1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Delay loops based on the OpenRISC implementation.
4  *
5  * Copyright (C) 2012 ARM Limited
6  *
7  * Author: Will Deacon <will.deacon@arm.com>
8  */
9 
10 #include <linux/clocksource.h>
11 #include <linux/delay.h>
12 #include <linux/init.h>
13 #include <linux/kernel.h>
14 #include <linux/module.h>
15 #include <linux/timex.h>
16 
17 /*
18  * Default to the loop-based delay implementation.
19  */
20 struct arm_delay_ops arm_delay_ops __ro_after_init = {
21 	.delay		= __loop_delay,
22 	.const_udelay	= __loop_const_udelay,
23 	.udelay		= __loop_udelay,
24 };
25 
26 static const struct delay_timer *delay_timer;
27 static bool delay_calibrated;
28 static u64 delay_res;
29 
read_current_timer(unsigned long * timer_val)30 int read_current_timer(unsigned long *timer_val)
31 {
32 	if (!delay_timer)
33 		return -ENXIO;
34 
35 	*timer_val = delay_timer->read_current_timer();
36 	return 0;
37 }
38 EXPORT_SYMBOL_GPL(read_current_timer);
39 
cyc_to_ns(u64 cyc,u32 mult,u32 shift)40 static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
41 {
42 	return (cyc * mult) >> shift;
43 }
44 
__timer_delay(unsigned long cycles)45 static void __timer_delay(unsigned long cycles)
46 {
47 	cycles_t start = get_cycles();
48 
49 	while ((get_cycles() - start) < cycles)
50 		cpu_relax();
51 }
52 
__timer_const_udelay(unsigned long xloops)53 static void __timer_const_udelay(unsigned long xloops)
54 {
55 	unsigned long long loops = xloops;
56 	loops *= arm_delay_ops.ticks_per_jiffy;
57 	__timer_delay(loops >> UDELAY_SHIFT);
58 }
59 
__timer_udelay(unsigned long usecs)60 static void __timer_udelay(unsigned long usecs)
61 {
62 	__timer_const_udelay(usecs * UDELAY_MULT);
63 }
64 
register_current_timer_delay(const struct delay_timer * timer)65 void __init register_current_timer_delay(const struct delay_timer *timer)
66 {
67 	u32 new_mult, new_shift;
68 	u64 res;
69 
70 	clocks_calc_mult_shift(&new_mult, &new_shift, timer->freq,
71 			       NSEC_PER_SEC, 3600);
72 	res = cyc_to_ns(1ULL, new_mult, new_shift);
73 
74 	if (res > 1000) {
75 		pr_err("Ignoring delay timer %ps, which has insufficient resolution of %lluns\n",
76 			timer, res);
77 		return;
78 	}
79 
80 	if (!delay_calibrated && (!delay_res || (res < delay_res))) {
81 		pr_info("Switching to timer-based delay loop, resolution %lluns\n", res);
82 		delay_timer			= timer;
83 		lpj_fine			= timer->freq / HZ;
84 		delay_res			= res;
85 
86 		/* cpufreq may scale loops_per_jiffy, so keep a private copy */
87 		arm_delay_ops.ticks_per_jiffy	= lpj_fine;
88 		arm_delay_ops.delay		= __timer_delay;
89 		arm_delay_ops.const_udelay	= __timer_const_udelay;
90 		arm_delay_ops.udelay		= __timer_udelay;
91 	} else {
92 		pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
93 	}
94 }
95 
calibrate_delay_is_known(void)96 unsigned long calibrate_delay_is_known(void)
97 {
98 	delay_calibrated = true;
99 	return lpj_fine;
100 }
101 
calibration_delay_done(void)102 void calibration_delay_done(void)
103 {
104 	delay_calibrated = true;
105 }
106