[PATCH 7/9] rust: time: add arch_timer_get_rate wrapper

[Laura Nao <laura.nao@collabora.com>]

From: Deborah Brouwer <deborah.brouwer@collabora.com>

Provide a safe Rust wrapper for arch_timer_get_rate().

The Rust binding calls a C helper that 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@collabora.com>
Signed-off-by: Laura Nao <laura.nao@collabora.com>
---
 rust/helpers/time.c |  6 ++++++
 rust/kernel/time.rs | 30 ++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/rust/helpers/time.c b/rust/helpers/time.c
index 32f495970493..70fda31bd758 100644
--- a/rust/helpers/time.c
+++ b/rust/helpers/time.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 
+#include <clocksource/arm_arch_timer.h>
 #include <linux/delay.h>
 #include <linux/ktime.h>
 #include <linux/timekeeping.h>
@@ -38,3 +39,8 @@ __rust_helper void rust_helper_udelay(unsigned long usec)
 {
 	udelay(usec);
 }
+
+__rust_helper u32 rust_helper_arch_timer_get_rate(void)
+{
+	return arch_timer_get_rate();
+}
diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
index 6c0a5e8090d0..6c48ce21984a 100644
--- a/rust/kernel/time.rs
+++ b/rust/kernel/time.rs
@@ -423,6 +423,36 @@ 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 helper is available in all configs; it calls
+    // `arch_timer_get_rate()`, which falls back to an inline stub returning 0
+    // when CONFIG_ARM_ARCH_TIMER is disabled.
+    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 { value: 0 };

-- 
2.39.5