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::{
49///     Io,
50///     Mmio,
51///     Region,
52///     poll::read_poll_timeout, //
53/// };
54/// use kernel::time::Delta;
55///
56/// const HW_READY: u16 = 0x01;
57///
58/// fn wait_for_hardware<const SIZE: usize>(io: Mmio<'_, Region<SIZE>>) -> Result {
59///     read_poll_timeout(
60///         // The `op` closure reads the value of a specific status register.
61///         || io.try_read16(0x1000),
62///         // The `cond` closure takes a reference to the value returned by `op`
63///         // and checks whether the hardware is ready.
64///         |val: &u16| *val == HW_READY,
65///         Delta::from_millis(50),
66///         Delta::from_secs(3),
67///     )?;
68///     Ok(())
69/// }
70/// ```
71#[track_caller]
72pub fn read_poll_timeout<Op, Cond, T>(
73    mut op: Op,
74    mut cond: Cond,
75    sleep_delta: Delta,
76    timeout_delta: Delta,
77) -> Result<T>
78where
79    Op: FnMut() -> Result<T>,
80    Cond: FnMut(&T) -> bool,
81{
82    let start: Instant<Monotonic> = Instant::now();
83
84    // Unlike the C version, we always call `might_sleep()` unconditionally,
85    // as conditional calls are error-prone. We clearly separate
86    // `read_poll_timeout()` and `read_poll_timeout_atomic()` to aid
87    // tools like klint.
88    might_sleep();
89
90    loop {
91        let val = op()?;
92        if cond(&val) {
93            // Unlike the C version, we immediately return.
94            // We know the condition is met so we don't need to check again.
95            return Ok(val);
96        }
97
98        if start.elapsed() > timeout_delta {
99            // Unlike the C version, we immediately return.
100            // We have just called `op()` so we don't need to call it again.
101            return Err(ETIMEDOUT);
102        }
103
104        if !sleep_delta.is_zero() {
105            fsleep(sleep_delta);
106        }
107
108        // `fsleep()` could be a busy-wait loop so we always call `cpu_relax()`.
109        cpu_relax();
110    }
111}
112
113/// Polls periodically until a condition is met, an error occurs,
114/// or the attempt limit is reached.
115///
116/// The function repeatedly executes the given operation `op` closure and
117/// checks its result using the condition closure `cond`.
118///
119/// If `cond` returns `true`, the function returns successfully with the result of `op`.
120/// Otherwise, it performs a busy wait for a duration specified by `delay_delta`
121/// before executing `op` again.
122///
123/// This process continues until either `op` returns an error, `cond`
124/// returns `true`, or the attempt limit specified by `retry` is reached.
125///
126/// # Errors
127///
128/// If `op` returns an error, then that error is returned directly.
129///
130/// If the attempt limit specified by `retry` is reached, then
131/// `Err(ETIMEDOUT)` is returned.
132///
133/// # Examples
134///
135/// ```no_run
136/// use kernel::io::{
137///     Io,
138///     Mmio,
139///     Region,
140///     poll::read_poll_timeout_atomic, //
141/// };
142/// use kernel::time::Delta;
143///
144/// const HW_READY: u16 = 0x01;
145///
146/// fn wait_for_hardware<const SIZE: usize>(io: Mmio<'_, Region<SIZE>>) -> Result {
147///     read_poll_timeout_atomic(
148///         // The `op` closure reads the value of a specific status register.
149///         || io.try_read16(0x1000),
150///         // The `cond` closure takes a reference to the value returned by `op`
151///         // and checks whether the hardware is ready.
152///         |val: &u16| *val == HW_READY,
153///         Delta::from_micros(50),
154///         1000,
155///     )?;
156///     Ok(())
157/// }
158/// ```
159pub fn read_poll_timeout_atomic<Op, Cond, T>(
160    mut op: Op,
161    mut cond: Cond,
162    delay_delta: Delta,
163    retry: usize,
164) -> Result<T>
165where
166    Op: FnMut() -> Result<T>,
167    Cond: FnMut(&T) -> bool,
168{
169    for _ in 0..retry {
170        let val = op()?;
171        if cond(&val) {
172            return Ok(val);
173        }
174
175        if !delay_delta.is_zero() {
176            udelay(delay_delta);
177        }
178
179        cpu_relax();
180    }
181
182    Err(ETIMEDOUT)
183}
kernel/io/poll.rs

kernel/io/
poll.rs
