linux-kernel - Re: [PATCH v3] [RFC] arm: use PSCI if available

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Date:	Thu, 28 Mar 2013 12:06:52 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Will Deacon <will.deacon@....com>
cc:	Rob Herring <robherring2@...il.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"arnd@...db.de" <arnd@...db.de>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3] [RFC] arm: use PSCI if available

On Thu, 28 Mar 2013, Will Deacon wrote:

> On Thu, Mar 28, 2013 at 03:39:42PM +0000, Nicolas Pitre wrote:
> > On Thu, 28 Mar 2013, Rob Herring wrote:
> > 
> > > On 03/28/2013 09:51 AM, Nicolas Pitre wrote:
> > > > On Thu, 28 Mar 2013, Stefano Stabellini wrote:
> > > > 
> > > >> - the interface to bring up secondary cpus is different and based on
> > > >> PSCI, in fact Xen is going to add a PSCI node to the device tree so that
> > > >> Dom0 can use it.
> > > >>
> > > >> Oh wait, Dom0 is not going to use the PSCI interface even if the node is
> > > >> present on device tree because it's going to prefer the platform smp_ops
> > > >> instead.
> > > > 
> > > > Waitaminute...  I must have missed this part.
> > > > 
> > > > Who said platform specific methods must be used in preference to PSCI?
> > > 
> > > I did. Specifically, I said the platform should be allowed to provide
> > > its own smp_ops. A platform may need to do addtional things on top of
> > > PSCI for example.
> > 
> > Then the platform should have its special hook that would override the 
> > default PSCI methods.  But, by *default* the PSCI methods should be used 
> > if the related DT information is present.
> 
> I'm fine with a default PSCI-based implementation, providing that it's actually
> a layer between the smp ops and the psci code, not just glueing pointers
> together.

Absolutely.

Even in the MCPM case, the PSCI is wrapped into a MCPM backend while 
MCPM provides its own SMP ops methods.


Nicolas
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