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

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Message-ID: <20150213225854.GG8656@n2100.arm.linux.org.uk>
Date:	Fri, 13 Feb 2015 22:58:54 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Magnus Damm <magnus.damm@...il.com>
Cc:	Stephen Boyd <sboyd@...eaurora.org>,
	Simon Horman <horms@...ge.net.au>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mark Rutland <mark.rutland@....com>,
	Nicolas Pitre <nico@...aro.org>,
	Dave Martin <Dave.Martin@....com>,
	SH-Linux <linux-sh@...r.kernel.org>
Subject: Re: [PATCH v2] ARM: smp: Only expose /sys/.../cpuX/online if
 hotpluggable

On Fri, Feb 13, 2015 at 08:54:22PM +0000, Magnus Damm wrote:
> Thanks for your efforts. Can you please tell me where that limitation
> is located? I'm quite sure I've brought CPU cores up and down
> including CPU0, but maybe something is missing?

If you don't provide a cpu_disable function, by default only the non-boot
(iow, non-CPU0) CPUs can be hotplugged.

If you provide a cpu_disable function, it can instruct the system that
fewer or more CPUs can be hotplugged, including the boot CPU.  The system
will then restrict you to a minimum of any one CPU online.

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