linux-kernel - Re: [PATCH v6 4/4] xen/arm: introduce xen_early

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Date:	Fri, 5 Apr 2013 15:41:36 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
cc:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"will.deacon@....com" <will.deacon@....com>,
	"arnd@...db.de" <arnd@...db.de>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>
Subject: Re: [PATCH v6 4/4] xen/arm: introduce xen_early_init, use PSCI on
 xen

On Fri, 5 Apr 2013, Stefano Stabellini wrote:

> On Fri, 5 Apr 2013, Stefano Stabellini wrote:
> > - we are running on Xen
> > Xen is running on the platform, we are running as a guest on Xen and an
> > hypervisor node is available on device tree.
> > Let's also assume that there aren't any "arm,cci" compatible nodes on
> > device tree because Xen wouldn't export this kind of information to any
> > guests right now. Therefore PSCI should be used to boot secondary cpus.
> 
> Just in case this isn't clear enough: we don't have big.LITTLE support 
> in Xen right now, not in the hypervisor and certainly not in guests. 
> I'm keen on having big.LITTLE support in the hypervisor (thus some 
> code similar to your MCPM patch series will probably end up in Xen at 
> some point) but I doubt we'll expose big.LITTLE to guests any time 
> soon. It's going to be years, so I am not particularly worried about 
> it right now.

I fully understand that it is unlikely that a Xen guest will "see" a 
big.LITTLE environment in the near future.

My concern is about a kernel that is _configured_ to run either on a 
native VExpress machine that might or might not be b.L, or as a Xen 
guest, in the same zImage binary.


Nicolas
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