From mboxrd@z Thu Jan  1 00:00:00 1970
From: josephl@nvidia.com (Joseph Lo)
Date: Fri, 17 May 2013 18:15:59 +0800
Subject: [PATCH 0/6] ARM: tegra114: add CPU hotplug support
In-Reply-To: <51952344.1090003@wwwdotorg.org>
References: <1368613644-11863-1-git-send-email-josephl@nvidia.com>
 <51941C58.9060002@wwwdotorg.org>
 <1368698019.7403.10.camel@jlo-ubuntu-64.nvidia.com>
 <51952344.1090003@wwwdotorg.org>
Message-ID: <1368785759.3174.8.camel@jlo-ubuntu-64.nvidia.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, 2013-05-17 at 02:19 +0800, Stephen Warren wrote:
> On 05/16/2013 03:53 AM, Joseph Lo wrote:
> > On Thu, 2013-05-16 at 07:38 +0800, Stephen Warren wrote:
> >> On 05/15/2013 04:27 AM, Joseph Lo wrote:
> >>> Tegra 114 is different with other Tegra SoC chips. It using ARM Cortex-A15
> >>> as CPU core and a enhanced flow controller for CPU power control. So
> >>> we need to skip some code that was for Contex-A9 and some other support
> >>> code that was for other Tegra SoC chips. Then adding the proper power up
> >>> and hot plug control for Tegra114.
> >>
> >> This series mostly works OK, but I see one problem: I can't hotunplug
> >> CPU0, which the commit descriptions and code changes imply I should be
> >> able to do:
> >>
> >> root at localhost:~# echo 0 > /sys/devices/system/cpu/cpu0/online
> >> -bash: echo: write error: Operation not permitted
> > 
> > I want to provide this function originally. But I found the
> > tegra_cpu_disable() was removed recently. It was replaced by the common
> > cpu_disable() function that didn't allow CPU0 to be un-plugged.
> 
> Is there a specific reason for that; is there some problem in the core
> ARM code that implies CPU0 should never be disabled?
> 
I think the CPU0 is the boot CPU for most of the case. We always need at
least one CPU online. That assumes to be the boot CPU.

> > But I had verified the CPU0 is OK to be un-plugged on the older
> > linux-next branch that tegra_cpu_disable() watn't removed yet.
> > 
> > Do you want me to add them back to support this function for Tegra114?
> 
> If there is a problem removing CPU0 in the core code, the functionality
> of this series is OK, although it's probably worth removing the parts
> that attempt to make CPU0 hot-unpluggable to reduce the diff size.
> 
> If there's no problem removing CPU0, it'd be good to make it work,
> although that could be done in followon patches.

OK. Thanks.