linux-kernel - Re: [PATCH] ARM: EXYNOS: mcpm: Don't rely on firmware's secondary_cpu_start

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Message-ID: <CADWw7OjqK3MAuqCHuv-WS3Bb2+2Q-FXth+7hqtwFoyAP6pyYhA@mail.gmail.com>
Date:	Wed, 11 Jun 2014 10:22:10 +0530
From:	Chander Kashyap <k.chander@...sung.com>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:	Doug Anderson <dianders@...omium.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	Kevin Hilman <khilman@...aro.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	Inderpal Singh <inderpal.s@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chander Kashyap <chander.kashyap@...aro.org>,
	"olof@...om.net" <olof@...om.net>,
	Tushar Behera <trblinux@...il.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Thomas Abraham <thomas.ab@...sung.com>,
	Abhilash Kesavan <a.kesavan@...sung.com>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH] ARM: EXYNOS: mcpm: Don't rely on firmware's secondary_cpu_start

Hi Doug,

On Tue, Jun 10, 2014 at 9:19 PM, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> On Tue, 10 Jun 2014, Doug Anderson wrote:
>
>> My S-state knowledge is not strong, but I believe that Lorenzo's
>> questions matter if we're using S2 for CPUidle (where we actually turn
>> off power and hot unplug CPUs) but not when we're using S1 for CPUidle
>> (where we just enter WFI/WFE).
>>

No Its not plain WFI.

All cores in Exynos5420 can be powered off independently.
This functionality has been tested.

Below is the link for the posted patches.

https://lkml.org/lkml/2014/6/10/194

And as Nicolas wrote, these patches need MCPM for that.

>> I believe that in ChromeOS we use S1 CPUidle and that it works fine.
>> We've never implemented S2 that I'm aware of.
>
> You'll have to rely on MCPM for that.  That's probably why it hasn't
> been implemented before.
>
>
> Nicolas
>
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