From mboxrd@z Thu Jan  1 00:00:00 1970
From: marc_gonzalez@sigmadesigns.com (Marc Gonzalez)
Date: Wed, 29 Jun 2016 14:28:23 +0200
Subject: [PATCH v3 1/2] ARM: tango: add HOTPLUG_CPU support
In-Reply-To: <577294E2.5030405@arm.com>
References: <57726597.8030501@sigmadesigns.com>
 <577266AD.8000006@sigmadesigns.com> <57726DE0.8090308@arm.com>
 <577291F1.8060105@sigmadesigns.com> <577294E2.5030405@arm.com>
Message-ID: <5773BEE7.4080501@sigmadesigns.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 28/06/2016 17:16, Robin Murphy wrote:

> On 28/06/16 16:04, Marc Gonzalez wrote:
>
>> On 28/06/2016 14:30, Robin Murphy wrote:
>>
>>> Does the firmware guarantee that this will succeed (or at least report
>>> success) in finite time, regardless of how messed up the system might
>>> be? I'd imagine this should probably have either a timeout or a comment
>>> clarifying why it doesn't need a timeout.
>>
>> Good point.
>>
>> The FW allows only one thread at a time. If a thread is wedged inside
>> the FW, no other thread can use the FW. In that situation, cpu0 would
>> remain stuck inside tango_cpu_kill().
>>
>> Note, that if tango_cpu_kill() starts failing, then secondary cores
>> will remain "zombies". So the system is mostly hosed anyway...
>> Only cpu0 will be available.
> 
> Indeed; my thought was that if CPU1 somehow ends up wedged such that
> tango_aux_core_die() never completes, then CPU0 eventually timing out
> and being able to limp through a clean(ish) reboot is probably
> preferable to spinning in cpu_kill() forever.

I have sent an updated patch addressing your comment.
Thanks for flagging the issue.

Regards.