linux-kernel - Re: [PATCH v5] ARM: smp: Only expose /sys/.../cpuX/online if hotpluggable

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Date:	Tue, 09 Jun 2015 12:08:28 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Mark Rutland <mark.rutland@....com>,
	Nicolas Pitre <nico@...aro.org>,
	Tyler Baker <tyler.baker@...aro.org>, linux-sh@...r.kernel.org,
	Magnus Damm <magnus.damm@...il.com>,
	linux-kernel@...r.kernel.org, Simon Horman <horms@...ge.net.au>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Dave Martin <Dave.Martin@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5] ARM: smp: Only expose /sys/.../cpuX/online if hotpluggable

On 04/13/2015 06:42 AM, Russell King - ARM Linux wrote:
> On Fri, Apr 10, 2015 at 03:33:11PM -0700, Stephen Boyd wrote:
>> Writes to /sys/.../cpuX/online fail if we determine the platform
>> doesn't support hotplug for that CPU. Furthermore, if the cpu_die
>> op isn't specified the system hangs when we try to offline a CPU
>> and it comes right back online unexpectedly. Let's figure this
>> stuff out before we make the sysfs nodes so that the online file
>> doesn't even exist if it isn't (at least sometimes) possible to
>> hotplug the CPU.
>>
>> Add a new 'cpu_can_disable' op and repoint all 'cpu_disable'
>> implementations at it because all implementers use the op to
>> indicate if a CPU can be hotplugged or not in a static fashion.
>> With PSCI we may need to add a 'cpu_disable' op so that the
>> secure OS can be migrated off the CPU we're trying to hotplug.
>> In this case, the 'cpu_can_disable' op will indicate that all
>> CPUs are hotpluggable by returning true, but the 'cpu_disable' op
>> will make a PSCI migration call and occasionally fail, denying
>> the hotplug of a CPU. This shouldn't be any worse than x86 where
>> we may indicate that all CPUs are hotpluggable but occasionally
>> we can't offline a CPU due to check_irq_vectors_for_cpu_disable()
>> failing to find a CPU to move vectors to.
>>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: Nicolas Pitre <nico@...aro.org>
>> Cc: Dave Martin <Dave.Martin@....com>
>> Acked-by: Simon Horman <horms@...ge.net.au> [shmobile portion]
>> Tested-by: Simon Horman <horms@...ge.net.au>
>> Cc: Magnus Damm <magnus.damm@...il.com>
>> Cc: <linux-sh@...r.kernel.org>
>> Cc: Tyler Baker <tyler.baker@...aro.org>
>> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
>> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> Let's see some more acks for this...
>

Nobody else has acked this so far. Shall I put it in the patch tracker
now? Or is there someone more specific we need an ack from?

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

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