caller has to
* retry. (Namely, old_jifs and old_count.) So we must treat
* jiffies as volatile despite the lock. We read jiffies
* before latching the timer count to guarantee that although
* the jiffies value might be older than the count (that is,
* the counter may underflow between the last point where
* jiffies was incremented and the point where we latch the
* count), it cannot be newer.
*/
jifs = jiffies;
outb_pit(0x00, PIT_MODE); /* latch the count ASAP */
count = inb_pit(PIT_CH0); /* read the latched count */
count |= inb_pit(PIT_CH0) << 8;
/* VIA686a test code... reset the latch if count > max + 1 */
if (count > LATCH) {
outb_pit(0x34, PIT_MODE);
outb_pit(LATCH & 0xff, PIT_CH0);
outb_pit(LATCH >> 8, PIT_CH0);
count = LATCH - 1;
}
/*
* It's possible for count to appear to go the wrong way for a
* couple of reasons:
*
* 1. The timer counter underflows, but we haven't handled the
* resulting interrupt and incremented jiffies yet.
* 2. Hardware problem with the timer, not giving us continuous time,
* the counter does small "jumps" upwards on some Pentium systems,
* (see c't 95/10 page 335 for Neptun bug.)
*
* Previous attempts to handle these cases intelligently were
* buggy, so we just do the simple thing now.
*/
if (count > old_count && jifs == old_jifs) {
count = old_count;
}
old_count = count;
old_jifs = jifs;
spin_unlock_irqrestore(&i8253_lock, flags);
count = (LATCH - 1) - count;
return (cycle_t)(jifs * LATCH) + count;
}
static struct clocksource clocksource_pit = {
.name = "pit",
.rating = 110,
.read = pit_read,
.mask = CLOCKSOURCE_MASK(32),
.mult = 0,
.shift = 20,
};
static void pit_disable_clocksource(void)
{
/*
* Use mult to check whether it is registered or not
*/
if (clocksource_pit.mult) {
clocksource_unregister(&clocksource_pit);
clocksource_pit.mult = 0;
}
}
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_clockevent.mode != CLOCK_EVT_MODE_PERIODIC)
return 0;
clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE,
clocksource_pit.shift);
return clocksource_register(&clocksource_pit);
}
[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