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

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Message-ID: <549095b9-c12e-4415-999a-f2589451f5e0@amd.com>
Date: Fri, 16 Jan 2026 10:20:32 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Viresh Kumar <viresh.kumar@...aro.org>
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()

Hello Viresh,

On 1/16/2026 10:14 AM, Viresh Kumar wrote:
> 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.

Ack! Let me give it a spin before sending out the v3. Thank you again
for taking a look.

-- 
Thanks and Regards,
Prateek