Re: [PATCH v3] ARM: smp: Only expose /sys/.../cpuX/online if hotpluggable

From: Stephen Boyd <sboyd@codeaurora.org>
To: Simon Horman <horms@verge.net.au>
Cc: Russell King <linux@arm.linux.org.uk>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Mark Rutland <mark.rutland@arm.com>,
	Nicolas Pitre <nico@linaro.org>,
	Dave Martin <Dave.Martin@arm.com>,
	Magnus Damm <magnus.damm@gmail.com>,
	linux-sh@vger.kernel.org
Subject: Re: [PATCH v3] ARM: smp: Only expose /sys/.../cpuX/online if hotpluggable
Date: Wed, 18 Feb 2015 15:27:57 -0800	[thread overview]
Message-ID: <54E51FFD.7080506@codeaurora.org> (raw)
In-Reply-To: <20150218222731.GC24177@verge.net.au>

On 02/18/15 14:27, Simon Horman wrote:
> On Fri, Feb 13, 2015 at 04:42:54PM -0800, 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 current users use the op to
>> indicate if a CPU can be hotplugged or not in a static fashion.
>> With PSCI we may need to introduce 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 1, 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@arm.com>
>> Cc: Nicolas Pitre <nico@linaro.org>
>> Cc: Dave Martin <Dave.Martin@arm.com>
>> Cc: Simon Horman <horms@verge.net.au>
>> Cc: Magnus Damm <magnus.damm@gmail.com>
>> Cc: <linux-sh@vger.kernel.org>
>> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
>> ---
>>
>> Changes since v2:
>>  * Left cpu_disable op in place
>>  * Split out shmobile function deletion
>>
>>  arch/arm/common/mcpm_platsmp.c       | 12 ++++--------
>>  arch/arm/include/asm/smp.h           | 10 ++++++++++
>>  arch/arm/kernel/setup.c              |  2 +-
>>  arch/arm/kernel/smp.c                | 15 ++++++++++++++-
>>  arch/arm/mach-shmobile/common.h      |  2 +-
>>  arch/arm/mach-shmobile/platsmp.c     |  4 ++--
>>  arch/arm/mach-shmobile/smp-r8a7790.c |  2 +-
>>  arch/arm/mach-shmobile/smp-r8a7791.c |  2 +-
>>  arch/arm/mach-shmobile/smp-sh73a0.c  |  2 +-
>>  9 files changed, 35 insertions(+), 16 deletions(-)
> I think it would make sense to separate the ARM-core changes
> from the mach-shmobile integration changes.

Are you saying two (three?) patches to add the op, and then move over
each struct smp_operations? It's all going through rmk's tree so I'll
leave that up to him.

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