linux-kernel - Re: [PATCH v2 2/2] cpuidle: Change :enter_dead() driver callback return type to void

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Message-ID: <6efcfc19-bdf7-4c31-9a18-275dce6b750d@amd.com>
Date: Tue, 19 Nov 2024 10:05:20 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: "Gautham R. Shenoy" <gautham.shenoy@....com>,
 "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux PM <linux-pm@...r.kernel.org>, Peter Zijlstra
 <peterz@...radead.org>, LKML <linux-kernel@...r.kernel.org>,
 x86 Maintainers <x86@...nel.org>,
 Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>,
 Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
 Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] cpuidle: Change :enter_dead() driver callback
 return type to void

On 11/19/2024 09:09, Gautham R. Shenoy wrote:
> Hello Rafael,
> 
> On Fri, Nov 15, 2024 at 10:00:25PM +0100, Rafael J. Wysocki wrote:
>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>
>> After a previous change, cpuidle_play_dead(), which is the only caller
>> of idle state :enter_dead() callbacks, ignores their return values, so
>> they may as well be void.
>>
>> Suggested-by: Peter Zijlstra <peterz@...radead.org>
>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
>> ---
>>
>> v1 -> v2: New patch
>>
>> Interestingly enough, the only user of :enter_dead() idle state callbacks
>> in the current mainline turns out to be ACPI idle.
> 
> For that matter, the only user of cpuidle_play_dead() is the
> native_play_dead(). Was that always the case?
> 
> Some of the other architectures select the deepest available idle
> state at boot time, and enter that state when a CPU is offlined.
> 
> In any case I am ok with this.
> 
> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>
Reviewed-by: Mario Limonciello <mario.limonciello@....com>

> --
> Thanks and Regards
> gautham.
>>
>> ---
>>   drivers/acpi/processor_idle.c |    7 ++-----
>>   include/linux/cpuidle.h       |    2 +-
>>   2 files changed, 3 insertions(+), 6 deletions(-)
>>
>> Index: linux-pm/include/linux/cpuidle.h
>> ===================================================================
>> --- linux-pm.orig/include/linux/cpuidle.h
>> +++ linux-pm/include/linux/cpuidle.h
>> @@ -61,7 +61,7 @@ struct cpuidle_state {
>>   			struct cpuidle_driver *drv,
>>   			int index);
>>   
>> -	int (*enter_dead) (struct cpuidle_device *dev, int index);
>> +	void (*enter_dead) (struct cpuidle_device *dev, int index);
>>   
>>   	/*
>>   	 * CPUs execute ->enter_s2idle with the local tick or entire timekeeping
>> Index: linux-pm/drivers/acpi/processor_idle.c
>> ===================================================================
>> --- linux-pm.orig/drivers/acpi/processor_idle.c
>> +++ linux-pm/drivers/acpi/processor_idle.c
>> @@ -578,7 +578,7 @@ static void __cpuidle acpi_idle_do_entry
>>    * @dev: the target CPU
>>    * @index: the index of suggested state
>>    */
>> -static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
>> +static void acpi_idle_play_dead(struct cpuidle_device *dev, int index)
>>   {
>>   	struct acpi_processor_cx *cx = per_cpu(acpi_cstate[index], dev->cpu);
>>   
>> @@ -591,11 +591,8 @@ static int acpi_idle_play_dead(struct cp
>>   		else if (cx->entry_method == ACPI_CSTATE_SYSTEMIO) {
>>   			io_idle(cx->address);
>>   		} else
>> -			return -ENODEV;
>> +			return;
>>   	}
>> -
>> -	/* Never reached */
>> -	return 0;
>>   }
>>   
>>   static __always_inline bool acpi_idle_fallback_to_c1(struct acpi_processor *pr)
>>
>>
>>