[PATCH v8 1/4] rust: time: make Delta::ZERO generic over the time unit

[FUJITA Tomonori <tomo@flapping.org>]

From: FUJITA Tomonori <fujita.tomonori@gmail.com>

Delta::ZERO is defined only for Delta<Nsec>, so code that needs a zero
Delta<Jiffy> has to write Delta::from_jiffies(0).

Define ZERO for every Delta<U> instead. An integer literal cannot be
used for a generic U::Repr, so add ZERO to TimeUnit.

Suggested-by: Markus Probst <markus.probst@posteo.de>
Suggested-by: Gary Guo <gary@garyguo.net>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
---
 rust/kernel/time.rs | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
index 5ae377e70dd8..9f231bf25ead 100644
--- a/rust/kernel/time.rs
+++ b/rust/kernel/time.rs
@@ -306,6 +306,9 @@ impl Sealed for super::Jiffy {}
 pub trait TimeUnit: private::Sealed {
     /// The underlying representation of the time unit.
     type Repr: Copy + Clone + PartialEq + PartialOrd + Eq + Ord + core::fmt::Debug;
+
+    /// The zero value of [`Self::Repr`].
+    const ZERO: Self::Repr;
 }
 
 /// A time unit of nanoseconds.
@@ -317,6 +320,7 @@ pub enum Nsec {}
 
 impl TimeUnit for Nsec {
     type Repr = i64;
+    const ZERO: Self::Repr = 0;
 }
 
 /// A time unit of jiffies.
@@ -328,6 +332,7 @@ pub enum Jiffy {}
 
 impl TimeUnit for Jiffy {
     type Repr = isize;
+    const ZERO: Self::Repr = 0;
 }
 
 /// A span of time.
@@ -341,6 +346,11 @@ pub struct Delta<U: TimeUnit = Nsec> {
     value: U::Repr,
 }
 
+impl<U: TimeUnit> Delta<U> {
+    /// A span of time equal to zero.
+    pub const ZERO: Self = Self { value: U::ZERO };
+}
+
 impl Delta<Jiffy> {
     /// Create a new [`Delta`] from a number of jiffies.
     #[inline]
@@ -428,9 +438,6 @@ fn div(self, rhs: Self) -> Self::Output {
 }
 
 impl Delta {
-    /// A span of time equal to zero.
-    pub const ZERO: Self = Self { value: 0 };
-
     /// Create a new [`Delta`] from a number of nanoseconds.
     #[inline]
     pub const fn from_nanos(nanos: i64) -> Self {
-- 
2.43.0