Re: [PATCH v6 4/7] rust: time: add Delta::to_jiffies_timeout() for timeout conversion

On Sat Aug 8, 2026 at 7:28 AM BST, FUJITA Tomonori wrote:
> From: FUJITA Tomonori <[email protected]>
>
> Add Delta<Nsec>::to_jiffies_timeout() conversion that rounds up so the
> resulting timeout is never shorter than the requested span, clamps a
> negative span to an immediate timeout, and saturates an overlong span
> to the kernel's MAX_JIFFY_OFFSET "wait forever" value.
>
> Reviewed-by: Gary Guo <[email protected]>
> Signed-off-by: FUJITA Tomonori <[email protected]>
> ---
>  rust/kernel/time.rs | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> index af144d251f47..83891dab3aa7 100644
> --- a/rust/kernel/time.rs
> +++ b/rust/kernel/time.rs
> @@ -551,6 +551,27 @@ pub fn as_millis_ceil(self) -> i64 {
>          }
>      }
>  
> +    /// Convert this span to a [`Delta<Jiffy>`] suitable for use as a timeout.
> +    ///
> +    /// The value is rounded up to the next whole jiffy, so the resulting
> +    /// timeout is never shorter than `self` (as `msecs_to_jiffies()` does).
> +    /// A negative span clamps to zero jiffies (an immediate timeout).
> +    #[inline]
> +    pub fn to_jiffies_timeout(self) -> Delta<Jiffy> {
> +        let msecs = self.as_millis_ceil();
> +
> +        // CAST: `msecs` is clamped to `0..=c_uint::MAX`, so it is non-negative and
> +        // fits in `c_uint`.
> +        let msecs = msecs.clamp(0, i64::from(crate::ffi::c_uint::MAX)) as crate::ffi::c_uint;
> +
> +        // SAFETY: `__msecs_to_jiffies()` is always safe to call.
> +        let jiffies = unsafe { bindings::__msecs_to_jiffies(msecs) };
> +
> +        // CAST: `__msecs_to_jiffies()` returns a value in `0..=MAX_JIFFY_OFFSET`, i.e.
> +        // `((LONG_MAX >> 1) - 1)`, which is non-negative and well within `isize`.
> +        Delta::<Jiffy>::from_jiffies(jiffies as isize)
> +    }

I think it's fine to merge this as is, but I still want this to be simplified to
not have two divisions eventually.

Something like 

    fn to_jiffies(self) -> Delta<Jiffy> {
        // implement using nsecs_to_jiffies
    }

    fn to_jiffies_ceil(self) -> Delta<Jiffy> {
        // implement with to_jiffies
    }

    fn to_jiffies_timeout(self) -> Delta<Jiffy> {
        // implement with to_jiffies_timeout and clamp to 0
    }

Perhaps?

Best,
Gary


> +
>      /// Return `self % dividend` where `dividend` is in nanoseconds.
>      ///
>      /// The kernel doesn't have any emulation for `s64 % s64` on 32 bit platforms, so this is