linux-kernel - Re: [PATCH v2] ARM: smp: Only expose /sys/.../cpuX/online if hotpluggable

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Date:	Fri, 13 Feb 2015 12:23:22 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Simon Horman <horms@...ge.net.au>
CC:	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Mark Rutland <mark.rutland@....com>,
	Nicolas Pitre <nico@...aro.org>,
	Dave Martin <Dave.Martin@....com>,
	Magnus Damm <magnus.damm@...il.com>, linux-sh@...r.kernel.org
Subject: Re: [PATCH v2] ARM: smp: Only expose /sys/.../cpuX/online if hotpluggable

On 02/13/15 12:20, Simon Horman wrote:
> Hi Stephen,
>
> On Fri, Feb 13, 2015 at 10:06:39AM -0800, Stephen Boyd wrote:
>> diff --git a/arch/arm/mach-shmobile/smp-r8a7779.c b/arch/arm/mach-shmobile/smp-r8a7779.c
>> index 3f761f839043..b45206f93ddf 100644
>> --- a/arch/arm/mach-shmobile/smp-r8a7779.c
>> +++ b/arch/arm/mach-shmobile/smp-r8a7779.c
>> @@ -124,19 +124,12 @@ static int r8a7779_cpu_kill(unsigned int cpu)
>>  
>>  	return 0;
>>  }
>> -
>> -static int r8a7779_cpu_disable(unsigned int cpu)
>> -{
>> -	/* only CPU1->3 have power domains, do not allow hotplug of CPU0 */
>> -	return cpu == 0 ? -EPERM : 0;
>> -}
>>  #endif /* CONFIG_HOTPLUG_CPU */
>>  
>>  struct smp_operations r8a7779_smp_ops  __initdata = {
>>  	.smp_prepare_cpus	= r8a7779_smp_prepare_cpus,
>>  	.smp_boot_secondary	= r8a7779_boot_secondary,
>>  #ifdef CONFIG_HOTPLUG_CPU
>> -	.cpu_disable		= r8a7779_cpu_disable,
>>  	.cpu_die		= shmobile_smp_scu_cpu_die,
>>  	.cpu_kill		= r8a7779_cpu_kill,
>>  #endif
> Its not clear to me why r8a7779_cpu_disable() has been
> removed rather than replaced by r8a7779_cpu_can_disable()

By default ARM's smp.c assumes that CPU0 can't be hotplugged. The
function is redundant. I guess I should have mentioned that in the
commit text.

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

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