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
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
40 static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
41 {
42 return (cyc * mult) >> shift;
43 }
44
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
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
60 static void __timer_udelay(unsigned long usecs)
61 {
62 __timer_const_udelay(usecs * UDELAY_MULT);
63 }
64
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
96 unsigned long calibrate_delay_is_known(void)
97 {
98 delay_calibrated = true;
99 return lpj_fine;
100 }
101
102 void calibration_delay_done(void)
103 {
104 delay_calibrated = true;
105 }
106
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