linux-kernel - Re: [PATCH v2 6/6] [RFC] arm: use PSCI if available

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Message-ID: <alpine.DEB.2.02.1303271109080.4430@kaball.uk.xensource.com>
Date:	Wed, 27 Mar 2013 11:15:23 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
CC:	Arnd Bergmann <arnd@...db.de>, Will Deacon <will.deacon@....com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"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>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>
Subject: Re: [PATCH v2 6/6] [RFC] arm: use PSCI if available

On Tue, 26 Mar 2013, Nicolas Pitre wrote:
> On Tue, 26 Mar 2013, Arnd Bergmann wrote:
> 
> > On Tuesday 26 March 2013, Will Deacon wrote:
> > > > They can even base the implementation of their smp_ops on the current
> > > > psci code, in order to facilitate that I could get rid of psci_ops
> > > > (which initialization is based on device tree) and export the psci_cpu_*
> > > > functions instead, so that they can be called directly by other smp_ops.
> > > 
> > > Again, I think this destroys the layering. The whole point is that the PSCI
> > > functions are called from within something that understands precisely how to
> > > talk to the firmware and what it is capable of.
> > 
> > Right, we probably the psci smp ops to be separate from the rest of the psci
> > code, but I also think that Stefano is right that we should let any platform
> > use the psci smp ops if possible, rather than having to implement their own.
> 
> Oh absolutely.  It is always best to use an existing standard.  But PSCI 
> probably won't be the only firmware interface standard.  It therefore 
> shouldn't be used as the Linux internal interface model.

I am not proposing to use PSCI as an interal Linux API.

I am proposing to use a set of PSCI based smp_ops (instead of the ones
that come with machine_desc, if any) if a PSCI node is available on
device tree.

smp_ops remains the internal Linux API.

I am also saying that we should let people reuse the PSCI functions in
their own machine-specific smp_ops, if they want to.
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