rust: time: add Delta::as_millis_ceil()

Add a ceiling variant, mirroring the existing as_micros_ceil() since
the existing as_millis() truncates towards zero.

Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://patch.msgid.link/20260808062839.1159990-4-tomo@flapping.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
index 53b77abcb317..6c0a5e8090d0 100644
--- a/rust/kernel/time.rs
+++ b/rust/kernel/time.rs
@@ -528,6 +528,32 @@ impl Delta {
         }
     }
 
+    /// Return the smallest number of milliseconds greater than or equal
+    /// to the value in the [`Delta`].
+    #[inline]
+    pub fn as_millis_ceil(self) -> i64 {
+        // Only positive values need to be rounded up: truncating division already
+        // rounds towards zero, i.e. up, for negative values.
+        //
+        // The usual `(nanos + d - 1) / d` is not used because the addition overflows
+        // once `nanos` exceeds `i64::MAX - (d - 1)`; saturating the addition instead
+        // would drop the rounding bias and return a result one unit too small.
+        let n = self.as_nanos();
+
+        let (n, add) = if n > 0 { (n - 1, 1) } else { (n, 0) };
+
+        #[cfg(CONFIG_64BIT)]
+        {
+            n / NSEC_PER_MSEC + add
+        }
+
+        #[cfg(not(CONFIG_64BIT))]
+        // SAFETY: It is always safe to call `ktime_to_ms()` with any value.
+        unsafe {
+            bindings::ktime_to_ms(n) + add
+        }
+    }
+
     /// 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