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

[Onur Özkan]

On Fri, 24 Apr 2026 16:39:13 -0700
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)

Can we return distinct errors for these cases and return NonZero<u32> when the
rate is valid?

> +///
> +/// # 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.
> +    let rate = unsafe { bindings::arch_timer_get_rate() };
> +    if rate == 0 {
> +        None
> +    } else {
> +        Some(rate)
> +    }
> +}
> +
>  impl Delta {
>      /// A span of time equal to zero.
>      pub const ZERO: Self = Self { nanos: 0 };
> 
> -- 
> 2.53.0
>