From mboxrd@z Thu Jan  1 00:00:00 1970
From: mark.rutland@arm.com (Mark Rutland)
Date: Fri, 26 Sep 2014 14:20:38 +0100
Subject: [PATCH 1/3] arm: ls1: add CPU hotplug platform support
In-Reply-To: <20140926130311.GQ5182@n2100.arm.linux.org.uk>
References: <1411730703-25836-1-git-send-email-chenhui.zhao@freescale.com>
 <1411730703-25836-2-git-send-email-chenhui.zhao@freescale.com>
 <20140926122003.GP5182@n2100.arm.linux.org.uk>
 <20140926124614.GD7422@leverpostej>
 <20140926130311.GQ5182@n2100.arm.linux.org.uk>
Message-ID: <20140926132038.GF7422@leverpostej>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

> > This looks to be a carbon copy of the vexpress pseudo-hotplug in
> > arch/arm/mach-vexpress/hotplug.c, which is obviously broken in the way
> > you describe above. Perhaps we should go about ripping that out?
> 
> The Versatile Express does not support suspend so the only problem case
> is kexec.  However, isn't this support needed for big.LITTLE, and as
> the Versatile Express is the platform which these features get developed
> on, having working CPU hotplug seems rather fundamental for ARM kernel
> feature development.
> 
> In that regard, Versatile Express is something of a special case.

It is admittedly helpful during development to perform pseudo-hotplug on
Versatile Express. I have a local patch adding vexpress_cpu_disable so I
can test for bugs that only trigger if CPU0 is hotplugged.

Given that, perhaps we should make it clearer that Versatile Express is
not a reference implementation for CPU hotplug; add some Kconfig (e.g.
VEXPRESS_PSEUDO_HOTPLUG) that depends on !KEXEC && !SUSPEND, and putting
a note in hotplug.c stating it's not suitable as a reference
implementation.

...but perhaps that's overkill.

Mark.