kernel/time/
delay.rs

1// SPDX-License-Identifier: GPL-2.0
2
3//! Delay and sleep primitives.
4//!
5//! This module contains the kernel APIs related to delay and sleep that
6//! have been ported or wrapped for usage by Rust code in the kernel.
7//!
8//! C header: [`include/linux/delay.h`](srctree/include/linux/delay.h).
9
10use super::Delta;
11use crate::{
12    pr_warn_once,
13    prelude::*, //
14};
15
16/// Sleeps for a given duration at least.
17///
18/// Equivalent to the C side [`fsleep()`], flexible sleep function,
19/// which automatically chooses the best sleep method based on a duration.
20///
21/// `delta` must be within `[0, i32::MAX]` microseconds;
22/// otherwise, it is erroneous behavior. That is, it is considered a bug
23/// to call this function with an out-of-range value, in which case the function
24/// will sleep for at least the maximum value in the range and warns once.
25///
26/// The behavior above differs from the C side [`fsleep()`] for which out-of-range
27/// values mean "infinite timeout" instead.
28///
29/// This function can only be used in a nonatomic context.
30///
31/// [`fsleep()`]: https://docs.kernel.org/timers/delay_sleep_functions.html#c.fsleep
32pub fn fsleep(delta: Delta) {
33    // The maximum value is set to `i32::MAX` microseconds to prevent integer
34    // overflow inside fsleep, which could lead to unintentional infinite sleep.
35    const MAX_DELTA: Delta = Delta::from_micros(i32::MAX as i64);
36
37    debug_assert!(delta.as_nanos() >= 0);
38    debug_assert!(delta <= MAX_DELTA);
39
40    let delta = if (Delta::ZERO..=MAX_DELTA).contains(&delta) {
41        delta
42    } else {
43        pr_warn_once!("attempted to fsleep() with out of range delta\n");
44        MAX_DELTA
45    };
46
47    // SAFETY: It is always safe to call `fsleep()` with any duration.
48    unsafe {
49        // Convert the duration to microseconds and round up to preserve
50        // the guarantee; `fsleep()` sleeps for at least the provided duration,
51        // but that it may sleep for longer under some circumstances.
52        bindings::fsleep(delta.as_micros_ceil() as c_ulong)
53    }
54}
55
56/// Inserts a delay based on microseconds with busy waiting.
57///
58/// Equivalent to the C side [`udelay()`], which delays in microseconds.
59///
60/// `delta` must be within `[0, MAX_UDELAY_MS]` in milliseconds;
61/// otherwise, it is erroneous behavior. That is, it is considered a bug to
62/// call this function with an out-of-range value, in which case the function
63/// will delay for at least the maximum value in the range and warns once.
64///
65/// The behavior above differs from the C side [`udelay()`] for which out-of-range
66/// values could lead to an overflow and unexpected behavior.
67///
68/// [`udelay()`]: https://docs.kernel.org/timers/delay_sleep_functions.html#c.udelay
69pub fn udelay(delta: Delta) {
70    const MAX_UDELAY_DELTA: Delta = Delta::from_millis(bindings::MAX_UDELAY_MS as i64);
71
72    debug_assert!(delta.as_nanos() >= 0);
73    debug_assert!(delta <= MAX_UDELAY_DELTA);
74
75    let delta = if (Delta::ZERO..=MAX_UDELAY_DELTA).contains(&delta) {
76        delta
77    } else {
78        pr_warn_once!("attempted to udelay() with out of range delta\n");
79        MAX_UDELAY_DELTA
80    };
81
82    // SAFETY: It is always safe to call `udelay()` with any duration.
83    // Note that the kernel is compiled with `-fno-strict-overflow`
84    // so any out-of-range value could lead to unexpected behavior
85    // but won't lead to undefined behavior.
86    unsafe {
87        // Convert the duration to microseconds and round up to preserve
88        // the guarantee; `udelay()` inserts a delay for at least
89        // the provided duration, but that it may delay for longer
90        // under some circumstances.
91        bindings::udelay(delta.as_micros_ceil() as c_ulong)
92    }
93}
kernel/time/delay.rs

kernel/time/
delay.rs
