/*
* This code largely moved from arch/i386/kernel/time.c.
* See comments there for proper credits.
*/
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/timex.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/jiffies.h>
#include <asm/timer.h>
#include <asm/io.h>
#include <asm/processor.h>
#include "io_ports.h"
#include "mach_timer.h"
#include <asm/hpet.h>
static unsigned long hpet_usec_quotient; /* convert hpet clks to usec */
static unsigned long tsc_hpet_quotient; /* convert tsc to hpet clks */
static unsigned long hpet_last; /* hpet counter value at last tick*/
static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */
static unsigned long last_tsc_high; /* msb 32 bits of Time Stamp Counter */
static unsigned long long monotonic_base;
static seqlock_t monotonic_lock = SEQLOCK_UNLOCKED;
/* convert from cycles(64bits) => nanoseconds (64bits)
* basic equation:
* ns = cycles / (freq / ns_per_sec)
* ns = cycles * (ns_per_sec / freq)
* ns = cycles * (10^9 / (cpu_mhz * 10^6))
* ns = cycles * (10^3 / cpu_mhz)
*
* Then we use scaling math (suggested by george@mvista.com) to get:
* ns = cycles * (10^3 * SC / cpu_mhz) / SC
* ns = cycles * cyc2ns_scale / SC
*
* And since SC is a constant power of two, we can convert the div
* into a shift.
* -johnstul@us.ibm.com "math is hard, lets go shopping!"
*/
static unsigned long cyc2ns_scale;
#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
static inline void set_cyc2ns_scale(unsigned long cpu_mhz)
{
cyc2ns_scale = (1000 << CYC2NS_SCALE_FACTOR)/cpu_mhz;
}
static inline unsigned long long cycles_2_ns(unsigned long long cyc)
{
return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
}
static unsigned long long monotonic_clock_hpet(void)
{
unsigned long long last_offset, this_offset, base;
unsigned seq;
/* atomically read monotonic base & last_offset */
do {
seq = read_seqbegin(&monotonic_lock);
last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
base = monotonic_base;
} while (read_seqretry(&monotonic_lock, seq));
/* Read the Time Stamp Counter */
rdtscll(this_offset);
/* return the value in ns */
return base + cycles_2_ns(this_offset - last_offset);
}
static unsigned long get_offset_hpet(void)
{
register unsigned long eax, edx;
eax = hpet_readl(HPET_COUNTER);
eax -= hpet_last; /* hpet delta */
eax = min(hpet_tick, eax);
/*
* Time offset = (hpet delta) * ( usecs per HPET clock )
* = (hpet delta) * ( usecs per tick / HPET clocks per tick)
* = (hpet delta) * ( hpet_usec_quotient ) / (2^32)
*
* Where,
* hpet_usec_quotient = (2^32 * usecs per tick)/HPET clocks per tick
*
* Using a mull instead of a divl saves some cycles in critical path.
*/
ASM_MUL64_REG(eax, edx, hpet_usec_quotient, eax);
/* our adjusted time offset in microseconds */
return edx;
}
static void mark_offset_hpet(void)
{
unsigned long long this_offset, last_offset;
unsigned long offset;
write_seqlock(&monotonic_lock);
last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
rdtsc(last_tsc_low, last_tsc_high);
if (hpet_use_timer)
offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
else
offset = hpet_readl(HPET_COUNTER);
if (unlikely(((offset - hpet_last) >= (2*hpet_tick)) && (hpet_last != 0))) {
int lost_ticks = ((offset - hpet_last) / hpet_tick) - 1;
jiffies_64 += lost_ticks;
}
hpet_last = offset;
/* update the monotonic base value */
this_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
monotonic_base += cycles_2_ns(this_offset - last_offset);
write_sequnlock(&monotonic_lock);
}
static void delay_hpet(unsigned long loops)
{
unsigned long hpet_start, hpet_end;
unsigned long eax;
/* loops is the number of cpu cycles. Convert it to hpet clocks */
ASM_MUL64_REG(eax, loops, tsc_hpet_quotient, loops);
hpet_start = hpet_readl(HPET_COUNTER);
do {
rep_nop();
hpet_end = hpet_readl(HPET_COUNTER);
} while ((hpet_end - hpet_start) < (loops));
}
static int __init init_hpet(char* override)
{
unsigned long result, remain;
/* check clock override */
if (override[0] && strncmp(override,"hpet",4))
return -ENODEV;
if (!is_hpet_enabled())
return -ENODEV;
printk("Using HPET for gettimeofday\n");
if (cpu_has_tsc) {
unsigned long tsc_quotient = calibrate_tsc_hpet(&tsc_hpet_quotient);
if (tsc_quotient) {
/* report CPU clock rate in Hz.
* The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
* clock/second. Our precision is about 100 ppm.
*/
{ unsigned long eax=0, edx=1000;
ASM_DIV64_REG(cpu_khz, edx, tsc_quotient,
eax, edx);
printk("Detected %lu.%03lu MHz processor.\n",
cpu_khz / 1000, cpu_khz % 1000);
}
set_cyc2ns_scale(cpu_khz/1000);
}
}
/*
* Math to calculate hpet to usec multiplier
* Look for the comments at get_offset_hpet()
*/
ASM_DIV64_REG(result, remain, hpet_tick, 0, KERNEL_TICK_USEC);
if (remain > (hpet_tick >> 1))
result++; /* rounding the result */
hpet_usec_quotient = result;
return 0;
}
/************************************************************/
/* tsc timer_opts struct */
static struct timer_opts timer_hpet = {
.name = "hpet",
.mark_offset = mark_offset_hpet,
.get_offset = get_offset_hpet,
.monotonic_clock = monotonic_clock_hpet,
.delay = delay_hpet,
};
struct init_timer_opts __initdata timer_hpet_init = {
.init = init_hpet,
.opts = &timer_hpet,
};
