[PATCH v4 5/7] rust: workqueue: take a Delta<Jiffy> for the enqueue delay

[FUJITA Tomonori <tomo@flapping.org>]

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

enqueue_delayed() takes the delay as a raw Jiffies (c_ulong). That is
the C representation rather than a kernel time type, so it neither
carries the unit in its type nor composes with the Delta arithmetic
used elsewhere for expressing spans, and it forces callers to hand the
API a bare integer.

Change the delay parameter to Delta<Jiffy> so a delay is expressed in
the same time vocabulary as the rest of the kernel crate. A signed
Delta can be negative, so clamp it to zero before handing it to the C
side, which keeps "no delay" the natural meaning of a non-positive
span.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
---
 rust/kernel/workqueue.rs | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index 7e253b6f299c..d4f8a3ea5acb 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -171,7 +171,7 @@
 //! /// This method will enqueue the struct for execution on the system workqueue, where its value
 //! /// will be printed 12 jiffies later.
 //! fn print_later(val: Arc<MyStruct>) {
-//!     let _ = workqueue::system().enqueue_delayed(val, 12);
+//!     let _ = workqueue::system().enqueue_delayed(val, kernel::time::Delta::from_jiffies(12));
 //! }
 //!
 //! /// It is also possible to use the ordinary `enqueue` method together with `DelayedWork`. This
@@ -197,7 +197,10 @@
         Arc,
         LockClassKey, //
     },
-    time::Jiffies,
+    time::{
+        Delta,
+        Jiffy, //
+    },
     types::Opaque,
 };
 use core::{marker::PhantomData, ptr::NonNull};
@@ -303,11 +306,14 @@ pub fn enqueue<W, const ID: u64>(&self, w: W) -> W::EnqueueOutput
     /// This may fail if the work item is already enqueued in a workqueue.
     ///
     /// The work item will be submitted using `WORK_CPU_UNBOUND`.
-    pub fn enqueue_delayed<W, const ID: u64>(&self, w: W, delay: Jiffies) -> W::EnqueueOutput
+    pub fn enqueue_delayed<W, const ID: u64>(&self, w: W, delta: Delta<Jiffy>) -> W::EnqueueOutput
     where
         W: RawDelayedWorkItem<ID> + Send + 'static,
     {
         let queue_ptr = self.0.get();
+        // CAST: A negative delay is clamped to `0`, so the value is non-negative
+        // and fits in `c_ulong`.
+        let delay = delta.as_jiffies().max(0) as ffi::c_ulong;
 
         // SAFETY: We only return `false` if the `work_struct` is already in a workqueue. The other
         // `__enqueue` requirements are not relevant since `W` is `Send` and static.
-- 
2.43.0