Re: [PATCH v4 19/20] rust: time: add arch_timer_get_rate wrapper

[Alice Ryhl]

On Sat, Apr 25, 2026 at 1:39 AM Deborah Brouwer
<deborah.brouwer@xxxxxxxxxxxxx> wrote:
>
> Provide a safe Rust wrapper for arch_timer_get_rate().
>
> The underlying C helper returns 0 when the ARM architectural timer
> is not available or not yet initialized. Map this to Option<u32> to
> make the absence of a valid rate explicit to Rust callers.
>
> This allows Rust drivers to query the system timer frequency and
> select appropriate time sources when programming hardware timeouts.
>
> Signed-off-by: Deborah Brouwer <deborah.brouwer@xxxxxxxxxxxxx>
> ---
>  rust/kernel/time.rs | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
>
> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> index 6ea98dfcd027..03ce96450fc8 100644
> --- a/rust/kernel/time.rs
> +++ b/rust/kernel/time.rs
> @@ -359,6 +359,35 @@ fn div(self, rhs: Self) -> Self::Output {
>      }
>  }
>
> +/// Returns the ARM architecture timer frequency in Hz, if available.
> +///
> +/// This function queries the system-wide ARM architecture timer frequency.
> +/// The architecture timer provides a consistent time source across all CPU cores.
> +///
> +/// Returns `None` if:
> +/// - The ARM architecture timer is not available (`CONFIG_ARM_ARCH_TIMER` not enabled)
> +/// - The timer rate is zero (not initialized)
> +///
> +/// # Examples
> +///
> +/// ```
> +/// use kernel::time::arch_timer_get_rate;
> +///
> +/// if let Some(rate) = arch_timer_get_rate() {
> +///     // Use `rate`.
> +/// }
> +/// ```
> +pub fn arch_timer_get_rate() -> Option<u32> {
> +    // SAFETY: The C API is available in all configs; when CONFIG_ARM_ARCH_TIMER
> +    // is disabled, the header provides a stub returning 0.

The stub is inline, so to call it you must define a helper for this
function. This code will not compile if CONFIG_ARM_ARCH_TIMER is not
set.

Alice