linux-stable/arch/i386/kernel/hpet.c
john stultz 30f3174d1c [PATCH] Fix faulty HPET clocksource usage (fix for bug #7062)
Apparently some systems export valid HPET addresses, but hpet_enable()
fails.  Then when the HPET clocksource starts up, it only checks for a
valid HPET address, and the result is a system where time does not advance.

See http://bugme.osdl.org/show_bug.cgi?id=7062 for details.

This patch just makes sure we better check that the HPET is functional
before registering the HPET clocksource.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-09-01 11:39:08 -07:00

67 lines
1.5 KiB
C

#include <linux/clocksource.h>
#include <linux/errno.h>
#include <linux/hpet.h>
#include <linux/init.h>
#include <asm/hpet.h>
#include <asm/io.h>
#define HPET_MASK CLOCKSOURCE_MASK(32)
#define HPET_SHIFT 22
/* FSEC = 10^-15 NSEC = 10^-9 */
#define FSEC_PER_NSEC 1000000
static void *hpet_ptr;
static cycle_t read_hpet(void)
{
return (cycle_t)readl(hpet_ptr);
}
static struct clocksource clocksource_hpet = {
.name = "hpet",
.rating = 250,
.read = read_hpet,
.mask = HPET_MASK,
.mult = 0, /* set below */
.shift = HPET_SHIFT,
.is_continuous = 1,
};
static int __init init_hpet_clocksource(void)
{
unsigned long hpet_period;
void __iomem* hpet_base;
u64 tmp;
if (!is_hpet_enabled())
return -ENODEV;
/* calculate the hpet address: */
hpet_base =
(void __iomem*)ioremap_nocache(hpet_address, HPET_MMAP_SIZE);
hpet_ptr = hpet_base + HPET_COUNTER;
/* calculate the frequency: */
hpet_period = readl(hpet_base + HPET_PERIOD);
/*
* hpet period is in femto seconds per cycle
* so we need to convert this to ns/cyc units
* aproximated by mult/2^shift
*
* fsec/cyc * 1nsec/1000000fsec = nsec/cyc = mult/2^shift
* fsec/cyc * 1ns/1000000fsec * 2^shift = mult
* fsec/cyc * 2^shift * 1nsec/1000000fsec = mult
* (fsec/cyc << shift)/1000000 = mult
* (hpet_period << shift)/FSEC_PER_NSEC = mult
*/
tmp = (u64)hpet_period << HPET_SHIFT;
do_div(tmp, FSEC_PER_NSEC);
clocksource_hpet.mult = (u32)tmp;
return clocksource_register(&clocksource_hpet);
}
module_init(init_hpet_clocksource);