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clocksource: convert x86 to generic i8253 clocksource

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Convert x86 i8253 clocksource code to use generic i8253 clocksource.

Acked-by: John Stultz <john.stultz@linaro.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Russell King 2011-05-08 18:55:19 +01:00
parent 8c414ff3f4
commit 82491451dd
3 changed files with 4 additions and 78 deletions
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1
arch/x86/Kconfig
View File

@ -8,6 +8,7 @@ config 64BIT
config X86_32
def_bool !64BIT
select CLKSRC_I8253
config X86_64
def_bool 64BIT

2
arch/x86/include/asm/i8253.h
View File

@ -6,6 +6,8 @@
#define PIT_CH0 0x40
#define PIT_CH2 0x42
#define PIT_LATCH LATCH
extern raw_spinlock_t i8253_lock;
extern struct clock_event_device *global_clock_event;

79
arch/x86/kernel/i8253.c
View File

@ -117,81 +117,6 @@ void __init setup_pit_timer(void)
}
#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(struct clocksource *cs)
{
static int old_count;
static u32 old_jifs;
unsigned long flags;
int count;
u32 jifs;
raw_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;
raw_spin_unlock_irqrestore(&i8253_lock, flags);
count = (LATCH - 1) - count;
return (cycle_t)(jifs * LATCH) + count;
}
static struct clocksource pit_cs = {
.name = "pit",
.rating = 110,
.read = pit_read,
.mask = CLOCKSOURCE_MASK(32),
.mult = 0,
.shift = 20,
};
static int __init init_pit_clocksource(void)
{
/*
@ -205,9 +130,7 @@ static int __init init_pit_clocksource(void)
pit_ce.mode != CLOCK_EVT_MODE_PERIODIC)
return 0;
pit_cs.mult = clocksource_hz2mult(CLOCK_TICK_RATE, pit_cs.shift);
return clocksource_register(&pit_cs);
return clocksource_i8253_init();
}
arch_initcall(init_pit_clocksource);