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#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 0xFFFFFFFF
#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 = (cycle_t)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 (!hpet_address)
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);
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