Re: [PATCH v4] ARM: smp: Only expose /sys/.../cpuX/online if hotpluggable

From: Simon Horman
Date: Tue Apr 07 2015 - 21:06:21 EST

On Tue, Apr 07, 2015 at 03:56:35PM +0100, Russell King - ARM Linux wrote:
> On Mon, Apr 06, 2015 at 01:24:13PM -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@xxxxxxx>
> > Cc: Nicolas Pitre <nico@xxxxxxxxxx>
> > Cc: Dave Martin <Dave.Martin@xxxxxxx>
> > Cc: Simon Horman <horms@xxxxxxxxxxxx>
> > Cc: Magnus Damm <magnus.damm@xxxxxxxxx>
> > Cc: <linux-sh@xxxxxxxxxxxxxxx>
> > Cc: Tyler Baker <tyler.baker@xxxxxxxxxx>
> > Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> I think this is fine, but I'd like to see some acks for it. As it's
> mostly core ARM stuff, it should be merged through my tree unless there
> is a known conflict with arm-soc. Thanks.

I'm happy with the shmobile portions and have verified that
they don't conflict with anything I have queued up for v4.1.

So in the context of that release, for the shmobile portion:

Acked-by: Simon Horman <horms+renesas@xxxxxxxxxxxx>

I also tested, and the effected shmobile boards still seem to boot
with this patch applied.

Tested-by: Simon Horman <horms+renesas@xxxxxxxxxxxx>
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