Commit ad68b55a authored by FUJITA Tomonori's avatar FUJITA Tomonori Committed by Danilo Krummrich
Browse files

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: default avatarAndreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: default avatarAlice Ryhl <aliceryhl@google.com>
Signed-off-by: default avatarFUJITA Tomonori <fujita.tomonori@gmail.com>
Acked-by: default avatarAndreas Hindborg <a.hindborg@kernel.org>
Link: https://patch.msgid.link/20251103112958.2961517-2-fujita.tomonori@gmail.com


Signed-off-by: default avatarDanilo Krummrich <dakr@kernel.org>
parent fde40a55

rust/helpers/time.c

+5 −0
Original line number Diff line number Diff line
@@ -33,3 +33,8 @@ s64 rust_helper_ktime_to_ms(const ktime_t kt) 
{

	return ktime_to_ms(kt);

}



void rust_helper_udelay(unsigned long usec)

{

	udelay(usec);

}

rust/kernel/time/delay.rs

+37 −0
Original line number Diff line number Diff line
@@ -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)

    }

}