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Re: [Xen-devel] [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.


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