Commit 1b7bbd59 authored by FUJITA Tomonori's avatar FUJITA Tomonori Committed by Andreas Hindborg
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rust: time: Avoid 64-bit integer division on 32-bit architectures 



Avoid 64-bit integer division that 32-bit architectures don't
implement generally. This uses ktime_to_us() and ktime_to_ms()
instead.

The time abstraction needs i64 / u32 division so C's div_s64() can be
used but ktime_to_us() and ktime_to_ms() provide a simpler solution
for this time abstraction problem on 32-bit architectures.

32-bit ARM is the only 32-bit architecture currently supported by
Rust. Using the cfg attribute, only 32-bit architectures will call
ktime_to_us() and ktime_to_ms(), while the other 64-bit architectures
will continue to use the current code as-is to avoid the overhead.

One downside of calling the C's functions is that the as_micros/millis
methods can no longer be const fn. We stick with the simpler approach
unless there's a compelling need for a const fn.

Suggested-by: default avatarArnd Bergmann <arnd@arndb.de>
Suggested-by: default avatarBoqun Feng <boqun.feng@gmail.com>
Signed-off-by: default avatarFUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: default avatarAndreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250502004524.230553-1-fujita.tomonori@gmail.com


Signed-off-by: default avatarAndreas Hindborg <a.hindborg@kernel.org>
parent e04c78d8

rust/helpers/helpers.c

+1 −0
Original line number Diff line number Diff line
@@ -40,6 +40,7 @@ 
#include "spinlock.c"

#include "sync.c"

#include "task.c"

#include "time.c"

#include "uaccess.c"

#include "vmalloc.c"

#include "wait.c"

rust/helpers/time.c

0 → 100644
+13 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0



#include <linux/ktime.h>



s64 rust_helper_ktime_to_us(const ktime_t kt)

{

	return ktime_to_us(kt);

}



s64 rust_helper_ktime_to_ms(const ktime_t kt)

{

	return ktime_to_ms(kt);

}

rust/kernel/time.rs

+22 −4
Original line number Diff line number Diff line
@@ -228,13 +228,31 @@ pub const fn as_nanos(self) -> i64 { 
    /// Return the smallest number of microseconds greater than or equal

    /// to the value in the [`Delta`].

    #[inline]

    pub const fn as_micros_ceil(self) -> i64 {

    pub fn as_micros_ceil(self) -> i64 {

        #[cfg(CONFIG_64BIT)]

        {

            self.as_nanos().saturating_add(NSEC_PER_USEC - 1) / NSEC_PER_USEC

        }



        #[cfg(not(CONFIG_64BIT))]

        // SAFETY: It is always safe to call `ktime_to_us()` with any value.

        unsafe {

            bindings::ktime_to_us(self.as_nanos().saturating_add(NSEC_PER_USEC - 1))

        }

    }



    /// Return the number of milliseconds in the [`Delta`].

    #[inline]

    pub const fn as_millis(self) -> i64 {

    pub fn as_millis(self) -> i64 {

        #[cfg(CONFIG_64BIT)]

        {

            self.as_nanos() / NSEC_PER_MSEC

        }



        #[cfg(not(CONFIG_64BIT))]

        // SAFETY: It is always safe to call `ktime_to_ms()` with any value.

        unsafe {

            bindings::ktime_to_ms(self.as_nanos())

        }

    }

}