#ifndef _ASM_X86_TIMER_H
#define _ASM_X86_TIMER_H
#include <linux/init.h>
#include <linux/pm.h>
#include <linux/percpu.h>
#include <linux/interrupt.h>

#define TICK_SIZE (tick_nsec / 1000)

unsigned long long native_sched_clock(void);
extern int recalibrate_cpu_khz(void);

extern int no_timer_check;

/* Accelerators for sched_clock()
* 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_khz * 10^3))
* ns = cycles * (10^6 / cpu_khz)
*
* Then we use scaling math (suggested by [email protected]) to get:
* ns = cycles * (10^6 * SC / cpu_khz) / SC
* ns = cycles * cyc2ns_scale / SC
*
* And since SC is a constant power of two, we can convert the div
* into a shift.
*
* We can use khz divisor instead of mhz to keep a better precision, since
* cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
* ([email protected])
*
* [email protected] "math is hard, lets go shopping!"
*
* In:
*
* ns = cycles * cyc2ns_scale / SC
*
* Although we may still have enough bits to store the value of ns,
* in some cases, we may not have enough bits to store cycles * cyc2ns_scale,
* leading to an incorrect result.
*
* To avoid this, we can decompose 'cycles' into quotient and remainder
* of division by SC. Then,
*
* ns = (quot * SC + rem) * cyc2ns_scale / SC
* = quot * cyc2ns_scale + (rem * cyc2ns_scale) / SC
*
* - [email protected]
*/

DECLARE_PER_CPU(unsigned long, cyc2ns);
DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);

#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */

static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
{
int cpu = smp_processor_id();
unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
ns += mult_frac(cyc, per_cpu(cyc2ns, cpu),
(1UL << CYC2NS_SCALE_FACTOR));
return ns;
}

static inline unsigned long long cycles_2_ns(unsigned long long cyc)
{
unsigned long long ns;
unsigned long flags;

local_irq_save(flags);
ns = __cycles_2_ns(cyc);
local_irq_restore(flags);

return ns;
}

#endif /* _ASM_X86_TIMER_H */