linux-kernel - Re: [PATCH v2] ARM: Don't use complete() during __cpu

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Message-ID: <54DA7CEC.7020606@codeaurora.org>
Date:	Tue, 10 Feb 2015 13:49:32 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Mark Rutland <mark.rutland@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>
Subject: Re: [PATCH v2] ARM: Don't use complete() during __cpu_die

On 02/10/15 13:15, Russell King - ARM Linux wrote:
> On Tue, Feb 10, 2015 at 01:04:30PM -0800, Stephen Boyd wrote:
>> From: Stephen Boyd <sboyd@...eaurora.org>
>> Subject: [PATCH] ARM: smp: Only expose /sys/.../cpuX/online if hotpluggable
>>
>> Writes to /sys/.../cpuX/online fail if we determine the platform
>> doesn't support hotplug for that CPU. Let's figure this out
>> befoer we make the sysfs nodes so that the online file doesn't
>> even exist if it's not possible to hotplug the CPU.
>>
>> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
>> ---
>>  arch/arm/include/asm/smp.h |  6 ++++++
>>  arch/arm/kernel/setup.c    |  2 +-
>>  arch/arm/kernel/smp.c      | 11 ++++-------
>>  3 files changed, 11 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h
>> index 18f5a554134f..9f82430efd59 100644
>> --- a/arch/arm/include/asm/smp.h
>> +++ b/arch/arm/include/asm/smp.h
>> @@ -123,4 +123,10 @@ struct of_cpu_method {
>>   */
>>  extern void smp_set_ops(struct smp_operations *);
>>  
>> +#ifdef CONFIG_HOTPLUG_CPU
>> +extern int platform_can_hotplug_cpu(unsigned int cpu);
>> +#else
>> +static inline int platform_can_hotplug_cpu(unsigned int cpu) { return 0; }
> Please split this across four lines like a normal function.
>

Ok.

>> +#endif
>> +
>>  #endif /* ifndef __ASM_ARM_SMP_H */
>> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
>> index 715ae19bc7c8..c61c09defc78 100644
>> --- a/arch/arm/kernel/setup.c
>> +++ b/arch/arm/kernel/setup.c
>> @@ -974,7 +974,7 @@ static int __init topology_init(void)
>>  
>>  	for_each_possible_cpu(cpu) {
>>  		struct cpuinfo_arm *cpuinfo = &per_cpu(cpu_data, cpu);
>> -		cpuinfo->cpu.hotpluggable = 1;
>> +		cpuinfo->cpu.hotpluggable = platform_can_hotplug_cpu(cpu);
>>  		register_cpu(&cpuinfo->cpu, cpu);
>>  	}
>>  
>> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
>> index fe0386c751b2..4d213b24db60 100644
>> --- a/arch/arm/kernel/smp.c
>> +++ b/arch/arm/kernel/smp.c
>> @@ -174,18 +174,19 @@ static int platform_cpu_kill(unsigned int cpu)
>>  	return 1;
>>  }
>>  
>> -static int platform_cpu_disable(unsigned int cpu)
>> +int platform_can_hotplug_cpu(unsigned int cpu)
>>  {
>>  	if (smp_ops.cpu_disable)
>> -		return smp_ops.cpu_disable(cpu);
>> +		return smp_ops.cpu_disable(cpu) ? 0 : 1;
>>  
>>  	/*
>>  	 * By default, allow disabling all CPUs except the first one,
>>  	 * since this is special on a lot of platforms, e.g. because
>>  	 * of clock tick interrupts.
>>  	 */
>> -	return cpu == 0 ? -EPERM : 0;
>> +	return cpu == 0 ? 0 : 1;
>>  }
>> +
>>  /*
>>   * __cpu_disable runs on the processor to be shutdown.
>>   */
>> @@ -194,10 +195,6 @@ int __cpu_disable(void)
>>  	unsigned int cpu = smp_processor_id();
>>  	int ret;
>>  
>> -	ret = platform_cpu_disable(cpu);
>> -	if (ret)
>> -		return ret;
>> -
> I would much rather prefer smp_ops.cpu_disable() to be renamed in this
> case - name it smp_ops.cpu_can_disable() so that it's clear that it's
> no longer part of the __cpu_disable() path.

Sure. That also makes the  ? 0 : 1 thing go away.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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