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

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Message-Id: <201303271750.52015.arnd@arndb.de>
Date:	Wed, 27 Mar 2013 17:50:51 +0000
From:	Arnd Bergmann <arnd@...db.de>
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>,
	"nico@...aro.org" <nico@...aro.org>,
	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 Wednesday 27 March 2013, Will Deacon wrote:
> The channel is common, sure, but I wouldn't expect the semantics of each
> call to be identical between firmware implementations (going back to my
> previous examples of CPU IDs and implementation-defined state parameters).
> 
> If a platform happens to have an id-mapping from smp_operations to psci,
> then I still think there should be an indirection in there so that we have
> the flexibility to change the smp_operations if we wish and not give
> platforms the false impression that these two things are equivalent.

I think the only reasonably implementation for psci is if we can assume
that each callback with a specific property name has a well-defined behavior,
and we should mandate that every platform that implements the callbacks
we need for SMP actually implements them according to the spec.

What would be the point of a standard psci interface if the specific
implementation are not required to follow the same semantics?

	Arnd
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