[PATCH net-next v2 4/6] rust: time: add wrapper for fsleep function

[FUJITA Tomonori]

Add a wrapper for fsleep, flexible sleep functions in
`include/linux/delay.h` which deals with hardware delays.

The kernel supports several `sleep` functions to handle various
lengths of delay. This adds fsleep, automatically chooses the best
sleep method based on a duration.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxx>
---
 rust/helpers/time.c |  6 ++++++
 rust/kernel/time.rs | 16 ++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/rust/helpers/time.c b/rust/helpers/time.c
index 60dee69f4efc..0c85bb06af63 100644
--- a/rust/helpers/time.c
+++ b/rust/helpers/time.c
@@ -1,7 +1,13 @@
 // SPDX-License-Identifier: GPL-2.0
 
+#include <linux/delay.h>
 #include <linux/ktime.h>
 
+void rust_helper_fsleep(unsigned long usecs)
+{
+	fsleep(usecs);
+}
+
 ktime_t rust_helper_ktime_add_ns(const ktime_t kt, const u64 nsec)
 {
 	return ktime_add_ns(kt, nsec);
diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
index 3e00ad22ed89..5cca9c60f74a 100644
--- a/rust/kernel/time.rs
+++ b/rust/kernel/time.rs
@@ -5,9 +5,12 @@
 //! This module contains the kernel APIs related to time and timers that
 //! have been ported or wrapped for usage by Rust code in the kernel.
 //!
+//! C header: [`include/linux/delay.h`](srctree/include/linux/delay.h).
 //! C header: [`include/linux/jiffies.h`](srctree/include/linux/jiffies.h).
 //! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h).
 
+use core::ffi::c_ulong;
+
 /// The number of nanoseconds per microsecond.
 pub const NSEC_PER_USEC: i64 = bindings::NSEC_PER_USEC as i64;
 
@@ -178,3 +181,16 @@ fn add(self, delta: Delta) -> Ktime {
         Ktime::from_raw(t)
     }
 }
+
+/// Sleeps for a given duration.
+///
+/// Equivalent to the kernel's [`fsleep`], flexible sleep function,
+/// which automatically chooses the best sleep method based on a duration.
+///
+/// `Delta` must be longer than one microsecond.
+///
+/// This function can only be used in a nonatomic context.
+pub fn fsleep(delta: Delta) {
+    // SAFETY: FFI call.
+    unsafe { bindings::fsleep(delta.as_micros() as c_ulong) }
+}
-- 
2.34.1