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::prelude::*;
12
13/// Sleeps for a given duration at least.
14///
15/// Equivalent to the C side [`fsleep()`], flexible sleep function,
16/// which automatically chooses the best sleep method based on a duration.
17///
18/// `delta` must be within `[0, i32::MAX]` microseconds;
19/// otherwise, it is erroneous behavior. That is, it is considered a bug
20/// to call this function with an out-of-range value, in which case the function
21/// will sleep for at least the maximum value in the range and may warn
22/// in the future.
23///
24/// The behavior above differs from the C side [`fsleep()`] for which out-of-range
25/// values mean "infinite timeout" instead.
26///
27/// This function can only be used in a nonatomic context.
28///
29/// [`fsleep()`]: https://docs.kernel.org/timers/delay_sleep_functions.html#c.fsleep
30pub fn fsleep(delta: Delta) {
31    // The maximum value is set to `i32::MAX` microseconds to prevent integer
32    // overflow inside fsleep, which could lead to unintentional infinite sleep.
33    const MAX_DELTA: Delta = Delta::from_micros(i32::MAX as i64);
34
35    let delta = if (Delta::ZERO..=MAX_DELTA).contains(&delta) {
36        delta
37    } else {
38        // TODO: Add WARN_ONCE() when it's supported.
39        MAX_DELTA
40    };
41
42    // SAFETY: It is always safe to call `fsleep()` with any duration.
43    unsafe {
44        // Convert the duration to microseconds and round up to preserve
45        // the guarantee; `fsleep()` sleeps for at least the provided duration,
46        // but that it may sleep for longer under some circumstances.
47        bindings::fsleep(delta.as_micros_ceil() as c_ulong)
48    }
49}
50
51/// Inserts a delay based on microseconds with busy waiting.
52///
53/// Equivalent to the C side [`udelay()`], which delays in microseconds.
54///
55/// `delta` must be within `[0, MAX_UDELAY_MS]` in milliseconds;
56/// otherwise, it is erroneous behavior. That is, it is considered a bug to
57/// call this function with an out-of-range value.
58///
59/// The behavior above differs from the C side [`udelay()`] for which out-of-range
60/// values could lead to an overflow and unexpected behavior.
61///
62/// [`udelay()`]: https://docs.kernel.org/timers/delay_sleep_functions.html#c.udelay
63pub fn udelay(delta: Delta) {
64    const MAX_UDELAY_DELTA: Delta = Delta::from_millis(bindings::MAX_UDELAY_MS as i64);
65
66    debug_assert!(delta.as_nanos() >= 0);
67    debug_assert!(delta <= MAX_UDELAY_DELTA);
68
69    let delta = if (Delta::ZERO..=MAX_UDELAY_DELTA).contains(&delta) {
70        delta
71    } else {
72        MAX_UDELAY_DELTA
73    };
74
75    // SAFETY: It is always safe to call `udelay()` with any duration.
76    // Note that the kernel is compiled with `-fno-strict-overflow`
77    // so any out-of-range value could lead to unexpected behavior
78    // but won't lead to undefined behavior.
79    unsafe {
80        // Convert the duration to microseconds and round up to preserve
81        // the guarantee; `udelay()` inserts a delay for at least
82        // the provided duration, but that it may delay for longer
83        // under some circumstances.
84        bindings::udelay(delta.as_micros_ceil() as c_ulong)
85    }
86}