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

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Message-ID: <20130327170555.GA20990@mudshark.cambridge.arm.com>
Date:	Wed, 27 Mar 2013 17:05:56 +0000
From:	Will Deacon <will.deacon@....com>
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>,
	"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 Wed, Mar 27, 2013 at 04:33:58PM +0000, Rob Herring wrote:
> On 03/27/2013 08:38 AM, Will Deacon wrote:
> > On Wed, Mar 27, 2013 at 12:50:39PM +0000, Stefano Stabellini wrote:
> >> +struct smp_operations __initdata psci_smp_ops = {
> >> +	.smp_init_cpus		= psci_smp_init_cpus,
> >> +	.smp_prepare_cpus	= psci_smp_prepare_cpus,
> >> +	.smp_secondary_init	= psci_secondary_init,
> >> +	.smp_boot_secondary	= psci_boot_secondary,
> >> +};
> >> +#endif
> > 
> > As I said before, I don't agree with bolting these two interfaces together
> > like this and, as it stands, I'm afraid I have to NAK this patch.
> > 
> > A potential alternative is to have a set of virt_smp_ops, which have
> > wrappers around the psci functions, but that requires agreement from Xen and
> > KVM to implement the same PSCI interface, which feels unfair to me.
> 
> I need the same smp ops for highbank. By using mach-virt Xen is using
> the same interface as KVM. This patch does not change that, but rather
> allows other platforms to use the same smp ops as well.
> 
> Isn't the whole point of PSCI to have a common interface? No one is
> making Xen use PSCI at all. It is a choice and since they are making
> that choice, why would the PSCI interface be different?

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.

Will
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