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

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Date:	Fri, 5 Apr 2013 15:36:06 -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:

> This is what happens:
> 
> - No Xen
> Xen is not running on the platform and a Xen hypervisor node is not
> available on device tree.
> Everything keeps working seamlessly, this patch doesn't change anything.
> 
> - 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.
> Because the versatile express machine sets smp_init to
> vexpress_smp_init_ops, vexpress_smp_init_ops will be called.
> vexpress_smp_init_ops sets smp_ops to vexpress_smp_ops, that *break*
> Xen.

OK I see.

> With this patch, xen_smp_init will be called instead of
> vexpress_smp_init_ops, and smp_ops will be set to psci_smp_ops,
> therefore *unbreaking* Xen.

However that breaks MCPM.

> In fact what makes this patch really necessary is smp_init together with
> the MCPM series.

Yes.

> Do you agree with me?

On the Xen issue, yes.


Nicolas
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