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

[Deborah Brouwer]

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.
+    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