linux-kernel - Re: [PATCH] arm: platsmp: Allow secondary cpu hotplug with maxcpus=1

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Date:	Thu, 30 Jun 2011 14:38:52 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-sh@...r.kernel.org, linux-tegra@...r.kernel.org,
	Kukjin Kim <kgene.kim@...sung.com>,
	David Brown <davidb@...eaurora.org>,
	Tony Lindgren <tony@...mide.com>,
	Srinidhi Kasagar <srinidhi.kasagar@...ricsson.com>,
	Linus Walleij <linus.walleij@...ricsson.com>
Subject: Re: [PATCH] arm: platsmp: Allow secondary cpu hotplug with maxcpus=1

On Wed, Jun 29, 2011 at 11:31:39AM -0700, Stephen Boyd wrote:
> If an ARM system has multiple cpus in the same socket and the
> kernel is booted with maxcpus=1, secondary cpus are possible but
> not present due to how platform_smp_prepare_cpus() is called.
> Fix this by always calling platform_smp_prepare_cpus() as long as
> max_cpus is non-zero (0 means no SMP) to allow platform code to
> decide if any non-boot cpus are present in the system. Since
> all current platform code doesn't support physical hotplug we
> have a situation where possible == present and thus we can
> simply copy the possible map to the present map.
> 
> With this patch it's possible to boot an ARM system with
> maxcpus=1 on the command line and then hotplug in secondary cpus
> via sysfs. This is more in line with how x86 works with maxcpus=1
> on the command line.
> 
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>

Acked-by: Paul Mundt <lethal@...ux-sh.org>
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