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(cycles: loops >> UDELAY_SHIFT); |
58 | } |
59 | |
60 | static void __timer_udelay(unsigned long usecs) |
61 | { |
62 | __timer_const_udelay(xloops: 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(mult: &new_mult, shift: &new_shift, from: timer->freq, |
71 | NSEC_PER_SEC, minsec: 3600); |
72 | res = cyc_to_ns(cyc: 1ULL, mult: new_mult, shift: 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 | |