1/* SPDX-License-Identifier: GPL-2.0 */
 2#ifndef _ASM_X86_TIMER_H
 3#define _ASM_X86_TIMER_H
 
 4#include <linux/pm.h>
 5#include <linux/percpu.h>
 6#include <linux/interrupt.h>
 7#include <linux/math64.h>
 8
 9#define TICK_SIZE (tick_nsec / 1000)
10
11unsigned long long native_sched_clock(void);
12extern void recalibrate_cpu_khz(void);
13
14extern int no_timer_check;
15
16extern bool using_native_sched_clock(void);
17
18/*
19 * We use the full linear equation: f(x) = a + b*x, in order to allow
20 * a continuous function in the face of dynamic freq changes.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
21 *
22 * Continuity means that when our frequency changes our slope (b); we want to
23 * ensure that: f(t) == f'(t), which gives: a + b*t == a' + b'*t.
24 *
25 * Without an offset (a) the above would not be possible.
 
 
26 *
27 * See the comment near cycles_2_ns() for details on how we compute (b).
 
 
 
 
 
 
28 */
29struct cyc2ns_data {
30	u32 cyc2ns_mul;
31	u32 cyc2ns_shift;
32	u64 cyc2ns_offset;
33}; /* 16 bytes */
34
35extern void cyc2ns_read_begin(struct cyc2ns_data *);
36extern void cyc2ns_read_end(void);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
37
38#endif /* _ASM_X86_TIMER_H */

 
 1#ifndef _ASM_X86_TIMER_H
 2#define _ASM_X86_TIMER_H
 3#include <linux/init.h>
 4#include <linux/pm.h>
 5#include <linux/percpu.h>
 6#include <linux/interrupt.h>
 
 7
 8#define TICK_SIZE (tick_nsec / 1000)
 9
10unsigned long long native_sched_clock(void);
11extern int recalibrate_cpu_khz(void);
12
13extern int no_timer_check;
14
15/* Accelerators for sched_clock()
16 * convert from cycles(64bits) => nanoseconds (64bits)
17 *  basic equation:
18 *		ns = cycles / (freq / ns_per_sec)
19 *		ns = cycles * (ns_per_sec / freq)
20 *		ns = cycles * (10^9 / (cpu_khz * 10^3))
21 *		ns = cycles * (10^6 / cpu_khz)
22 *
23 *	Then we use scaling math (suggested by george@mvista.com) to get:
24 *		ns = cycles * (10^6 * SC / cpu_khz) / SC
25 *		ns = cycles * cyc2ns_scale / SC
26 *
27 *	And since SC is a constant power of two, we can convert the div
28 *  into a shift.
29 *
30 *  We can use khz divisor instead of mhz to keep a better precision, since
31 *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
32 *  (mathieu.desnoyers@polymtl.ca)
33 *
34 *			-johnstul@us.ibm.com "math is hard, lets go shopping!"
35 *
36 * In:
37 *
38 * ns = cycles * cyc2ns_scale / SC
 
39 *
40 * Although we may still have enough bits to store the value of ns,
41 * in some cases, we may not have enough bits to store cycles * cyc2ns_scale,
42 * leading to an incorrect result.
43 *
44 * To avoid this, we can decompose 'cycles' into quotient and remainder
45 * of division by SC.  Then,
46 *
47 * ns = (quot * SC + rem) * cyc2ns_scale / SC
48 *    = quot * cyc2ns_scale + (rem * cyc2ns_scale) / SC
49 *
50 *			- sqazi@google.com
51 */
 
 
 
 
 
52
53DECLARE_PER_CPU(unsigned long, cyc2ns);
54DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);
55
56#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
57
58static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
59{
60	int cpu = smp_processor_id();
61	unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
62	ns += mult_frac(cyc, per_cpu(cyc2ns, cpu),
63			(1UL << CYC2NS_SCALE_FACTOR));
64	return ns;
65}
66
67static inline unsigned long long cycles_2_ns(unsigned long long cyc)
68{
69	unsigned long long ns;
70	unsigned long flags;
71
72	local_irq_save(flags);
73	ns = __cycles_2_ns(cyc);
74	local_irq_restore(flags);
75
76	return ns;
77}
78
79#endif /* _ASM_X86_TIMER_H */