linux-kernel - Re: [PATCH v2 2/2] cpufreq: Pass the policy to cpufreq_driver->adjust

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Message-ID: <rs4z34vntq4inwbl6nhzwsmefcgud33a4jpec44ff5ylrxtnur@rczzlmhgejky>
Date: Fri, 16 Jan 2026 10:14:55 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Huang Rui <ray.huang@....com>, 
	"Gautham R. Shenoy" <gautham.shenoy@....com>, Mario Limonciello <mario.limonciello@....com>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, 
	Len Brown <lenb@...nel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Clark Williams <clrkwllms@...nel.org>, Bert Karwatzki <spasswolf@....de>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, Perry Yuan <perry.yuan@....com>
Subject: Re: [PATCH v2 2/2] cpufreq: Pass the policy to
 cpufreq_driver->adjust_perf()

On 16-01-26, 10:08, K Prateek Nayak wrote:
> Guilty of not having CONFIG_RUST enabled! I've arrived at the
> following after tasking a look at cpufreq.rs (specifically the
> fast_switch_callback implementation):
> 
>   (Only build tested currently)
> 
> diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs
> index f968fbd22890..bea109f8ff78 100644
> --- a/rust/kernel/cpufreq.rs
> +++ b/rust/kernel/cpufreq.rs
> @@ -1255,18 +1255,17 @@ impl<T: Driver> Registration<T> {
>      /// # Safety
>      ///
>      /// - This function may only be called from the cpufreq C infrastructure.
> +    /// - The pointer arguments must be valid pointers.
>      unsafe extern "C" fn adjust_perf_callback(
> -        cpu: c_uint,
> +        ptr: *mut bindings::cpufreq_policy,
>          min_perf: c_ulong,
>          target_perf: c_ulong,
>          capacity: c_ulong,
>      ) {
> -        // SAFETY: The C API guarantees that `cpu` refers to a valid CPU number.
> -        let cpu_id = unsafe { CpuId::from_u32_unchecked(cpu) };
> -
> -        if let Ok(mut policy) = PolicyCpu::from_cpu(cpu_id) {
> -            T::adjust_perf(&mut policy, min_perf, target_perf, capacity);
> -        }
> +        // SAFETY: The `ptr` is guaranteed to be valid by the contract with the C code for the
> +        // lifetime of `policy`.
> +        let policy = unsafe { Policy::from_raw_mut(ptr) };
> +        T::adjust_perf(policy, min_perf, target_perf, capacity);
>      }
>  
>      /// Driver's `get_intermediate` callback.
> ---
> 
> Let me know what you think. If you think this is alright, I'll fold it
> into this same patch in the next version to preserve bisectiblity with
> CONFIG_RUST (or should I keep it separate?).
> 
> Since this is my first time dealing with the rust bindings, comments are
> highly appreciated.

Yeah looks fine. Just make sure it builds fine.

-- 
viresh