kernel/io/
poll.rs

1// SPDX-License-Identifier: GPL-2.0
2
3//! IO polling.
4//!
5//! C header: [`include/linux/iopoll.h`](srctree/include/linux/iopoll.h).
6
7use crate::{
8    prelude::*,
9    processor::cpu_relax,
10    task::might_sleep,
11    time::{
12        delay::{
13            fsleep,
14            udelay, //
15        },
16        Delta,
17        Instant,
18        Monotonic, //
19    },
20};
21
22/// Polls periodically until a condition is met, an error occurs,
23/// or the timeout is reached.
24///
25/// The function repeatedly executes the given operation `op` closure and
26/// checks its result using the condition closure `cond`.
27///
28/// If `cond` returns `true`, the function returns successfully with
29/// the result of `op`. Otherwise, it waits for a duration specified
30/// by `sleep_delta` before executing `op` again.
31///
32/// This process continues until either `op` returns an error, `cond`
33/// returns `true`, or the timeout specified by `timeout_delta` is
34/// reached.
35///
36/// This function can only be used in a nonatomic context.
37///
38/// # Errors
39///
40/// If `op` returns an error, then that error is returned directly.
41///
42/// If the timeout specified by `timeout_delta` is reached, then
43/// `Err(ETIMEDOUT)` is returned.
44///
45/// # Examples
46///
47/// ```no_run
48/// use kernel::io::{Io, poll::read_poll_timeout};
49/// use kernel::time::Delta;
50///
51/// const HW_READY: u16 = 0x01;
52///
53/// fn wait_for_hardware<const SIZE: usize>(io: &Io<SIZE>) -> Result {
54///     read_poll_timeout(
55///         // The `op` closure reads the value of a specific status register.
56///         || io.try_read16(0x1000),
57///         // The `cond` closure takes a reference to the value returned by `op`
58///         // and checks whether the hardware is ready.
59///         |val: &u16| *val == HW_READY,
60///         Delta::from_millis(50),
61///         Delta::from_secs(3),
62///     )?;
63///     Ok(())
64/// }
65/// ```
66#[track_caller]
67pub fn read_poll_timeout<Op, Cond, T>(
68    mut op: Op,
69    mut cond: Cond,
70    sleep_delta: Delta,
71    timeout_delta: Delta,
72) -> Result<T>
73where
74    Op: FnMut() -> Result<T>,
75    Cond: FnMut(&T) -> bool,
76{
77    let start: Instant<Monotonic> = Instant::now();
78
79    // Unlike the C version, we always call `might_sleep()` unconditionally,
80    // as conditional calls are error-prone. We clearly separate
81    // `read_poll_timeout()` and `read_poll_timeout_atomic()` to aid
82    // tools like klint.
83    might_sleep();
84
85    loop {
86        let val = op()?;
87        if cond(&val) {
88            // Unlike the C version, we immediately return.
89            // We know the condition is met so we don't need to check again.
90            return Ok(val);
91        }
92
93        if start.elapsed() > timeout_delta {
94            // Unlike the C version, we immediately return.
95            // We have just called `op()` so we don't need to call it again.
96            return Err(ETIMEDOUT);
97        }
98
99        if !sleep_delta.is_zero() {
100            fsleep(sleep_delta);
101        }
102
103        // `fsleep()` could be a busy-wait loop so we always call `cpu_relax()`.
104        cpu_relax();
105    }
106}
107
108/// Polls periodically until a condition is met, an error occurs,
109/// or the attempt limit is reached.
110///
111/// The function repeatedly executes the given operation `op` closure and
112/// checks its result using the condition closure `cond`.
113///
114/// If `cond` returns `true`, the function returns successfully with the result of `op`.
115/// Otherwise, it performs a busy wait for a duration specified by `delay_delta`
116/// before executing `op` again.
117///
118/// This process continues until either `op` returns an error, `cond`
119/// returns `true`, or the attempt limit specified by `retry` is reached.
120///
121/// # Errors
122///
123/// If `op` returns an error, then that error is returned directly.
124///
125/// If the attempt limit specified by `retry` is reached, then
126/// `Err(ETIMEDOUT)` is returned.
127///
128/// # Examples
129///
130/// ```no_run
131/// use kernel::io::{poll::read_poll_timeout_atomic, Io};
132/// use kernel::time::Delta;
133///
134/// const HW_READY: u16 = 0x01;
135///
136/// fn wait_for_hardware<const SIZE: usize>(io: &Io<SIZE>) -> Result {
137///     read_poll_timeout_atomic(
138///         // The `op` closure reads the value of a specific status register.
139///         || io.try_read16(0x1000),
140///         // The `cond` closure takes a reference to the value returned by `op`
141///         // and checks whether the hardware is ready.
142///         |val: &u16| *val == HW_READY,
143///         Delta::from_micros(50),
144///         1000,
145///     )?;
146///     Ok(())
147/// }
148/// ```
149pub fn read_poll_timeout_atomic<Op, Cond, T>(
150    mut op: Op,
151    mut cond: Cond,
152    delay_delta: Delta,
153    retry: usize,
154) -> Result<T>
155where
156    Op: FnMut() -> Result<T>,
157    Cond: FnMut(&T) -> bool,
158{
159    for _ in 0..retry {
160        let val = op()?;
161        if cond(&val) {
162            return Ok(val);
163        }
164
165        if !delay_delta.is_zero() {
166            udelay(delay_delta);
167        }
168
169        cpu_relax();
170    }
171
172    Err(ETIMEDOUT)
173}
kernel/io/poll.rs

kernel/io/
poll.rs
