From ad68b55a9ed0e5ce16508cb10081a73ea8f4bbef Mon Sep 17 00:00:00 2001 From: FUJITA Tomonori Date: Mon, 3 Nov 2025 20:29:57 +0900 Subject: rust: add udelay() function Add udelay() function, inserts a delay based on microseconds with busy waiting, in preparation for supporting read_poll_timeout_atomic(). Reviewed-by: Andreas Hindborg Reviewed-by: Alice Ryhl Signed-off-by: FUJITA Tomonori Acked-by: Andreas Hindborg Link: https://patch.msgid.link/20251103112958.2961517-2-fujita.tomonori@gmail.com Signed-off-by: Danilo Krummrich --- rust/kernel/time/delay.rs | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) (limited to 'rust/kernel/time/delay.rs') diff --git a/rust/kernel/time/delay.rs b/rust/kernel/time/delay.rs index eb8838da62bc..b5b1b42797a0 100644 --- a/rust/kernel/time/delay.rs +++ b/rust/kernel/time/delay.rs @@ -47,3 +47,40 @@ pub fn fsleep(delta: Delta) { bindings::fsleep(delta.as_micros_ceil() as c_ulong) } } + +/// Inserts a delay based on microseconds with busy waiting. +/// +/// Equivalent to the C side [`udelay()`], which delays in microseconds. +/// +/// `delta` must be within `[0, MAX_UDELAY_MS]` in milliseconds; +/// otherwise, it is erroneous behavior. That is, it is considered a bug to +/// call this function with an out-of-range value. +/// +/// The behavior above differs from the C side [`udelay()`] for which out-of-range +/// values could lead to an overflow and unexpected behavior. +/// +/// [`udelay()`]: https://docs.kernel.org/timers/delay_sleep_functions.html#c.udelay +pub fn udelay(delta: Delta) { + const MAX_UDELAY_DELTA: Delta = Delta::from_millis(bindings::MAX_UDELAY_MS as i64); + + debug_assert!(delta.as_nanos() >= 0); + debug_assert!(delta <= MAX_UDELAY_DELTA); + + let delta = if (Delta::ZERO..=MAX_UDELAY_DELTA).contains(&delta) { + delta + } else { + MAX_UDELAY_DELTA + }; + + // SAFETY: It is always safe to call `udelay()` with any duration. + // Note that the kernel is compiled with `-fno-strict-overflow` + // so any out-of-range value could lead to unexpected behavior + // but won't lead to undefined behavior. + unsafe { + // Convert the duration to microseconds and round up to preserve + // the guarantee; `udelay()` inserts a delay for at least + // the provided duration, but that it may delay for longer + // under some circumstances. + bindings::udelay(delta.as_micros_ceil() as c_ulong) + } +} -- cgit v1.2.3