Re: [PATCH 1/2] rust: clk: Add ExclusiveClk wrapper for clk_rate_exclusive_get

[Alice Ryhl <aliceryhl@google.com>]

On Tue, May 26, 2026 at 07:04:57PM +0200, Maurice Hieronymus via B4 Relay wrote:
> From: Maurice Hieronymus <mhi@mailbox.org>
> 
> Add Rust bindings for clk_rate_exclusive_get() and
> clk_rate_exclusive_put().
> 
> Clk::rate_exclusive_get() consumes the Clk and returns an ExclusiveClk;
> the matching put is issued from its Drop impl. ExclusiveClk derefs to
> Clk so existing rate / prepare / enable APIs remain available on the
> locked handle.
> 
> Signed-off-by: Maurice Hieronymus <mhi@mailbox.org>

Overall looks okay to me. With below comments fixed:
Reviewed-by: Alice Ryhl <aliceryhl@google.com>

>  rust/kernel/clk.rs | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 65 insertions(+)
> 
> diff --git a/rust/kernel/clk.rs b/rust/kernel/clk.rs
> index 7abbd0767d8c..8cda40cb01e4 100644
> --- a/rust/kernel/clk.rs
> +++ b/rust/kernel/clk.rs
> @@ -249,6 +249,23 @@ pub fn set_rate(&self, rate: Hertz) -> Result {
>              // [`clk_set_rate`].
>              to_result(unsafe { bindings::clk_set_rate(self.as_raw(), rate.as_hz()) })
>          }
> +
> +        /// Acquire exclusive control over the clock's rate.
> +        ///
> +        /// Consumes the [`Clk`] and returns an [`ExclusiveClk`] that releases the exclusivity
> +        /// when dropped. While held, no other consumer may change the clock's rate.
> +        ///
> +        /// Equivalent to the kernel's [`clk_rate_exclusive_get`] API. Must not be called from
> +        /// atomic context.
> +        ///
> +        /// [`clk_rate_exclusive_get`]:
> +        /// https://docs.kernel.org/core-api/kernel-api.html#c.clk_rate_exclusive_get

Avoid the newline here. Links are long, and it's okay that they are
long. They must be on one line.

> +        pub fn rate_exclusive_get(self) -> Result<ExclusiveClk> {
> +            // SAFETY: By the type invariants, self.as_raw() is a valid argument for
> +            // [`clk_rate_exclusive_get`].
> +            to_result(unsafe { bindings::clk_rate_exclusive_get(self.as_raw()) })?;
> +            Ok(ExclusiveClk(self))
> +        }
>      }
>  
>      impl Drop for Clk {
> @@ -329,6 +346,54 @@ fn deref(&self) -> &Clk {
>              &self.0
>          }
>      }
> +
> +    /// A [`Clk`] with exclusive control over its rate.
> +    ///
> +    /// While an [`ExclusiveClk`] exists, no other consumer of the same clock may change its rate.
> +    /// Obtained by calling [`Clk::rate_exclusive_get`]; the exclusivity is released automatically
> +    /// when the value is dropped, after which the inner [`Clk`] is dropped as usual.
> +    ///
> +    /// # Invariants
> +    ///
> +    /// An [`ExclusiveClk`] instance owns a [`Clk`] for which `clk_rate_exclusive_get` has been
> +    /// called and the matching `clk_rate_exclusive_put` has not yet been called.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```
> +    /// use kernel::clk::{Clk, ExclusiveClk};
> +    /// use kernel::device::Device;
> +    /// use kernel::error::Result;
> +    ///
> +    /// fn lock_rate(dev: &Device) -> Result<ExclusiveClk> {
> +    ///     let clk = Clk::get(dev, None)?;
> +    ///     clk.prepare_enable()?;
> +    ///     clk.rate_exclusive_get()
> +    /// }
> +    /// ```
> +    ///
> +    /// [`struct clk`]: https://docs.kernel.org/driver-api/clk.html

Unused link.

> +    pub struct ExclusiveClk(Clk);
> +
> +    // Make [`ExclusiveClk`] behave like [`Clk`].
> +    impl Deref for ExclusiveClk {
> +        type Target = Clk;
> +
> +        fn deref(&self) -> &Clk {
> +            &self.0
> +        }
> +    }
> +
> +    impl Drop for ExclusiveClk {
> +        fn drop(&mut self) {
> +            // SAFETY: By the type invariants, self.as_raw() is a valid argument for
> +            // [`clk_rate_exclusive_put`] and balances the [`clk_rate_exclusive_get`] call from
> +            // [`Clk::rate_exclusive_get`].
> +            unsafe {
> +                bindings::clk_rate_exclusive_put(self.as_raw());
> +            }

Nit: usually we format this with the semicolon outside the unsafe block.

unsafe { bindings::clk_rate_exclusive_put(self.as_raw()) };

Alice