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

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Message-ID: <alpine.LFD.2.03.1303281135320.1372@syhkavp.arg>
Date:	Thu, 28 Mar 2013 11:39:42 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Rob Herring <robherring2@...il.com>
cc:	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>,
	Will Deacon <will.deacon@....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, 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.

> > If DT does provide PSCI description, then PSCI should be used.  Doing 
> > otherwise is senseless.  If PSCI is not to be used, then it should not 
> > be present in DT.
> 
> You can't assume the DT and kernel are in-sync. For example, I've added
> PSCI in the firmware and DTB (part of the firmware), but the highbank
> kernel may or may not use it depending if I convert it.

If the kernel does not understand PSCI bindings in the DT, it naturally 
won't use PSCI, right?  Conversely, if the firmware and therefore 
provided DT don't have PSCI, then the PSCI enabled kernel won't use PSCI 
either. So what is the problem?


Nicolas
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